Atmospheric Chemistry and Climate Group
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   Complete list of publications


Anthropogenic short-lived halogens increase human exposure to mercury contamination due to enhanced mercury oxidation over continents

Xiao Fua, Xianyi Suna, Oleg Travnikovb, Qinyi Li, Chuang Qin, Carlos A. Cuevas, Rafael P. Fernandez, Anoop S. Mahajan, Shuxiao Wang, Tao Wang and Alfonso Saiz-Lopez

PNAS 2024 Vol. 121 No. 12 e2315058121,, 2024.


Mercury (Hg) is a contaminant of global concern, and an accurate understanding of its atmospheric fate is needed to assess its risks to humans and ecosystem health. Atmospheric oxidation of Hg is key to the deposition of this toxic metal to the Earth’s surface. Short-lived halogens (SLHs) can provide halogen radicals to directly oxidize Hg and perturb the budget of other Hg oxidants (e.g., OH and O3). In addition to known ocean emissions of halogens, recent observational evidence has revealed abundant anthropogenic emissions of SLHs over continental areas. However, the impacts of anthropogenic SLHs emissions on the atmospheric fate of Hg and human exposure to Hg contamination remain unknown. Here, we show that the inclusion of anthropogenic SLHs substantially increased local Hg oxidation and, consequently, deposition in/near Hg continental source regions by up to 20%, thereby decreasing Hg export from source regions to clean environments. Our modeling results indicated that the inclusion of anthropogenic SLHs can lead to higher Hg exposure in/near Hg source regions than estimated in previous assessments, e.g., with increases of 8.7% and 7.5% in China and India, respectively, consequently leading to higher Hg-related human health risks. These results highlight the urgent need for policymakers to reduce local Hg and SLHs emissions. We conclude that the substantial impacts of anthropogenic SLHs emissions should be included in model assessments of the Hg budget and associated health risks at local and global scales.

East Asian summer monsoon delivers large abundances of very-short-lived organic chlorine substances to the lower stratosphere

Laura L. Pan, Elliot L. Atlas, Shawn B. Honomichl, Warren P. Smith, Douglas E. Kinnison, Susan Solomon, Michelle L. Santee, Alfonso Saiz-Lopez, Johannes C. Laube, Bin Wang, Rei Ueyama, James F. Bresch, Rebecca S. Hornbrook, Eric C. Apel, Alan J. Hills, Victoria Treadaway, Katie Smith, Sue Schauffler, Stephen Donnelly, Roger Hendershot, Richard Lueb, Teresa Campos, Silvia Viciani, Francesco D’Amato, Giovanni Bianchini, Marco Barucci, James R. Podolske, Laura T. Iraci, Colin Gurganus, Paul Bui, Jonathan M. Dean-Day, Luis Millán, Ju-Mee Ryoo, Barbara Barletta, Ja-Ho Koo, Joowan Kim, Qing Liang, William J. Randel, Troy Thornberry and Paul A. Newman.

PNAS Vol. 121, No. 12, e2318716121,, 2024.


Deep convection in the Asian summer monsoon is a significant transport process for lifting pollutants from the planetary boundary layer to the tropopause level. This process enables efficient injection into the stratosphere of reactive species such as chlorinated very-short-lived substances (Cl-VSLSs) that deplete ozone. Past studies of convective transport associated with the Asian summer monsoon have focused mostly on the south Asian summer monsoon. Airborne observations reported in this work identify the East Asian summer monsoon convection as an effective transport pathway that carried record-breaking levels of ozone-depleting Cl-VSLSs (mean organic chlorine from these VSLSs ~500 ppt) to the base of the stratosphere. These unique observations show total organic chlorine from VSLSs in the lower stratosphere over the Asian monsoon tropopause to be more than twice that previously reported over the tropical tropopause. Considering the recently observed increase in Cl-VSLS emissions and the ongoing strengthening of the East Asian summer monsoon under global warming, our results highlight that a reevaluation of the contribution of Cl-VSLS injection via the Asian monsoon to the total stratospheric chlorine budget is warranted.

Evaluating the Model Representation of Asian Summer Monsoon Upper Troposphere and Lower Stratosphere Transport and Composition Using Airborne In Situ Observations

Warren P. Smith, Laura L. Pan, Douglas Kinnison, Elliot Atlas, Shawn Honomichl, Jun Zhang, Simone Tilmes, Rafael P. Fernandez, Alfonso Saiz‐Lopez, Victoria Treadaway, Karina E. Adcock, Johannes C. Laube, Marc von Hobe, Corinna Kloss, Silvia Viciani, Francesco D’Amato, C. Michael Volk and Fabrizio Ravegnani.

Geophysical Research: Atmospheres, 129, e2023JD039756., 2024.


Chemistry Climate Models (CCMs) are essential tools for characterizing and predicting the role of atmospheric composition and chemistry in Earth's climate system. This study demonstrates the use of airborne in situ observations to diagnose the representation of chemical composition and transport by CCMs. Process-based diagnostics using dynamical and chemical coordinates are presented which minimize the spatial and temporal sampling differences between airborne in situ measurements and CCM grid points. The chosen process is the chemical impact of the Asian summer monsoon (ASM), where deep convection serves as a rapid transport pathway for surface emissions to reach the upper troposphere and lower stratosphere (UTLS). We examine two CCM configurations for their representation of the ASM UTLS using a set of airborne observations from south Asia. The diagnostics reveal good model performance at representing tropospheric tracer distribution throughout the troposphere and lower stratosphere, and excellent representation of chemical aging in the lower stratosphere when chemical loss is dominated by photolysis. Identified model limitations include the use of zonally averaged mole fraction boundary conditions for species with sufficiently short tropospheric lifetimes, which may obscure enhanced regional emissions sources. Overall, the diagnostics underscore the skill of current-generation models at representing pollution transport from the boundary layer to the stratosphere via the ASM mechanism, and demonstrate the strength of airborne in situ observations toward characterizing this representation.

Evaluating the potential of iron-based interventions in methane reduction and climate mitigation

Daphne Meidan, Qinyi Li, Carlos A Cuevas, Scott C Doney, Rafael P Fernandez, Maarten M J W van Herpen, Matthew S Johnson, Douglas E Kinnison, Longlei Li, Douglas S Hamilton, Alfonso Saiz-Lopez, Peter Hess and Natalie M Mahowald

Environmental Research Letters, Volume 19, Number 5, DOI 10.1088/1748-9326/ad3d72, 2024


Keeping global surface temperatures below international climate targets will require substantial measures to control atmospheric CO2 and CH4 concentrations. Recent studies have focused on interventions to decrease CH4 through enhanced atmospheric oxidation. Here for the first time using a set of models, we evaluate the effect of adding iron aerosols to the atmosphere to enhance molecular chlorine production, and thus enhance the atmospheric oxidation of methane and reduce its concentration. Using different iron emission sensitivity scenarios, we examine the potential role and impact of enhanced iron emissions on direct interactions with solar radiation, and on the chemical and radiative response of methane. Our results show that the impact of iron emissions on CH4 depends sensitively on the location of the iron emissions. In all emission regions there is a threshold in the amount of iron that must be added to remove methane. Below this threshold CH4 increases. Even once that threshold is reached, the iron-aerosol driven chlorine-enhanced impacts on climate are complex. The radiative forcing of both methane and ozone are decreased in the most efficient regions but the direct effect due to the addition of absorbing iron aerosols tends to warm the planet. Adding any anthropogenic aerosol may also cool the planet due to aerosol cloud interactions, although these are very uncertain, and here we focus on the unique properties of adding iron aerosols. If the added emissions have a similar distribution as current shipping emissions, our study shows that the amount of iron aerosols that must be added before methane decreases is 2.5 times the current shipping emissions of iron aerosols, or 6 Tg Fe yr−1 in the most ideal case examined here. Our study suggests that the photoactive fraction of iron aerosols is a key variable controlling the impact of iron additions and poorly understood. More studies of the sensitivity of when, where and how iron aerosols are added should be conducted. Before seriously considering this method, additional impacts on the atmospheric chemistry, climate, environmental impacts and air pollution should be carefully assessed in future studies since they are likely to be important.

Global retrieval of stratospheric and tropospheric BrO columns from the Ozone Mapping and Profiler Suite Nadir Mapper (OMPS-NM) on board the Suomi-NPP satellite

Heesung Chong, Gonzalo González Abad, Caroline R. Nowlan, Christopher Chan Miller, Alfonso Saiz-Lopez, Rafael P. Fernandez, Hyeong-Ahn Kwon, Zolal Ayazpour, Huiqun Wang, Amir H. Souri, Xiong Liu, Kelly Chance, Ewan O'Sullivan, Jhoon Kim, Ja-Ho Koo, William R. Simpson, François Hendrick, Richard Querel, Glen Jaross, Colin Seftor, and Raid M. Suleiman.

Atmospheric Measurement Techniques, Volume 17, issue 9, 17, 2873–2916,, 2024.


Quantifying the global bromine monoxide (BrO) budget is essential to understand ozone chemistry better. In particular, the tropospheric BrO budget has not been well characterized. Here, we retrieve nearly a decade (February 2012–July 2021) of stratospheric and tropospheric BrO vertical columns from the Ozone Mapping and Profiling Suite Nadir Mapper (OMPS-NM) on board the Suomi National Polar-orbiting Partnership (Suomi-NPP) satellite. In quantifying tropospheric BrO enhancements from total slant columns, the key aspects involve segregating them from stratospheric enhancements and applying appropriate air mass factors. To address this concern and improve upon the existing methods, our study proposes an approach that applies distinct BrO vertical profiles based on the presence or absence of tropospheric BrO enhancement at each pixel, identifying it dynamically using a satellite-derived stratospheric-ozone–BrO relationship. We demonstrate good agreement for both stratosphere (r = 0.81–0.83) and troposphere (r = 0.50–0.70) by comparing monthly mean BrO vertical columns from OMPS-NM with ground-based observations from three stations (Lauder, Utqiaġvik, and Harestua). Although algorithm performance is primarily assessed at high latitudes, the OMPS-NM BrO retrievals successfully capture tropospheric enhancements not only in polar regions but also in extrapolar areas, such as the Rann of Kutch and the Great Salt Lake. We also estimate random uncertainties in the retrievals pixel by pixel, which can assist in quantitative applications of the OMPS-NM BrO dataset. Our BrO retrieval algorithm is designed for cross-sensor applications and can be adapted to other space-borne ultraviolet spectrometers, contributing to the creation of continuous long-term satellite BrO observation records.

Improving Simulation of Gas-Particle Partitioning of Atmospheric Mercury Using CMAQ-newHg-Br v2

L. Wu, H. Mao, Z. Ye, T. S. Dibble, A. Saiz-Lopez, Y. Zhang

Journal of Advances in Modeling Earth Systems, 16, e2023MS003823,, 2024.


Mercury (Hg) is a global pollutant whose atmospheric deposition is a major input to the terrestrial and oceanic ecosystems. Gas-particle partitioning (GPP) of gaseous oxidized mercury (GOM) redistributes speciated Hg between gas and particulate phase and can subsequently alter Hg deposition flux. Most 3-dimensional chemical transport models either neglected the Hg GPP process or parameterized it with measurement data limited in time and space. In this study, CMAQ-newHg-Br (Ye et al., 2018, was updated to CMAQ-newHg-Br v2 by implementing a new GPP scheme and the most up-to-date Hg redox chemistry and was run for the northeastern United States over January-November 2010. CMAQ-newHg-Br v2 reproduced the measured spatiotemporal distributions of gaseous elemental mercury (GEM) and particulate bound mercury (PBM) concentrations and Hg wet deposition flux within reasonable ranges and simulated dry deposition flux in agreement with previous studies. The GPP scheme improved the simulation of PBM via increasing winter-, spring- and fall-time PBM concentrations by threefold. It also improved simulated Hg wet deposition flux with an increase of 2.1 ± 0.7 μgm2 in the 11-month accumulated amount, offsetting half of the decreasing effect of the updated chemistry (−4.2 ± 1.8 μgm2). Further, the GPP scheme captured the observed Kp-T relationship as reported in previous studies without using measurement data and showed advantages at night and in rural/remote areas where existing empirical parameterizations failed. Our study demonstrated CMAQ-newHg-Br v2 a promising assessment tool to quantify impacts of climate change and emission reduction policy on Hg cycling.

Investigating halogens and MSA in the Southern Hemisphere: A spatial analysis

Delia Segato, Elizabeth R. Thomas, Dieter Tetzner, Sarah Jackson, Dorothea Elisabeth Moser, Clara Turetta, Rafael P. Fernandez, Alfonso Saiz-Lopez, Joel Pedro, Bradley Markle and Andrea Spolaor

Atmospheric Environment 319 (2024) 120279,


Sub-Antarctic islands and Antarctic coastal regions provide valuable sites for investigating environmental processes in the Southern Ocean. The fact that these sites are situated within the sea ice zone underscores their significance in investigating the impact of sea ice on the chemical composition of the boundary layer. In this study we report multi-year average levels of marine aerosols, including bromine, sodium, methanesulphonic acid and iodine, measured in five firn cores collected from sub-Antarctic Islands and coastal Antarctic sites. The records are compared with published Antarctic records to explore the spatial distribution of these species in the Antarctic region and their relationship with sea ice variability. Being mainly sourced from sea-salt aerosols, sodium and bromine exhibit the largest concentrations in the sub-Antarctic region, with progressively reduced deposition from the coast towards the central Antarctic plateau. Due to its gas-phase chemistry, bromine is depleted with respect to sodium in the sub-Antarctic sites. Bromine emitted in the form of sea-salt aerosols undergoes multi-phase recycling in the lower troposphere and, together with gas-phase bromine emitted from sea ice, is likely to be transported away from the source, depositing in enriched concentrations in the plateau compared to the Br/Na sea-water mass ratio. Similarly to bromine and sodium, methanesulphonic acid and iodine are found in higher concentrations in the sub-Antarctic sites, especially where the ocean is sea ice-covered during spring as primary production is stronger than in the ice-free ocean. Sea-salt mediated recycling of gas-phase iodine enhances its atmospheric lifetime, delivering enriched iodine depositions to the Antarctic plateau. Depicting the spatial distribution of these elements is of great importance for understanding the processes delivering these impurities around Antarctica.


Measurements and Modeling of the Interhemispheric Differences of Atmospheric Chlorinated Very Short-Lived Substances

Behrooz Roozitalab, Louisa K. Emmons, Rebecca S. Hornbrook, Douglas E. Kinnison, Rafael P. Fernandez, Qinyi Li, Alfonso Saiz-Lopez, Ryan Hossaini, Carlos A. Cuevas, Alan J. Hills, Stephen A. Montzka, Donald R. Blake, William H. Brune, Patrick R. Veres and Eric C. Apel

Journal of Geophysical Research: Atmospheres, 129, e2023JD039518.


Chlorinated very short-lived substances (Cl-VSLS) are ubiquitous in the troposphere and can contribute to the stratospheric chlorine budget. In this study, we present measurements of atmospheric dichloromethane (CH2Cl2), tetrachloroethene (C2Cl4), chloroform (CHCl3), and 1,2-dichloroethane (1,2-DCA) obtained during the National Aeronautics and Space Administration (NASA) Atmospheric Tomography (ATom) global-scale aircraft mission (2016–2018), and use the Community Earth System Model (CESM) updated with recent chlorine chemistry to further investigate their global tropospheric distribution. The measured global average Cl-VSLS mixing ratios, from 0.2 to 13 km altitude, were 46.6 ppt (CH2Cl2), 9.6 ppt (CHCl3), 7.8 ppt (1,2-DCA), and 0.84 ppt (C2Cl4) measured by the NSF NCAR Trace Organic Analyzer (TOGA) during ATom. Both measurements and model show distinct hemispheric gradients with the mean measured Northern to Southern Hemisphere (NH/SH) ratio of 2 or greater for all four Cl-VSLS. In addition, the TOGA profiles over the NH mid-latitudes showed general enhancements in the Pacific basin compared to the Atlantic basin, with up to ∼18 ppt difference for CH2Cl2 in the mid troposphere. We tagged regional source emissions of CH2Cl2 and C2Cl4 in the model and found that Asian emissions dominate the global distributions of these species both at the surface (950 hPa) and at high altitudes (150 hPa). Overall, our results confirm relatively high mixing ratios of Cl-VSLS in the UTLS region and show that the CESM model does a reasonable job of simulating their global abundance but we also note the uncertainties with Cl-VSLS emissions and active chlorine sources in the model. These findings will be used to validate future emission inventories and to investigate the fast convective transport of Cl-VSLS to the UTLS region and their impact on stratospheric ozone.

Opinion: A research roadmap for exploring atmospheric methane removal via iron salt aerosol

Katrine A. Gorham, Sam Abernethy, Tyler R. Jones, Peter Hess, Natalie M. Mahowald, Daphne Meidan, Matthew S. Johnson, Maarten M. J. W. van Herpen, Yangyang Xu, Alfonso Saiz-Lopez, Thomas Röckmann, Chloe A. Brashear, Erika Reinhardt, and David Mann.

Atmospheric Chemistry and Physics, Volume 24, issue 9, 5659–5670,, 2024.


The escalating climate crisis requires rapid action to reduce the concentrations of atmospheric greenhouse gases and lower global surface temperatures. Methane will play a critical role in near-term warming due to its high radiative forcing and short atmospheric lifetime. Methane emissions have accelerated in recent years, and there is significant risk and uncertainty associated with the future growth in natural emissions. The largest natural sink of methane occurs through oxidation reactions with atmospheric hydroxyl and chlorine radicals. Enhanced atmospheric oxidation could be a potential approach to remove atmospheric methane. One method proposes the addition of iron salt aerosol (ISA) to the atmosphere, mimicking a natural process proposed to occur when mineral dust mixes with chloride from sea spray to form iron chlorides, which are photolyzed by sunlight to produce chlorine radicals. Under the right conditions, lofting ISA into the atmosphere could potentially reduce atmospheric methane concentrations and lower global surface temperatures. Recognizing that potential atmospheric methane removal must only be considered an additive measure – in addition to, not replacing, crucial anthropogenic greenhouse gas emission reductions and carbon dioxide removal – roadmaps can be a valuable tool to organize and streamline interdisciplinary and multifaceted research to efficiently move towards understanding whether an approach may be viable and socially acceptable or if it is nonviable and further research should be deprioritized. Here we present a 5-year research roadmap to explore whether ISA enhancement of the chlorine radical sink could be a viable and socially acceptable atmospheric methane removal approach.

Photodissociation of the CH2Br radical: A theoretical study

F. Charfeddine, A. Zanchet, O. Yazidi, C. A. Cuevas, A. Saiz-Lopez, L. Bañares and A. García-Vela

The Journal of Chemical Physics 160, 074301,


Bromine atom (Br) reactions lead to ozone depletion in the troposphere and stratosphere. Photodegradation of bromocarbons is one of the main sources of bromine atoms in the atmosphere. Here, we use high-level ab initio methods, including spin–orbit effects, to study the photodissociation of the CH2Br radical. All possible fragmentation pathways, namely CH2Br + hν → CH2 + Br, HCBr + H, and CBr + H2, have been analyzed. Potential-energy curves of the ground and several excited electronic states along the corresponding dissociating bond distance of each pathway have been calculated. Considering the actinic fluxes of solar irradiation in the troposphere and in the stratosphere in the relevant range of frequencies, it is found that the first five excited states of CH2Br can be accessed from the ground state. Analysis of the potential curves shows that the pathways producing CH2 + Br and HCBr + H can proceed through a fast direct dissociation mechanism, while the pathway leading to CBr + H2 involves much slower dissociation mechanisms like internal conversion between electronic states, predissociation, or tunneling through exit barriers. The main implications are that the two faster channels are predicted to be dominant, and the slower pathway is expected to be less relevant. The tropospheric and stratospheric solar actinic fluxes also allow for further dissociation of the HCBr and CBr fragments, generating additional Br atoms, provided that they survive possible collisions with other atmospheric reagents. Finally, we discuss the possible effect of each of the three CH2Br dissociation pathways on the depletion of atmospheric ozone.

Typhoon- and pollution-driven enhancement of reactive bromine in the mid-latitude marine boundary layer

Shanshan Wang, Qinyi Li, Ruifeng Zhang, Anoop Sharad Mahajan, Swaleha Inamdar, Nuria Benavent, Sanbao Zhang, Ruibin Xue, Jian Zhu, Chenji Jin, Yan Zhang, Xiao Fu, Alba Badia, Rafael P. Fernandez, Carlos A. Cuevas, Tao Wang, Bin Zhou and Alfonso Saiz-Lopez

National Science Review, 11: 14 nwae074,, 2024


Tropospheric reactive bromine is important for atmospheric chemistry, regional air pollution, and global climate. Previous studies have reported measurements of atmospheric reactive bromine species in different environments, and proposed their main sources, e.g. sea-salt aerosol (SSA), oceanic biogenic activity, polar snow/ice, and volcanoes. Typhoons and other strong cyclonic activities (e.g. hurricanes) induce abrupt changes in different earth system processes, causing widespread destructive effects. However, the role of typhoons in regulating reactive bromine abundance and sources remains unexplored. Here, we report field observations of bromine oxide (BrO), a critical indicator of reactive bromine, on the Huaniao Island (HNI) in the East China Sea in July 2018. We observed high levels of BrO below 500 m with a daytime average of 9.7 ± 4.2 pptv and a peak value of ∼26 pptv under the influence of a typhoon. Our field measurements, supported by model simulations, suggest that the typhoon-induced drastic increase in wind speed amplifies the emission of SSA, significantly enhancing the activation of reactive bromine from SSA debromination. We also detected enhanced BrO mixing ratios under high NOx conditions (ppbv level) suggesting a potential pollution-induced mechanism of bromine release from SSA. Such elevated levels of atmospheric bromine noticeably increase ozone destruction by as much as ∼40% across the East China Sea. Considering the high frequency of cyclonic activity in the northern hemisphere, reactive bromine chemistry is expected to play a more important role than previously thought in affecting coastal air quality and atmospheric oxidation capacity. We suggest that models need to consider the hitherto overlooked typhoon- and pollution-mediated increase in reactive bromine levels when assessing the synergic effects of cyclonic activities on the earth system.

200-year ice core bromine reconstruction at Dome C (Antarctica): observational and modelling results

François Burgay, Rafael Pedro Fernández, Delia Segato, Clara Turetta, Christopher S. Blaszczak-Boxe, Rachael H. Rhodes, Claudio Scarchilli, Virginia Ciardini, Carlo Barbante, Alfonso Saiz-Lopez and Andrea Spolaor.

The Cryosphere, 17, 391–405, 2023


Bromine enrichment (Brenr) has been proposed as an ice core proxy for past sea-ice reconstruction. Understanding the processes that influence bromine preservation in the ice is crucial to achieve a reliable interpretation of ice core signals and to potentially relate them to past sea-ice variability. Here, we present a 210-years bromine record that sheds light on the main processes controlling bromine preservation in the snow and ice at Dome C, East Antarctic plateau. Using observations alongside a modelling approach, we demonstrate that the bromine signal is preserved at Dome C, and it is not affected by the strong variations in ultraviolet radiation reaching the Antarctic plateau due to the stratospheric ozone hole. Based on this, we investigate whether the Dome C Brenr record can be used as an effective tracer of past Antarctic sea-ice. Due to the limited time window covered by satellite measurements and the low sea-ice variability observed during the last 30 years in East Antarctica, at this stage we cannot fully validate Brenr as an effective proxy for past sea-ice reconstructions at Dome C.

Arctic mercury flux increased through the Last Glacial Termination with a warming climate

Delia Segato, Alfonso Saiz-Lopez, Anoop Sharad Mahajan, Feiyue Wang, Juan Pablo Corella, Carlos Alberto Cuevas, Tobias Erhardt, Camilla Marie Jensen, Chantal Zeppenfeld, Helle Astrid Kjær, Clara Turetta, Warren Raymond Lee Cairns, Carlo Barbante and Andrea Spolaor.

Nature Geoscience volume 16, pages 439–445,


Mercury is a pollutant of global concern, especially in the Arctic, where high levels are found in biota despite its remote location. Mercury is transported to the Arctic via atmospheric, oceanic and riverine long-range pathways, where it accumulates in aquatic and terrestrial ecosystems. While present-day mercury deposition in the Arctic from natural and anthropogenic emissions is extensively studied, the control of past climate changes on natural mercury variability remains unknown. Here we present an Arctic mercury record covering the Last Glacial Termination to the early Holocene epoch (15.7–9.0 thousand years before 2000 ce), collected as part of the East Greenland Ice-Core Project. We find a threefold increase in mercury depositional fluxes from the Last Glacial Termination into the early Holocene, which coincided with abrupt regional climate warming. Atmospheric chemistry modelling, combined with available sea-ice proxies, indicates that oceanic mercury evaporation and atmospheric bromine drove the increase in mercury flux during this climatic transition. Our results suggest that environmental changes associated with climate warming may contribute to increasing mercury levels in Arctic ecosystems.

Bromine, iodine and sodium along the EAIIST traverse: Bulk and surface snow latitudinal variability

G. Celli, W.R.L. Cairns, C. Scarchilli, C.A. Cuevas, A. Saiz-Lopez, J. Savarino, B. Stenni, M. Frezzotti, S. Becagli, B. Delmonte, H. Angot, R.P. Fernandez, A. Spolaor.

Environmental Research, Volume 239, Part 1, 117344,, 2023.


During the East Antarctic International Ice Sheet Traverse (Eaiist, december 2019), in an unexplored part of the East Antarctic Plateau, snow samples were collected to expand our knowledge of the latitudinal variability of iodine, bromine and sodium as well as their relation in connection with emission processes and photochemical activation in this unexplored area. A total of 32 surface (0–5 cm) and 32 bulk (average of 1 m depth) samples were taken and analysed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Our results show that there is no relevant latitudinal trend for bromine and sodium. For bromine they also show that it has no significant post-depositional mechanisms while its inland surface snow concentration is influenced by spring coastal bromine explosions. Iodine concentrations are several orders of magnitude lower than bromine and sodium and they show a decreasing trend in the surface samples concentration moving southward. This suggests that other processes affect its accumulation in surface snow, probably related to the radial reduction in the ozone layer moving towards central Antarctica. Even though all iodine, bromine and sodium present similar long-range transport from the dominant coastal Antarctic sources, the annual seasonal cycle of the ozone hole over Antarctica increases the amount of UV radiation (in the 280–320 nm range) reaching the surface, thereby affecting the surface snow photoactivation of iodine. A comparison between the bulk and surface samples supports the conclusion that iodine undergoes spring and summer snow recycling that increases its atmospheric lifetime, while it tends to accumulate during the winter months when photochemistry ceases.

Comparing the Effect of Anthropogenically Amplified Halogen Natural Emissions on Tropospheric Ozone Chemistry Between Pre-Industrial and Present-Day

Javier A. Barrera, Douglas E. Kinnison, Rafael P. Fernandez, Jean-François Lamarque, Carlos A. Cuevas, Simone Tilmes and Alfonso Saiz-Lopez.

Geophysical Research: Atmospheres, 128, e2022JD038283,


Reactive halogens (X + XO, X = I, Br or Cl) catalytically destroy a fraction of tropospheric ozone under present-day (PD) conditions, however, their distribution and potential impact on tropospheric ozone under pre-industrial (PI) conditions remain largely unexplored. This study uses the Community Atmosphere Model with Chemistry (CAM-Chem) to investigate the effect of anthropogenically amplified natural emissions of halogenated species and their subsequent chemistry on tropospheric ozone under PI and PD atmospheric conditions. Model results show that the global tropospheric ozone depletion due to natural halogens is slightly more sensitive in PI than PD, with percentage changes in tropospheric ozone burden (TOB) of −14.1 ± 0.6% for PI and −12.9 ± 0.6% for PD. Individually, the role of iodine and chlorine in ozone depletion is equivalent in both periods (ΔTOB I: ∼−7% and ΔTOB Cl: ∼−2.5%), while bromine plays a larger role in PI (ΔTOB Br:−5.5 ± 0.6%) versus PD (ΔTOB Br: −4.3 ± 0.7%). The increase in anthropogenic ozone precursor emissions
from PI to PD has amplified the natural emission of inorganic halogens and led to a shift in the partitioning of inorganic halogens from reactive to reservoir species. Consequently, halogen-driven ozone depletion from the surface to the free troposphere is larger in PI than PD. In contrast, in the upper troposphere, the ozone depletion is larger in PD influenced mainly by stratospheric intrusion of reactive halogens from long-lived species. This study highlights the importance of including a complete chemical coupling of natural halogens and atmospheric pollutants in chemistry-climate models to adequately assess their effects on tropospheric ozone in a changing climate.

Differences in iodine chemistry over the Antarctic continent

Anoop S. Mahajan, Shrutika Wagh, Rafael P. Fernández, Surendra Singh, Silvia Bucci and Alfonso Saiz-López

Polar Science,, 2023.


High concentrations of iodine oxide (IO) have been reported over west Antarctica, with areas around the Weddell Sea showing a peak in spring. However, stations in east Antarctica show much lower values during summer, although observations over spring are still missing. Here, we present the first year-long observations of IO outside the Weddell Sea region using a multi-axis differential optical absorption spectrometer (MAX-DOAS) over the Bharati station (69.41°S, 76.19°E). Observations show that iodine chemistry is less active than over the Weddell Sea, even during springtime, with IO mixing ratios below 2 pptv throughout the sunlit period. A slight increase in IO is observed in spring, although it is a factor of 10 lower than the Weddell Sea region. We identify the variations in drivers in the different regions using sea ice concentrations, sea ice thickness and chlorophyll concentrations. We use a global model which uses a parameterization for iodine emissions based on a combination of these factors. The model reproduces the high concentrations over the Weddell Sea and the low concentrations over Bharati throughout the year, shedding light on the environmental factors, sources and chemistry of iodine in Antarctica. Even at small concentrations, iodine can enhance ozone loss caused by bromine chemistry over east Antarctica, although this impact is lower than in the west Antarctic.

Evidence of nitrate-based nighttime atmospheric nucleation driven by marine microorganisms in the South Pacific

Guillaume Chamba, Matti Rissanen, Theresa Barthelmeß, Alfonso Saiz-Lopez, Clémence Rose, Siddharth Iyer, Alexia Saint-Macary, Manon Rocco, Karl Safi, Stacy Deppeler, Neill Barr, Mike Harvey, Anja Engel, Erin Dunne, Cliff S. Law and Karine Sellegri.

PNAS, Vol. 120, No. 48, e2308696120,, 2023.


Our understanding of ocean–cloud interactions and their effect on climate lacks insight into a key pathway: do biogenic marine emissions form new particles in the open ocean atmosphere? Using measurements collected in ship-borne air–sea interface tanks deployed in the Southwestern Pacific Ocean, we identified new particle formation (NPF) during nighttime that was related to plankton community composition. We show that nitrate ions are the only species for which abundance could support NPF rates in our semicontrolled experiments. Nitrate ions also prevailed in the natural pristine marine atmosphere and were elevated under higher sub-10 nm particle concentrations. We hypothesize that these nucleation events were fueled by complex, short-term biogeochemical cycling involving the microbial loop. These findings suggest a new perspective with a previously unidentified role of nitrate of marine biogeochemical origin in aerosol nucleation.

Global environmental implications of atmospheric methane removal through chlorine-mediated chemistry-climate interactions

Qinyi Li, Daphne Meidan, Peter Hess, Juan A. Añel, Carlos A. Cuevas, Scott Doney, Rafael P. Fernandez, Maarten van Herpen, Lena Höglund-Isaksson, Matthew S. Johnson, Douglas E. Kinnison, Jean-François Lamarque, Thomas Röckmann, Natalie M. Mahowald and Alfonso Saiz-Lopez.

Nature Communications, volume 14, Article number: 4045,


Atmospheric methane is both a potent greenhouse gas and photochemically active, with approximately equal anthropogenic and natural sources. The addition of chlorine to the atmosphere has been proposed to mitigate global warming through methane reduction by increasing its chemical loss. However, the potential environmental impacts of such climate mitigation remain unexplored. Here, sensitivity studies are conducted to evaluate the possible effects of increasing reactive chlorine emissions on the methane budget, atmospheric composition and radiative forcing. Because of non-linear chemistry, in order to achieve a reduction in methane burden (instead of an increase), the chlorine atom burden needs to be a minimum of three times the estimated present-day burden. If the methane removal target is set to 20%, 45%, or 70% less global methane by 2050 compared to the levels in the Representative Concentration Pathway 8.5 scenario (RCP8.5), our modeling results suggest that additional chlorine fluxes of 630, 1250, and 1880 Tg Cl/year, respectively, are needed. The results show that increasing chlorine emissions also induces significant changes in other important climate forcers. Remarkably, the tropospheric ozone decrease is large enough that the magnitude of radiative forcing decrease is similar to that of methane. Adding 630, 1250, and 1880 Tg Cl/year to the RCP8.5 scenario, chosen to have the most consistent current-day trends of methane, will decrease the surface temperature by 0.2, 0.4, and 0.6 °C by 2050, respectively. The quantity and method in which the chlorine is added, its interactions with climate pathways, and the potential environmental impacts on air quality and ocean acidity, must be carefully considered before any action is taken.

Impacts of ocean biogeochemistry on atmospheric chemistry. Impacts of ocean biogeochemistry on atmospheric chemistry

Liselotte Tinel, Jonathan Abbatt, Eric Saltzman, Anja Engel, Rafael Fernandez, Qinyi Li, Anoop S. Mahajan, Melinda Nicewonger, Gordon Novak, Alfonso Saiz-Lopez, Stephanie Schneider and Shanshan Wang.

Elementa: Science of the Anthropocene (2023) 11 (1): 00032,, 2023.


Ocean biogeochemistry involves the production and consumption of an array of organic compounds and halogenated trace gases that influence the composition and reactivity of the atmosphere, air quality, and the climate system. Some of these molecules affect tropospheric ozone and secondary aerosol formation and impact the atmospheric oxidation capacity on both regional and global scales. Other emissions undergo transport to the stratosphere, where they contribute to the halogen burden and influence ozone. The oceans also comprise a major sink for highly soluble or reactive atmospheric gases. These issues are an active area of research by the SOLAS (Surface Ocean Lower Atmosphere) community. This article provides a status report on progress over the past decade, unresolved issues, and future research directions to understand the influence of ocean biogeochemistry on gas-phase atmospheric chemistry. Common challenges across the subject area involve establishing the role that biology plays in controlling the emissions of gases to the atmosphere and the inclusion of such complex processes, for example involving the sea surface microlayer, in large-scale global models.

Increasing contribution of nighttime nitrogen chemistry to wintertime haze formation in Beijing observed during COVID-19 lockdowns

Chao Yan, Yee Jun Tham, Wei Nie, Men Xia, Haichao Wang, Yishuo Guo, Wei Ma, Junlei Zhan, Chenjie Hua, Yuanyuan Li, Chenjuan Deng, Yiran Li, Feixue Zheng, Xin Chen, Qinyi Li, Gen Zhang, Anoop S. Mahajan, Carlos A. Cuevas, Dan Dan Huang, Zhe Wang, Yele Sun, Alfonso Saiz-Lopez, Federico Bianchi, Veli-Matti Kerminen, Douglas R. Worsnop, Neil M. Donahue, Jingkun Jiang, Yongchun Liu, Aijun Ding and Markku Kulmala.

Nature Geoscience,, 2023.


Nitrate comprises the largest fraction of fine particulate matter in China during severe haze. Consequently, strict control of nitrogen oxides (NOx) emissions has been regarded as an effective measure to combat air pollution. However, this notion is challenged by the persistent severe haze pollution observed during the COVID-19 lockdown when NOx levels substantially declined. Here we present direct field evidence that diminished nitrogen monoxide (NO) during the lockdown activated nocturnal nitrogen chemistry, driving severe haze formation. First, dinitrogen pentoxide (N2O5) heterogeneous reactions dominate particulate nitrate (pNO3−) formation during severe pollution, explaining the higher-than-normal pNO3− fraction in fine particulate matter despite the substantial NOx reduction. Second, N2O5 heterogeneous reactions provide a large source of chlorine radicals on the following day, contributing drastically to the oxidation of volatile organic compounds, and thus the formation of oxygenated organic molecules and secondary organic aerosol. Our findings highlight the increasing importance of such nocturnal nitrogen chemistry in haze formation caused by NOx reduction, motivating refinements to future air pollution control strategies.

Marine biogenic emissions of benzene and toluene and their contribution to secondary organic aerosols over the polar oceans

Charel Wohl, Qinyi Li, Carlos A. Cuevas, Rafael P. Fernandez, Mingxi Yang, Alfonso Saiz-Lopez, Rafel Simó.

Science Advances, Vol 9, Issue 4, DOI: 10.1126/sciadv.add9031, 2023.


Reactive trace gas emissions from the polar oceans are poorly characterized, even though their effects on atmospheric chemistry and aerosol formation are crucial for assessing current and preindustrial aerosol forcing on climate. Here, we present seawater and atmospheric measurements of benzene and toluene, two gases typically associated with pollution, in the remote Southern Ocean and the Arctic marginal ice zone. Their distribution suggests a marine biogenic source. Calculated emission fluxes were 0.023 ± 0.030 (benzene) and 0.039 ± 0.036 (toluene) and 0.023 ± 0.028 (benzene) and 0.034 ± 0.041 (toluene) μmol m−2 day−1 for the Southern Ocean and the Arctic, respectively. Including these average emissions in a chemistry-climate model increased secondary organic aerosol mass concentrations only by 0.1% over the Arctic but by 7.7% over the Southern Ocean, with transient episodes of up to 77.3%. Climate models should consider the hitherto overlooked emissions of benzene and toluene from the polar oceans.

Modelling the coupled mercury-halogen-ozone cycle in the central Arctic during spring

Shaddy Ahmed, Jennie L. Thomas, Hélène Angot, Aurélien Dommergue, Stephen D. Archer, Ludovic Bariteau, Ivo Beck, Nuria Benavent, Anne-Marlene Blechschmidt, Byron Blomquist, Matthew Boyer, Jesper H. Christensen, Sandro Dahlke, Ashu Dastoor, Detlev Helmig, Dean Howard, Hans-Werner Jacobi, Tuija Jokinen, Rémy Lapere, Tiia Laurila, Lauriane L. J. Quéléver, Andreas Richter, Andrei Ryjkov, Anoop S. Mahajan, Louis Marelle, Katrine Aspmo Pfaffhuber, Kevin Posman, Annette Rinke, Alfonso Saiz-Lopez, Julia Schmale, Henrik Skov, Alexandra Steffen, Geoff Stupple, Jochen Stutz, Oleg Travnikov and Bianca Zilker.

Elementa Science of the Anthropocene 11: 1, DOI:


Near-surface mercury and ozone depletion events occur in the lowest part of the atmosphere during Arctic spring. Mercury depletion is the first step in a process that transforms long-lived elemental mercury to more reactive forms within the Arctic that are deposited to the cryosphere, ocean, and other surfaces, which can ultimately get integrated into the Arctic food web. Depletion of both mercury and ozone occur due to the presence of reactive halogen radicals that are released from snow, ice, and aerosols. In this work, we added a detailed description of the Arctic atmospheric mercury cycle to our recently published version of the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem 4.3.3) that includes Arctic bromine and chlorine chemistry and activation/recycling on snow and aerosols. The major advantage of our modelling approach is the online calculation of bromine concentrations and emission/recycling that is required to simulate the hourly and daily variability of Arctic mercury depletion. We used this model to study coupling between reactive cycling of mercury, ozone, and bromine during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) spring season in 2020 and evaluated results compared to land-based, ship-based, and remote sensing observations. The model predicts that elemental mercury oxidation is driven largely by bromine chemistry and that particulate mercury is the major form of oxidized mercury. The model predicts that the majority (74%) of oxidized mercury deposited to land-based snow is re-emitted to the atmosphere as gaseous elemental mercury, while a minor fraction (4%) of oxidized mercury that is deposited to sea ice is re-emitted during spring. Our work demonstrates that hourly differences in bromine/ozone chemistry in the atmosphere must be considered to capture the springtime Arctic mercury cycle, including its integration into the cryosphere and ocean.

Natural short-lived halogens exert an indirect cooling effect on climate

Saiz-Lopez A., Fernandez R. P., Li Q., Cuevas C. A., Fu X., Kinnison D. E., Tilmes S., Mahajan A. S., Martín Gómez J. C., Iglesias-Suarez F., Hossaini R., Plane J. M. C., Myhre G. and Lamarque J.-F.

Nature, 618, pages 967–973,, 2023.


Observational evidence shows the ubiquitous presence of ocean-emitted short-lived halogens in the global atmosphere1,2,3. Natural emissions of these chemical compounds have been anthropogenically amplified since pre-industrial times4,5,6, while, in addition, anthropogenic short-lived halocarbons are currently being emitted to the atmosphere7,8. Despite their widespread distribution in the atmosphere, the combined impact of these species on Earth’s radiative balance remains unknown. Here we show that short-lived halogens exert a substantial indirect cooling effect at present (−0.13 ± 0.03 watts per square metre) that arises from halogen-mediated radiative perturbations of ozone (−0.24 ± 0.02 watts per square metre), compensated by those from methane (+0.09 ± 0.01 watts per square metre), aerosols (+0.03 ± 0.01 watts per square metre) and stratospheric water vapour (+0.011 ± 0.001 watts per square metre). Importantly, this substantial cooling effect has increased since 1750 by −0.05 ± 0.03 watts per square metre (61 per cent), driven by the anthropogenic amplification of natural halogen emissions, and is projected to change further (18–31 per cent by 2100) depending on climate warming projections and socioeconomic development. We conclude that the indirect radiative effect due to short-lived halogens should now be incorporated into climate models to provide a more realistic natural baseline of Earth’s climate system.

Photocatalytic chlorine atom production on mineral dust–sea spray aerosols over the North Atlantic

Maarten M. J. W. van Herpen, Qinyi Li, Alfonso Saiz- Lopez, Jesper B. Liisberg, Thomas Röckmann, Carlos A. Cuevas, Rafael P. Fernandez, John E. Mak, Natalie M. Mahowald, Peter Hess, Daphne Meidan, Jan- Berend W. Stuutj and Matthew S. Johnson.

PNAS 2023 Vol. 120 No. 31 e2303974120, 2023.


Active chlorine in the atmosphere is poorly constrained and so is its role in the oxidation of the potent greenhouse gas methane, causing uncertainty in global methane budgets. We propose a photocatalytic mechanism for chlorine atom production that occurs when Sahara dust mixes with sea spray aerosol. The mechanism is validated by implementation in a global atmospheric model and thereby explaining the episodic, seasonal, and location-dependent 13C depletion in CO in air samples from Barbados [J.E. Mak, G. Kra, T. Sandomenico, P. Bergamaschi, J. Geophys. Res. Atmos. 108 (2003)], which remained unexplained for decades. The production of Cl can also explain the anomaly in the CO:ethane ratio found at Cape Verde [K. A. Read et al., J. Geophys. Res. Atmos. 114 (2009)], in addition to explaining the observation of elevated HOCl [M. J. Lawler et al., Atmos. Chem. Phys. 11, 7617–7628 (2011)]. Our model finds that 3.8 Tg(Cl) y−1 is produced over the North Atlantic, making it the dominant source of chlorine in the region; globally, chlorine production increases by 41%. The shift in the methane sink budget due to the increased role of Cl means that isotope-constrained top–down models fail to allocate 12 Tg y−1 (2% of total methane emissions) to 13C-depleted biological sources such as agriculture and wetlands. Since 2014, an increase in North African dust emissions has increased the 13C isotope of atmospheric CH4, thereby partially masking a much greater decline in this isotope, which has implications for the interpretation of the drivers behind the recent increase of methane in the atmosphere.

Potential Stratospheric Ozone Depletion Due To Iodine Injection From Small Satellites

Wuhu Feng, John M. C. Plane, Martyn P. Chipperfield, Alfonso Saiz-Lopez and Jean-Paul Booth.

Geophysical Research Letters, 50, e2022GL102300,, 2023.


We use the 3-D Whole Atmospheric Community Climate Model to investigate stratospheric ozone depletion due to the launch of small satellites (e.g., CubeSats) with an iodine propulsion system. The model considers the injection of iodine from the satellites into the Earth's thermosphere and suggests a 4-yr timescale for transport of the emissions down to the troposphere. The base case scenario is 40,000 small satellite launches per year into low orbit (100–600 km), which would inject 8 tons I yr−1 above 120 km as I+ ions and increase stratospheric inorganic iodine by ∼0.1 part per trillion (pptv). The model shows that this scenario produces a negligible impact on global stratospheric ozone (∼0.05 DU column depletion). In contrast, a 100-fold increase in the launch rate, and therefore thermospheric iodine injection, is predicted to result in modeled ozone depletion of up to 14 DU (approximately 2%–7%) over the polar regions.

Sea2Cloud: From Biogenic Emission Fluxes to Cloud Properties in the Southwest Pacific

Karine Sellegri, Mike Harvey, Maija Peltola, Alexia Saint-Macary, Theresa Barthelmeß, Manon Rocco, Kathryn A. Moore, Antonia Cristi, Frederic Peyrin, Neill Barr, Laurent Labonnote, Andrew Marriner, John McGregor, Karl Safi, Stacy Deppeler, Stephen Archer, Erin Dunne, James Harnwell, Julien Delanoe, Evelyn Freney, Clémence Rose, Clément Bazantay, Céline Planche, Alfonso Saiz-Lopez, Jesús E. Quintanilla-López, Rosa Lebrón-Aguilar, Matteo Rinaldi, Sandra Banson, Romain Joseph, Aurelia Lupascu, Olivier Jourdan, Guillaume Mioche, Aurélie Colomb, Gus Olivares, Richard Querel, Adrian McDonald, Graeme Plank, Beata Bukosa, Wayne Dillon, Jacques Pelon, Jean-Luc Baray, Frederic Tridon, Franck Donnadieu, Frédéric Szczap, Anja Engel, Paul J. DeMott and Cliff S. Law.

Bulletin of the American Meteorological Society, Volume 104, Issue 5, pages: E1017–E1043,, 2023


The goal of the Sea2Cloud project is to study the interplay between surface ocean biogeochemical and physical properties, fluxes to the atmosphere, and ultimately their impact on cloud formation under minimal direct anthropogenic influence. Here we present an interdisciplinary approach, combining atmospheric physics and chemistry with marine biogeochemistry, during a voyage between 41° and 47°S in March 2020. In parallel to ambient measurements of atmospheric composition and seawater biogeochemical properties, we describe semicontrolled experiments to characterize nascent sea spray properties and nucleation from gas-phase biogenic emissions. The experimental framework for studying the impact of the predicted evolution of ozone concentration in the Southern Hemisphere is also detailed. After describing the experimental strategy, we present the oceanic and meteorological context including provisional results on atmospheric thermodynamics, composition, and flux measurements. In situ measurements and flux studies were carried out on different biological communities by sampling surface seawater from subantarctic, subtropical, and frontal water masses. Air–Sea-Interface Tanks (ASIT) were used to quantify biogenic emissions of trace gases under realistic environmental conditions, with nucleation observed in association with biogenic seawater emissions. Sea spray continuously generated produced sea spray fluxes of 34% of organic matter by mass, of which 4% particles had fluorescent properties, and which size distribution resembled the one found in clean sectors of the Southern Ocean. The goal of Sea2Cloud is to generate realistic parameterizations of emission flux dependences of trace gases and nucleation precursors, sea spray, cloud condensation nuclei, and ice nuclei using seawater biogeochemistry, for implementation in regional atmospheric models.

Sensitivity of tropospheric ozone to halogen chemistry in the chemistry–climate model LMDZ-INCA vNMHC

Cyril Caram, Sophie Szopa, Anne Cozic, Slimane Bekki, Carlos A. Cuevas and Alfonso Saiz-Lopez.

Geoscice Model Development, 16, 4041–4062, 2023,, 2023.


The atmospheric chemistry of halogenated species (Cl, Br, I) participates in the global chemical sink of tropospheric ozone and perturbs the oxidising capacity of the troposphere, notably by influencing the atmospheric lifetime of methane. Global chemistry–climate models are commonly used to assess the global budget of ozone and its sensitivity to emissions of its precursors, as well as to project its long-term evolution. Here, we report on the implementation of tropospheric sources and chemistry of halogens in the chemistry–climate model LMDZ-INCA (Laboratoire de Météorologie Dynamique general circulation model, LMDZ, and Interactions with Chemistry and Aerosols, INCA, version with Non-Methane HydroCarbon chemistry, vNMHC) and evaluate halogen effects on the tropospheric ozone budget. Overall, the results show that the model simulates satisfactorily the impact of halogens on the photo-oxidising system in the troposphere, in particular in the marine boundary layer. To quantify the effects of halogen chemistry in LMDZ-INCA, standard metrics representative of the behaviour of the tropospheric chemical system (Ox, HOx, NOx, CH4 and non-methane volatile organic compounds – NMVOCs) are computed with and without halogens. The addition of tropospheric halogens in the LMDZ-INCA model leads to a decrease of 22 % in the ozone burden, 8 % in OH and 33 % in NOx. Sensitivity simulations show for the first time that the inclusion of halogen chemistry makes ozone more sensitive to perturbations in CH4, NOx and NMVOCs. Consistent with other global model studies, the sensitivity of the tropospheric ozone burden to changes from pre-industrial to present-day emissions is found to be ∼20 % lower when tropospheric halogens are taken into account.

Significant Impact of Reactive Chlorine on Complex Air Pollution Over the Yangtze River Delta Region, China

Xin Yi, Golam Sarwar, Jinting Bian, Ling Huang, Qinyi Li, Sen Jiang, Hanqing Liu, Yangjun Wang, Hui Chen, Tao Wang, Jianmin Chen, Alfonso Saiz-Lopez, David C. Wong and Li Li

Journal of Geophysical Research: Atmospheres, 128, e2023JD038898., 2023


The chlorine radical (Cl) plays a crucial role in the formation of secondary air pollutants by determining the total atmospheric oxidative capacity (AOC). However, there are still large discrepancies among studies on chlorine chemistry, mainly due to uncertainties from three aspects: (a) Anthropogenic emissions of reactive chlorine species from disinfectant usage are typically overlooked. (b) The heterogeneous reaction uptake coefficients used in air quality models resulted in certain differences. (c) The co-effect of anthropogenic and natural emissions is rarely investigated. In this study, the Weather Research and Forecasting (WRF)-Community Multiscale Air Quality (CMAQ) modeling system (updated with 21 new reactions and a comprehensive emissions inventory) was used to simulate the combined impact of chlorine emissions on the air quality of a coastal city cluster in the Yangtze River Delta (YRD) region. The results indicate that the new emissions of reactive chlorine and the updated gas-phase and heterogeneous chlorine chemistry can significantly enhance the AOC by 21.3%, 8.7%, 43.3%, and 58.7% in spring, summer, autumn, and winter, respectively. This is more evident in inland areas with high Cl concentrations. Our updates to the chlorine chemistry also increases the monthly mean maximum daily 8-hr average (MDA 8) O3 mixing ratio by 4.1–7.0 ppbv in different seasons. Additionally, chlorine chemistry promotes the formation of fine particulate matter (PM2.5), with maximum monthly average enhancements of 4.7–13.3 μg/m3 in different seasons. This study underlines the significance of adding full chlorine emissions and updating chlorine chemistry in air quality models, and demonstrates that chlorine chemistry may significantly impact air quality over coastal regions.

The diverse meteorology of Jezero crater over the first 250 sols of Perseverance on Mars

J. A. Rodriguez-Manfredi, M. de la Torre Juarez, A. Sanchez-Lavega, R. Hueso, G. Martinez, M. T. Lemmon, C. E. Newman, A. Munguira, M. Hieta, L. K. Tamppari, J. Polkko, D. Toledo, E. Sebastian, M. D. Smith, I. Jaakonaho, M. Genzer, A. De Vicente-Retortillo, D. Viudez-Moreiras, M. Ramos, A. Saiz-Lopez, A. Lepinette, M. Wolff, R. J. Sullivan, J. Gomez-Elvira, V. Apestigue, P. G. Conrad, T. Del Rio-Gaztelurrutia, N. Murdoch, I. Arruego, D. Banfield, J. Boland, A. J. Brown, J. Ceballos, M. Dominguez-Pumar, S. Espejo, A. G. Fairén, R. Ferrandiz, E. Fischer, M. Garcia-Villadangos, S. Gimenez, F. Gomez-Gomez, S. D. Guzewich, A.-M. Harri, J. J. Jimenez, V. Jimenez, T. Makinen, M. Marin, C. Martin, J. Martin-Soler, A. Molina, L. Mora-Sotomayor, S. Navarro, V. Peinado, I. Perez-Grande, J. Pla-Garcia, M. Postigo, O. Prieto-Ballesteros, S. C. R. Rafkin, M. I. Richardson, J. Romeral, C. Romero, H. Savijärvi, J. T. Schofield, J. Torres, R. Urqui, S. Zurita & the MEDA team*.

Nature Geoscience 16, 19–28,, 2023.


NASA’s Perseverance rover’s Mars Environmental Dynamics Analyzer is collecting data at Jezero crater, characterizing the physical processes in the lowest layer of the Martian atmosphere. Here we present measurements from the instrument’s first 250 sols of operation, revealing a spatially and temporally variable meteorology at Jezero. We find that temperature measurements at four heights capture the response of the atmospheric surface layer to multiple phenomena. We observe the transition from a stable night-time thermal inversion to a daytime, highly turbulent convective regime, with large vertical thermal gradients. Measurement of multiple daily optical depths suggests aerosol concentrations are higher in the morning than in the afternoon. Measured wind patterns are driven mainly by local topography, with a small contribution from regional winds. Daily and seasonal variability of relative humidity shows a complex hydrologic cycle. These observations suggest that changes in some local surface properties, such as surface albedo and thermal inertia, play an influential role. On a larger scale, surface pressure measurements show typical signatures of gravity waves and baroclinic eddies in a part of the seasonal cycle previously characterized as low wave activity. These observations, both combined and simultaneous, unveil the diversity of processes driving change on today’s Martian surface at Jezero crater.

Very short-lived halogens amplify ozone depletion trends in the tropical lower stratosphere

Villamayor, J., Iglesias-Suarez, F., Cuevas, C. A., Fernandez, R. P., Li, Q., Abalos, M., Hossaini, R., Chipperfield, M. P., Kinnison, D. E., Tilmes, S., Lamarque, J.-F. and Saiz-Lopez, A.

Nature Climate Change, DOI:10.1038/s41558-023-01671-y , 2023.


In contrast to the general stratospheric ozone recovery following international agreements, recent observations show an ongoing net ozone depletion in the tropical lower stratosphere (LS). This depletion is thought to be driven by dynamical transport accelerated by global warming, while chemical processes have been considered to be unimportant. Here we use a chemistry–climate model to demonstrate that halogenated ozone-depleting very short-lived substances (VSLS) chemistry may account for around a quarter of the observed tropical LS negative ozone trend in 1998–2018. VSLS sources include both natural and anthropogenic emissions. Future projections show the persistence of the currently unaccounted for contribution of VSLS to ozone loss throughout the twenty-first century in the tropical LS, the only region of the global stratosphere not projecting an ozone recovery by 2100. Our results show the need for mitigation strategies of anthropogenic VSLS emissions to preserve the present and future ozone layer in low latitudes.

Widespread detection of chlorine oxyacids in the Arctic atmosphere

Yee Jun Tham, Nina Sarnela, Siddharth Iyer, Qinyi Li, Hélène Angot, Lauriane L. J. Quéléver, Ivo Beck, Tiia Laurila, Lisa J. Beck, Matthew Boyer, Javier Carmona-García, Ana Borrego-Sánchez, Daniel Roca-Sanjuán, Otso Peräkylä, Roseline C. Thakur, Xu-Cheng He, Qiaozhi Zha, Dean Howard, Byron Blomquist, Stephen D. Archer, Ludovic Bariteau, Kevin Posman, Jacques Hueber, Detlev Helmig, Hans-Werner Jacobi, Heikki Junninen, Markku Kulmala, Anoop S. Mahajan, Andreas Massling, Henrik Skov, Mikko Sipilä, Joseph S. Francisco, Julia Schmale, Tuija Jokinen and Alfonso Saiz-Lopez.

Nature Communications, volume 14, Article number: 1769,, 2023.


Chlorine radicals are strong atmospheric oxidants known to play an important role in the depletion of surface ozone and the degradation of methane in the Arctic troposphere. Initial oxidation processes of chlorine produce chlorine oxides, and it has been speculated that the final oxidation steps lead to the formation of chloric (HClO3) and perchloric (HClO4) acids, although these two species have not been detected in the atmosphere. Here, we present atmospheric observations of gas-phase HClO3 and HClO4. Significant levels of HClO3 were observed during springtime at Greenland (Villum Research Station), Ny-Ålesund research station and over the central Arctic Ocean, on-board research vessel Polarstern during the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC) campaign, with estimated concentrations up to 7 × 106 molecule cm−3. The increase in HClO3, concomitantly with that in HClO4, was linked to the increase in bromine levels. These observations indicated that bromine chemistry enhances the formation of OClO, which is subsequently oxidized into HClO3 and HClO4 by hydroxyl radicals. HClO3 and HClO4 are not photoactive and therefore their loss through heterogeneous uptake on aerosol and snow surfaces can function as a previously missing atmospheric sink for reactive chlorine, thereby reducing the chlorine-driven oxidation capacity in the Arctic boundary layer. Our study reveals additional chlorine species in the atmosphere, providing further insights into atmospheric chlorine cycling in the polar environment.

Year-long ground-based observations of bromine oxide over Bharati Station, Antarctica.

Shrutika P. Wagh, Sankirna D. Joge, Surendra Singh, Prithviraj Mali, Steffen Beirle, Thomas Wagner, Silvia Bucci, Alfonso Saiz-Lopez, Rohini Bhawar, Anoop S. Mahajan.

Polar Science,, 2023.


Bromine chemistry plays an important role in tropospheric ozone depletion events in polar regions. Autocatalytic reactions lead to bromine explosion events, causing ozone depletion to near-zero levels in the polar troposphere. Bromine chemistry over Antarctica is not fully understood, and ground-based observations are scarce. This work presents year-long observations of bromine oxide (BrO) over the Bharati station (69.41°S, 76.19°E) using Multi-axis Differential Optical Absorption Spectroscopy (MAX-DOAS) from December 2018 to February 2020. The results show that elevated BrO mixing ratios were found during spring (September), with a maximum value of 10.21 ± 4.38 pptv for clear sky conditions and 33.15 ± 2.23 pptv for cloudy conditions. BrO was not observed above the detection limit (∼3 × 1013 molecule cm−2) outside spring on clear days. In general, lower mixing ratios were observed on clear days over Bharati compared to stations in West Antarctica. This indicates a different source strength over East Antarctica compared to West Antarctica. BrO vertical column densities were high during spring, with a maximum value of 1.34 ± 0.35 × 1014 molecule cm−2. The vertical profiles of the BrO mixing ratios show a peak at the surface during spring (average of 6.5 ± 1.91 pptv), decreasing sharply with altitude. Back trajectories show that air masses passing over the first year ice showed higher BrO, although factors such as meteorology play an important role in determining the absolute levels. Using a box model, we show that bromine chemistry can deplete as much as 2.15 ppb of ozone in a day at the Bharati Station on clear days, which shows that it does not lead to complete ozone depletion events over Bharati.

Climate changes modulated the history of Arctic iodine during the Last Glacial Cycle

Juan Pablo Corella, Niccolo Maffezzoli, Andrea Spolaor, Paul Vallelonga, Carlos A. Cuevas, Federico Scoto, Juliane Müller, Bo Vinther, Helle A. Kjær, Giulio Cozzi, Ross Edwards, Carlo Barbante & Alfonso Saiz-Lopez

Nature Communications volume 13, Article number: 88,, 2022.


Iodine has a significant impact on promoting the formation of new ultrafine aerosol particles and accelerating tropospheric ozone loss, thereby affecting radiative forcing and climate. Therefore, understanding the long-term natural evolution of iodine, and its coupling with climate variability, is key to adequately assess its effect on climate on centennial to millennial timescales. Here, using two Greenland ice cores (NEEM and RECAP), we report the Arctic iodine variability during the last 127,000 years. We find the highest and lowest iodine levels recorded during interglacial and glacial periods, respectively, modulated by ocean bioproductivity and sea ice dynamics. Our sub-decadal resolution measurements reveal that high frequency iodine emission variability occurred in pace with Dansgaard/Oeschger events, highlighting the rapid Arctic ocean-ice-atmosphere iodine exchange response to abrupt climate changes. Finally, we discuss if iodine levels during past warmer-than-present climate phases can serve as analogues of future scenarios under an expected ice-free Arctic Ocean. We argue that the combination of natural biogenic ocean iodine release (boosted by ongoing Arctic warming and sea ice retreat) and anthropogenic ozone-induced iodine emissions may lead to a near future scenario with the highest iodine levels of the last 127,000 years.

Full latitudinal marine atmospheric measurements of iodine monoxide

Hisahiro Takashima, Yugo Kanaya, Saki Kato, Martina M. Friedrich, Michel Van Roozendael, Fumikazu Taketani, Takuma Miyakawa, Yuichi Komazaki, Carlos A. Cuevas, Alfonso Saiz-Lopez and Takashi Sekiya

Atmos. Chem. Phys., 22, 4005–4018,


Iodine compounds destroy ozone (O3) in the global troposphere and form new aerosols, thereby affecting the global radiative balance. However, few reports have described the latitudinal distribution of atmospheric iodine compounds. This work reports iodine monoxide (IO) measurements taken over unprecedented sampling areas from the Arctic to the Southern Hemisphere and spanning sea surface temperatures (SSTs) of approximately 0 to 31.5 ∘C. The highest IO concentrations were observed over the Western Pacific warm pool (WPWP), where O3 minima were also measured. There, a negative correlation was found between O3 and IO mixing ratios at extremely low O3 concentrations. This correlation is not explained readily by the O3-dependent oceanic fluxes of photolabile inorganic iodine compounds, which is the dominant source in recent global-scale chemistry transport models representing iodine chemistry. Actually, the correlation rather implies that O3-independent pathways can be similarly important in the WPWP. The O3-independent fluxes result in a 15 % greater O3 loss than that estimated for O3-dependent processes alone. The daily O3 loss rate related to iodine over the WPWP is as high as approximately 2 ppbv (parts per billion by volume) despite low O3 concentrations of approximately 10 ppbv, with the loss being up to 100 % greater than that without iodine. This finding suggests that warming SST driven by climate change might affect the marine atmospheric chemical balance through iodine–ozone chemistry


Global seasonal distribution of CH2Br2 and CHBr3 in the upper troposphere and lower stratosphere

Markus Jesswein, Rafael P. Fernandez, Lucas Berná, Alfonso Saiz-Lopez, Jens-Uwe Grooß, Ryan Hossaini, Eric C. Apel, Rebecca S. Hornbrook, Elliot L. Atlas, Donald R. Blake, Stephen Montzka, Timo Keber, Tanja Schuck, Thomas Wagenhäuser and Andreas Engel.

Atmos. Chem. Phys., 22, 15049–15070,, 2022.


Bromine released from the decomposition of short-lived brominated source gases contributes as a sink of ozone in the lower stratosphere. The two major contributors are CH2Br2 and CHBr3. In this study, we investigate the global seasonal distribution of these two substances, based on four High Altitude and Long Range Research Aircraft (HALO) missions, the HIAPER Pole-to-Pole Observations (HIPPO) mission, and the Atmospheric Tomography (ATom) mission. Observations of CH2Br2 in the free and upper troposphere indicate a pronounced seasonality in both hemispheres, with slightly larger mixing ratios in the Northern Hemisphere (NH). Compared to CH2Br2, CHBr3 in these regions shows larger variability and less clear seasonality, presenting larger mixing ratios in winter and autumn in NH midlatitudes to high latitudes. The lowermost stratosphere of SH and NH shows a very similar distribution of CH2Br2 in hemispheric spring with differences well below 0.1 ppt, while the differences in hemispheric autumn are much larger with substantially smaller values in the SH than in the NH. This suggests that transport processes may be different in both hemispheric autumn seasons, which implies that the influx of tropospheric air (“flushing”) into the NH lowermost stratosphere is more efficient than in the SH. The observations of CHBr3 support the suggestion, with a steeper vertical gradient in the upper troposphere and lower stratosphere in SH autumn than in NH autumn. However, the SH database is insufficient to quantify this difference. We further compare the observations to model estimates of TOMCAT (Toulouse Off-line Model of Chemistry And Transport) and CAM-Chem (Community Atmosphere Model with Chemistry, version 4), both using the same emission inventory of Ordóñez et al. (2012). The pronounced tropospheric seasonality of CH2Br2 in the SH is not reproduced by the models, presumably due to erroneous seasonal emissions or atmospheric photochemical decomposition efficiencies. In contrast, model simulations of CHBr3 show a pronounced seasonality in both hemispheres, which is not confirmed by observations. The distributions of both species in the lowermost stratosphere of the Northern and Southern hemispheres are overall well captured by the models with the exception of southern hemispheric autumn, where both models present a bias that maximizes in the lowest 40 K above the tropopause, with considerably lower mixing ratios in the observations. Thus, both models reproduce equivalent flushing in both hemispheres, which is not confirmed by the limited available observations. Our study emphasizes the need for more extensive observations in the SH to fully understand the impact of CH2Br2 and CHBr3 on lowermost-stratospheric ozone loss and to help constrain emissions.

Insights into the Chemistry of Iodine New Particle Formation: The Role of Iodine Oxides and the Source of Iodic Acid

Juan Carlos Gómez Martín, Thomas R. Lewis, Alexander D. James, Alfonso Saiz-Lopez and John M. C. Plane

J. Am. Chem. Soc.,


Iodine chemistry is an important driver of new particle formation in the marine and polar boundary layers. There are, however, conflicting views about how iodine gas-to-particle conversion proceeds. Laboratory studies indicate that the photooxidation of iodine produces iodine oxides (IxOy), which are well-known particle precursors. By contrast, nitrate anion chemical ionization mass spectrometry (CIMS) observations in field
and environmental chamber studies have been interpreted as evidence of a dominant role of iodic acid (HIO 3) in iodine-driven particle formation. Here, we report flow tube laboratory experiments that solve these discrepancies by showing that both IxOy and HIO3 are involved in atmospheric new particle formation. I 2Oy molecules (y = 2, 3, and 4) react with nitrate core ions to generate mass spectra similar to those obtained by CIMS, including the iodate anion. Iodine pentoxide (I2 O5 ) produced by photolysis of higher-order IxOy is hydrolyzed, likely by the water dimer, to yield HIO3 , which also contributes to the iodate anion signal. We estimate that ∼50% of the iodate anion signals observed by nitrate CIMS under atmospheric water vapor concentrations originate from I 2Oy. Under such conditions, iodine-containing clusters and particles are formed by aggregation of I 2 Oy and HIO3 , while under dry laboratory conditions, particle formation is driven exclusively by I 2Oy. An updated mechanism for iodine gas-to-particle conversion is provided. Furthermore, we propose that a key iodine reservoir species such as iodine nitrate, which we observe as a product of the reaction between iodine oxides and the nitrate anion, can also be detected by CIMS in the atmosphere.


Mixing state and distribution of iodine-containing particles in Arctic Ocean during summertime

Longquan Wang, Jinpei Yan, Alfonso Saiz-Lopez, Bei Jiang, Fange Yue, Xiawei Yu, Zhouqing Xie.

Science of The Total Environment, Volume 834, 155030,, 2022.


Iodine chemistry plays a key role in ozone destruction and new aerosol formation in the marine boundary layer (MBL), especially in polar regions. We investigated iodine-containing particles (0.2-2 μm) in the Arctic Ocean using a ship-based single particle aerosol mass spectrometer from July to August 2017. Seven main particle types were identified: dust, biomass combustion particles, sea salt, organic S, aromatics, hydrocarbon-like compounds, and amines. The number fraction of iodine-containing particles was higher inside the Arctic Circle (>65°N) than outside (55–65°N). According to the air mass back trajectories, the latitudinal distribution of iodine-containing particles can be mainly attributed to iodine emissions from the sea ice edge region. Diurnal trends were found, especially during the second half of cruise, with peak iodine-containing particle number fractions during low-light conditions and relatively low number fractions at midday. These results imply that solar radiation plays a significant role in modulating particulate iodine in the Arctic atmosphere.


New processing methodology to incorporate marine halocarbons and dimethyl sulfide (DMS) emissions from the CAMS-GLOB-OCE dataset in air quality modeling studies

Ernesto Pino‑Cortés, Katherine Gómez, Fernando González Taboada, Joshua S. Fu, Alfonso Saiz‑Lopez and Juan Höfer.

Air Quality, Atmosphere & Health,, 2023.


Oceans are the largest source of biogenic emissions to the atmosphere, including aerosol precursors like marine halocarbons and dimethyl sulfide (DMS). During the last decade, the CAMS-GLOB-OCE dataset has developed an analysis of daily emissions of tribromomethane (CHBr3), dibromomethane (CH2Br2), iodomethane (CH3I), and DMS, due to its increasingly recognized role on tropospheric chemistry and climate dynamics. The potential impacts of these compounds on air quality modeling remain, however, largely unexplored. The lack of a reliable and easy methodology to incorporate these marine emissions into air quality models is probably one of the reasons behind this knowledge gap. Therefore, this study describes a methodology to adapt the CAMS-GLOB-OCE dataset to be used as an input of the preprocessor software Sparse Matrix Operator Kernel Emissions (SMOKE). The method involves nine steps to update file attribute properties and to bilinearly interpolate compound emission fields. The procedure was tested using halocarbon and DMS emissions fields available within the CAMS-GLOB-OCE database for the Southern Ocean around Antarctica. We expect that this methodology will allow more studies to include the marine emissions of halocarbons and DMS in air quality studies.

On the Speciation of Iodine in Marine Aerosol

Juan Carlos Gómez Martín, Alfonso Saiz-Lopez, Carlos A. Cuevas, Alex R. Baker, and Rafael P. Fernández.

Journal of Geophysical Research: Atmospheres, 127, e2021JD036081,, 2022.


We have compiled and analyzed a comprehensive data set of field observations of iodine speciation in marine aerosol. The soluble iodine content of fine aerosol (PM1) is dominated by soluble organic iodine (SOI; ∼50%) and iodide (∼30%), while the coarse fraction is dominated by iodate (∼50%), with nonnegligible amounts of iodide (∼20%). The SOI fraction shows an equatorial maximum and minima coinciding with the ocean “deserts,” which suggests a link between soluble iodine speciation in aerosol and ocean productivity. Among the major aerosol ions, organic anions and non-sea-salt sulfate show positive correlations with SOI in PM1. Alkali cations are positively correlated to iodate and negatively correlated with SOI and iodide in coarse aerosol. These relationships suggest that under acidic conditions iodate is reduced to HOI, which reacts with organic matter to form SOI, a possible source of iodide. In less acidic sea-salt or dust-rich coarse aerosols, HOI oxidation to iodate and reaction with organic matter likely compete.



Photochemical and thermochemical pathways to S2 and polysulfur formation in the atmosphere of Venus

Antonio Francés-Monerris, Javier Carmona-García, Tarek Trabelsi, Alfonso Saiz-Lopez, James R. Lyons, Joseph S. Francisco and Daniel Roca-Sanjuán.

Nature Communication 13, 4425 (2022)., 2022.


Polysulfur species have been proposed to be the unknown near-UV absorber in the atmosphere of Venus. Recent work argues that photolysis of one of the (SO)2 isomers, cis-OSSO, directly yields S2 with a branching ratio of about 10%. If correct, this pathway dominates polysulfur formation by several orders of magnitude, and by addition reactions yields significant quantities of S3, S4, and S8. We report here the results of high-level ab-initio quantum-chemistry computations that demonstrate that S2 is not a product in cis-OSSO photolysis. Instead, we establish a novel mechanism in which S2 is formed in a two-step process. Firstly, the intermediate S2O is produced by the coupling between the S and Cl atmospheric chemistries (in particular, SO reaction with ClS) and in a lesser extension by O-abstraction reactions from cis-OSSO. Secondly, S2O reacts with SO. This modified chemistry yields S2 and subsequent polysulfur abundances comparable to the photolytic cis-OSSO mechanism through a more plausible pathway. Ab initio quantification of the photodissociations at play fills a critical data void in current atmospheric models of Venus.

Photodissociation of particulate nitrate as a source of daytime tropospheric Cl2

Xiang Peng, Tao Wang, Weihao Wang , A. R. Ravishankara, Christian George, Men Xia, Min Cai, Qinyi Li, Christian Mark Salvador, Chiho Lau, Xiaopu Lyu, Chun Nan Poon, Abdelwahid Mellouki, Yujing Mu, Mattias Hallquist, Alfonso Saiz-Lopez, Hai Guo, Hartmut Herrmann, Chuan Yu, Jianing Dai, Yanan Wang, Xinke Wang, Alfred Yu, Kenneth Leung, Shuncheng Lee and Jianmin Chen.

Nature Communications volume 13, Article number: 939 (2022),, 2022.


Chlorine atoms (Cl) are highly reactive and can strongly influence the abundances of climate and air quality-relevant trace gases. Despite extensive research on molecular chlorine (Cl2), a Cl precursor, in the polar atmosphere, its sources in other regions are still poorly understood. Here we report the daytime Cl2 concentrations of up to 1 ppbv observed in a coastal area of Hong Kong, revealing a large daytime source of Cl2 (2.7 pptv s−1 at noon). Field and laboratory experiments indicate that photodissociation of particulate nitrate by sunlight under acidic conditions (pH < 3.0) can activate chloride and account for the observed daytime Cl2 production. The high Cl2 concentrations significantly increased atmospheric oxidation. Given the ubiquitous existence of chloride, nitrate, and acidic aerosols, we propose that nitrate photolysis is a significant daytime chlorine source globally. This so far unaccounted for source of chlorine can have substantial impacts on atmospheric chemistry.



Radiation and Dust Sensor for Mars Environmental Dynamic Analyzer Onboard M2020 Rover

Victor Apestigue, Alejandro Gonzalo, Juan J. Jiménez, Justin Boland, Mark Lemmon, Jose R. de Mingo, Elisa García-Menendez, Joaquín Rivas, Joaquín Azcue, Laurent Bastide, Nuria Andrés-Santiuste, Javier Martínez-Oter, Miguel González-Guerrero, Alberto Martin-Ortega, Daniel Toledo, Francisco Javier Alvarez-Rios, Felipe Serrano , Boris Martín-Vodopivec, Javier Manzano, Raquel López Heredero, Isaías Carrasco, Sergio Aparicio, Ángel Carretero, Daniel R. MacDonald, Lori B. Moore, María Ángeles Alcacera, Jose A. Fernández-Viguri, Israel Martín, Margarita Yela, Maite Álvarez, Paula Manzano, Jose A. Martín, Juan C. del Hoyo, Manuel Reina, Roser Urqui, Jose A. Rodriguez-Manfredi, Manuel de la Torre Juárez, Christina Hernandez, Elizabeth Cordoba, Robin Leiter, Art Thompson, Soren Madsen, Michael D. Smith, Daniel Viúdez-Moreiras, Alfonso Saiz-Lopez, Agustín Sánchez-Lavega, Laura Gomez-Martín, Germán M. Martínez, Francisco J. Gómez-Elvira and Ignacio Arruego

Sernsors, 22, 2907,,2022.


The Radiation and Dust Sensor is one of six sensors of the Mars Environmental Dynamics Analyzer onboard the Perseverance rover from the Mars 2020 NASA mission. Its primary goal is to characterize the airbone dust in the Mars atmosphere, inferring its concentration, shape and optical properties. Thanks to its geometry, the sensor will be capable of studying dust-lifting processes with a high temporal resolution and high spatial coverage. Thanks to its multiwavelength design, it will characterize the solar spectrum from Mars’ surface. The present work describes the sensor design from the scientific and technical requirements, the qualification processes to demonstrate its endurance on Mars’ surface, the calibration activities to demonstrate its performance, and its validation campaign in a representative Mars analog. As a result of this process, we obtained a very compact sensor, fully digital, with a mass below 1 kg and exceptional power consumption and data budget features.


Reaction of SO3 with HONO2 and Implications for Sulfur Partitioning in the Atmosphere

Bo Long, Yu Xia, Junwei Lucas Bao, Javier Carmona-García, Juan Carlos Gómez Martín, John M. C. Plane, Alfonso Saiz-Lopez, Daniel Roca-Sanjuán and Joseph S. Francisco.

Journal of the American Chemical Society,, 2022.


Sulfur trioxide is a critical intermediate for the sulfur cycle and the formation of sulfuric acid in the atmosphere. The traditional view is that sulfur trioxide is removed by water vapor in the troposphere. However, the concentration of water vapor decreases significantly with increasing altitude, leading to longer atmospheric lifetimes of sulfur trioxide. Here, we utilize a dual-level strategy that combines transition state theory calculated at the W2X//DF-CCSD(T)-F12b/jun′-cc-pVDZ level, with variational transition state theory with small-curvature tunneling from direct dynamics calculations at the M08-HX/MG3S level. We also report the pressure-dependent rate constants calculated using the system-specific quantum Rice–Ramsperger–Kassel (SS-QRRK) theory. The present findings show that falloff effects in the SO3 + HONO2 reaction are pronounced below 1 bar. The SO3 + HONO2 reaction can be a potential removal reaction for SO3 in the stratosphere and for HONO2 in the troposphere, because the reaction can potentially compete well with the SO3 + 2H2O reaction between 25 and 35 km, as well as the OH + HONO2 reaction. The present findings also suggest an unexpected new product from the SO3 + HONO2 reaction, which, although very short-lived, would have broad implications for understanding the partitioning of sulfur in the stratosphere and the potential for the SO3 reaction with organic acids to generate organosulfates without the need for heterogeneous chemistry.


Reactive halogens increase the global methane lifetime and radiative forcing in the 21st century

Qinyi Li, Rafael P. Fernandez, Ryan Hossaini, Fernando Iglesias-Suarez, Carlos A. Cuevas, Eric C. Apel, Douglas E. Kinnison, Jean-François Lamarque & Alfonso Saiz-Lopez.

Nature Communications13:2768,, 2022


CH4 is the most abundant reactive greenhouse gas and a complete understanding of its atmospheric fate is needed to formulate mitigation policies. Current chemistry-climate models tend to underestimate the lifetime of CH4 , suggesting uncertainties in its sources and sinks. Reactive halogens substantially perturb the budget of tropospheric OH, the main CH 4 loss. However, such an effect of atmospheric halogens is not considered in existing climate projections of CH4 burden and radiative forcing. Here, we demonstrate that reactive halogen chemistry increases the global CH4 lifetime by 6–9% during the 21st century. This effect arises from significant halogen-mediated decrease, mainly by iodine and bromine, in OH-driven CH4 loss that surpasses the direct Cl-induced CH4 sink. This increase in CH 4 lifetime helps to reduce the gap between models and observations and results in a greater burden and radiative forcing during this century. The increase in CH 4 burden due to halogens (up to 700 Tg or 8% by 2100) is equivalent to the observed atmospheric CH 4 growth during the last three to four decades. Notably, the halogen-driven enhancement in CH 4 radiative forcing is 0.05 W/m 2 at present and is projected to increase in the future (0.06 W/m 2 by 2100); such enhancement equals ~10% of present-day CH4 radiative forcing and one-third of N2 O radiative forcing, the third-largest well-mixed greenhouse gas. Both direct (Cl-driven) and indirect (via OH) impacts of halogens should be included in future CH 4 projections.


Reproducing Arctic springtime tropospheric ozone and mercury depletion events in an outdoor mesocosm sea ice facility

Zhiyuan Gao, Nicolas-Xavier Geilfus, Alfonso Saiz-Lopez, and Feiyue Wang

Atmos. Chem. Phys., 22, 1811–1824,, 2022.


The episodic buildup of gas-phase reactive bromine species over sea ice and snowpack in the springtime Arctic plays an important role in boundary layer processes, causing annual concurrent depletion of ozone and gaseous elemental mercury (GEM) during polar sunrise. Extensive studies have shown that these phenomena, known as bromine explosion events (BEEs), ozone depletion events (ODEs), and mercury depletion events (MDEs) are all triggered by reactive bromine species that are photochemically activated from bromide via multi-phase reactions under freezing air temperatures. However, major knowledge gaps exist in both fundamental cryo-photochemical processes causing these events and meteorological conditions that may affect their timing and magnitude. Here, we report an outdoor mesocosm study in which we successfully reproduced ODEs and MDEs at the Sea-ice Environmental Research Facility (SERF) in Winnipeg, Canada. By monitoring ozone and GEM concentrations inside large acrylic tubes over bromide-enriched artificial seawater during sea ice freeze-and-melt cycles, we observed mid-day photochemical ozone and GEM loss in winter in the in-tube boundary layer air immediately above the sea ice surface in a pattern that is characteristic of BEE-induced ODEs and MDEs in the Arctic. The importance of UV radiation and the presence of a condensed phase (experimental sea ice or snow) in causing such reactions were demonstrated by comparing ozone and GEM concentrations between the UV-transmitting and UV-blocking acrylic tubes under different air temperatures. The ability of reproducing BEE-induced photochemical phenomena in a mesocosm in a non-polar region provides a new approach to systematically studying the cryo-photochemical processes and meteorological conditions leading to BEEs, ODEs, and MDEs in the Arctic, their role in biogeochemical cycles across the ocean–sea ice–atmosphere interface, and their sensitivities to climate change.



Role of Iodine Recycling on Sea-Salt Aerosols in the Global Marine Boundary Layer

Qinyi Li, Yee Jun Tham, Rafael P. Fernandez, Xu-Cheng He, Carlos A. Cuevas and Alfonso Saiz-Lopez

Geophysical Research Letters, 49, e2021GL097567., 2022.


Heterogeneous uptake of hypoiodous acid (HOI), the dominant inorganic iodine species in the marine boundary layer (MBL), on sea-salt aerosol (SSA) to form iodine monobromide and iodine monochloride has been adopted in models with assumed efficiency. Recently, field measurements have reported a much faster rate of this recycling process than previously assumed in models. Here, we conduct global model simulations to quantify the range of effects of iodine recycling within the MBL, using Conventional, Updated, and Upper-limit coefficients. When considering the Updated coefficient, iodine recycling significantly enhances gaseous inorganic iodine abundance (∼40%), increases halogen atom production rates (∼40% in I, >100% in Br, and ∼60% in Cl), and reduces oxidant levels (−7% in O3, −2% in OH, and −4% in HO2) compared to the simulation without the process. We appeal for further direct measurements of iodine species, laboratory experiments on the controlling factors, and multiscale simulations of iodine heterogeneous recycling.



Saharan air outflow variability in the 1980–2020 period

Jose A. Adame, Alberto Notario, Carlos A. Cuevas, Alfonso Saiz-Lopez

Science of The Total Environment, Volume 839, 156268,, 2022


Airborne dust represents a hazard to the environment and human health. The outflow of air masses carrying dust from northern Africa, the world's largest active dust source, to the North Atlantic and Mediterranean regions is modulated by atmospheric conditions. However, how global warming-driven changes on atmospheric circulation have influenced North African air outflow in the recent past is not well understood. Here, we explore the Saharan air outflow from northwestern Africa over the 1980 to 2020 period. We find a decrease in the transport to the Atlantic Ocean and the Iberian Peninsula of −0.29 ± 0.16% dec−1 and -0.66 ± 0.18% dec−1, respectively, and an increasing trend to the Mediterranean Sea (0.24 ± 0.18% dec−1) and Europe (0.60 ± 0.18% dec−1). The results indicate that the strengthening of the Atlantic high pressure system and the Saharan thermal low, both associated with the narrowing of the Intertropical Convergence Zone and the Hadley Cell expansion under global warming, could be favoring the Saharan outflow to the Mediterranean Sea and Europe in detriment of transport to the Atlantic Ocean. The results also show that present-day Saharan air arrives at these regions at higher altitudes and in shorter timescales than decades ago. This is associated to the increase in surface heating conditions in the Sahara, 0.41 ± 0.02 °C dec−1, that can inject air into windier upper atmospheric levels, thereby allowing higher and faster air transport. Our results suggest a change in the Saharan air outflow likely associated with global warming and with potentially significant implications for the temporal and spatial patterns of North African dust export.


Sea ice fluctuations in the Baffin Bay and the Labrador Sea during glacial abrupt climate changes.

Federico Scoto, Henrik Sadatzki, Niccolo Maffezzoli, Carlo Barbante, Alessandro Gagliardi, Cristiano Varin, Paul Vallelonga, Vasileios Gkinis, Dorthe Dahl-Jensen, Helle Astrid Kjær, Francois Burgay, Alfonso Saiz-Lopez, Ruediger Stein and Andrea Spolaor

PNAS Vol. 119, No. 44, e2203468119, 2022.


Sea ice decline in the North Atlantic and Nordic Seas has been proposed to contribute to the repeated abrupt atmospheric warmings recorded in Greenland ice cores during the last glacial period, known as Dansgaard-Oeschger (D-O) events. However, the understanding of how sea ice changes were coupled with abrupt climate changes during D-O events has remained incomplete due to a lack of suitable high-resolution sea ice proxy records from northwestern North Atlantic regions. Here, we present a subdecadal-scale bromine enrichment (Brenr) record from the NEEM ice core (Northwest Greenland) and sediment core biomarker records to reconstruct the variability of seasonal sea ice in the Baffin Bay and Labrador Sea over a suite of D-O events between 34 and 42 ka. Our results reveal repeated shifts between stable, multiyear sea ice (MYSI) conditions during cold stadials and unstable, seasonal sea ice conditions during warmer interstadials. The shift from stadial to interstadial sea ice conditions occurred rapidly and synchronously with the atmospheric warming over Greenland, while the amplitude of high-frequency sea ice fluctuations increased through interstadials. Our findings suggest that the rapid replacement of widespread MYSI with seasonal sea ice amplified the abrupt climate warming over the course of D-O events and highlight the role of feedbacks associated with late-interstadial seasonal sea ice expansion in driving the North Atlantic ocean–climate system back to stadial conditions.

Substantial contribution of iodine to Arctic ozone destruction

Nuria Benavent, Anoop S. Mahajan, Qinyi Li, Carlos A. Cuevas, Julia Schmale, Hélène Angot, Tuija Jokinen, Lauriane L. J. Quéléver, Anne-Marlene Blechschmidt, Bianca Zilker, Andreas Richter, Jesús A. Serna, David Garcia-Nieto, Rafael P. Fernandez, Henrik Skov, Adela Dumitrascu, Patric Simões Pereira, Katarina Abrahamsson, Silvia Bucci, Marina Duetsch, Andreas Stohl, Ivo Beck, Tiia Laurila, Byron Blomquist, Dean Howard, Stephen D. Archer, Ludovic Bariteau, Detlev Helmig, Jacques Hueber, Hans-Werner Jacobi, Kevin Posman, Lubna Dada, Kaspar R. Daellenbach and Alfonso Saiz-Lopez.

Nature Geoscience (2022),, 2022.


Unlike bromine, the effect of iodine chemistry on the Arctic surface ozone budget is poorly constrained. We present ship-based measurements of halogen oxides in the high Arctic boundary layer from the sunlit period of March to October 2020 and show that iodine enhances springtime tropospheric ozone depletion. We find that chemical reactions between iodine and ozone are the second highest contributor to ozone loss over the study period, after ozone photolysis-initiated loss and ahead of bromine.

The Chemistry of Mercury in the Stratosphere

Alfonso Saiz-Lopez, A. Ulises Acuña, Anoop S. Mahajan, Juan Z. Dávalos, Wuhu Feng, Daniel Roca-Sanjuán, Javier Carmona-García1, Carlos A. Cuevas, Douglas E. Kinnison, Juan Carlos Gómez Martín, Joseph S. Francisco and John M. C. Plane.

Geophysical Research Letters, 49, e2022GL097953., 2022.


Mercury, a global contaminant, enters the stratosphere through convective uplift, but its chemical cycling in the stratosphere is unknown. We report the first model of stratospheric mercury chemistry based on a novel photosensitized oxidation mechanism. We find two very distinct Hg chemical regimes in the stratosphere: in the upper stratosphere, above the ozone maximum concentration, Hg0 oxidation is initiated by photosensitized reactions, followed by second-step chlorine chemistry. In the lower stratosphere, ground-state Hg0 is oxidized by thermal reactions at much slower rates. This dichotomy arises due to the coincidence of the mercury absorption at 253.7 nm with the ozone Hartley band maximum at 254 nm. We also find that stratospheric Hg oxidation, controlled by chlorine and hydroxyl radicals, is much faster than previously assumed, but moderated by efficient photo-reduction of mercury compounds. Mercury lifetime shows a steep increase from hours in the upper-middle stratosphere to years in the lower stratosphere.

The influence of iodine on the Antarctic stratospheric ozone hole

Carlos A. Cuevas, Rafael P. Fernandez, Douglas E. Kinnison, Qinyi Li, Jean-François Lamarque, Tarek Trabelsi, Joseph S. Francisco, Susan Solomon, and Alfonso Saiz-Lopez.

PNAS 119 (7) e2110864119, , 2022.


The catalytic depletion of Antarctic stratospheric ozone is linked to anthropogenic emissions of chlorine and bromine. Despite its larger ozone-depleting efficiency, the contribution of ocean-emitted iodine to ozone hole chemistry has not been evaluated, due to the negligible iodine levels previously reported to reach the stratosphere. Based on the recently observed range (0.77 ± 0.1 parts per trillion by volume [pptv]) of stratospheric iodine injection, we use the Whole Atmosphere Community Climate Model to assess the role of iodine in the formation and recent past evolution of the Antarctic ozone hole. Our 1980–2015 simulations indicate that iodine can significantly impact the lower part of the Antarctic ozone hole, contributing, on average, 10% of the lower stratospheric ozone loss during spring (up to 4.2% of the total stratospheric column). We find that the inclusion of iodine advances the beginning and delays the closure stages of the ozone hole by 3 d to 5 d, increasing its area and mass deficit by 11% and 20%, respectively. Despite being present in much smaller amounts, and due to faster gas-phase photochemical reactivation, iodine can dominate (∼73%) the halogen-mediated lower stratospheric ozone loss during summer and early fall, when the heterogeneous reactivation of inorganic chlorine and bromine reservoirs is reduced. The stratospheric ozone destruction caused by 0.77 pptv of iodine over Antarctica is equivalent to that of 3.1 (4.6) pptv of biogenic very short-lived bromocarbons during spring (rest of sunlit period). The relative contribution of iodine to future stratospheric ozone loss is likely to increase as anthropogenic chlorine and bromine emissions decline following the Montreal Protocol.



The reaction between HgBr and O3: kinetic study and atmospheric implications

Juan Carlos Gómez Martín, Thomas R. Lewis, Kevin M. Douglas, Mark A. Blitz, Alfonso Saiz-Lopez and John M. C. Plane.

Phys. Chem. Chem. Phys.,


The rate constants of many reactions currently considered to be important in the atmospheric chemistry of mercury remain to be measured in the laboratory. Here we report the first experimental determination of the rate constant of the gas-phase reaction between the HgBr radical and ozone, for which a value at room temperature of k(HgBr + O3) = (7.5 ± 0.6) × 10−11 cm3 molecule s−1 (1σ) has been obtained. The rate constants of two reduction side reactions were concurrently determined: k(HgBr + O) = (5.3 ± 0.4) × 10−11 cm3 molecule s−1 and k(HgBrO + O) = (9.1 ± 0.6) × 10−11 cm3 molecule s−1. The value of k(HgBr + O3) is slightly lower than the collision number, confirming the absence of a significant energy barrier. Considering the abundance of ozone in the troposphere, our experimental rate constant supports recent modelling results suggesting that the main atmospheric fate of HgBr is reaction with ozone to form BrHgO.


Theoretical study of the NO3 radical reaction with CH2ClBr, CH2ICl, CH2BrI, CHCl2Br, and CHClBr2

Ibon Alkorta, John M. C. Plane, José Elguero,  Juan Z. DÁvalos, A. Ulises Acuña and Alfonso Saiz-Lopez

Phys. Chem. Chem. Phys., DOI: 10.1039/d2cp00021k, 2022.


The potential reaction of the nitrate radical (NO3), the main nighttime atmospheric oxidant, with five alkyl halides, halons (CH2ClBr, CH2ICl, CH2BrI, CHCl2Br, and CHClBr2) has been studied theoretically. The most favorable reaction corresponds to a hydrogen atom transfer. The stationary points on the potential energy surfaces of these reactions have been characterized. The reactions can be classified into two groups based on the number of hydrogen atoms in the halon molecules (1 or 2). The reactions with halons with only one hydrogen atom show more exothermic profiles than those with two hydrogen atoms. In addition, the kinetics of the reaction of NO3 + CH2BrI was studied in much higher detail using a multi-well Master Equation solver as a representative example of the nitrate radical reactivity against these halocarbons. These results indicate that the chemical lifetime of the alkyl halides would not be substantially affected by nitrate radical reactions, even in the case of NO3-polluted atmospheric conditions.

Graphical abstract: Theoretical study of the NO3 radical reaction with CH2ClBr, CH2ICl, CH2BrI, CHCl2Br, and CHClBr2

An unexpected large continental source of reactive bromine and chlorine with significant impact on wintertime air quality

Xiang Peng, Weihao Wang,  Men Xia, Hui Chen,  A.R. Ravishankara, Qinyi Li, Alfonso Saiz-Lopez, Pengfei Liu,  Fei Zhang, Chenglong Zhang, Likun Xue, Xinfeng Wang, Christian George, Jinhe Wang, Yujing Mu, Jianmin Chen and Tao Wang

National Science Review, nwaa304,, 2021


Halogen atoms affect the budget of ozone and the fate of pollutants such as hydrocarbons and mercury. Yet their sources and significances in polluted continental regions are poorly understood. Here we report the observation of unprecedented levels (averaging at 60 parts per trillion) of bromine chloride (BrCl) at a mid-latitude site in North China during winter. Widespread coal burning in rural households and a photo-assisted process were the primary source of BrCl and other bromine gases. BrCl contributed about 55% of both bromine and chlorine atoms. The halogen atoms increased the abundance of ‘conventional’ tropospheric oxidants (OH, HO2 and RO2) by 26%–73%, and enhanced oxidation of hydrocarbon by nearly a factor of two and the net ozone production by 55%. Our study reveals the significant role of reactive halogen in winter atmospheric chemistry and the deterioration of air quality in continental regions where uncontrolled coal combustion is prevalent.


Antarctic ozone hole modifies iodine geochemistry on the Antarctic Plateau

Andrea Spolaor, François Burgay, Rafael P. Fernandez, Clara Turetta, Carlos A. Cuevas, Kitae Kim, Douglas E. Kinnison, Jean-François Lamarque, Fabrizio de Blasi, Elena Barbaro, Juan Pablo Corella, Paul Vallelonga, Massimo Frezzotti, Carlo Barbante & Alfonso Saiz-Lopez

Nature Communication 12, 5836,, 2021.


Polar stratospheric ozone has decreased since the 1970s due to anthropogenic emissions of chlorofluorocarbons and halons, resulting in the formation of an ozone hole over Antarctica. The effects of the ozone hole and the associated increase in incoming UV radiation on terrestrial and marine ecosystems are well established; however, the impact on geochemical cycles of ice photoactive elements, such as iodine, remains mostly unexplored. Here, we present the first iodine record from the inner Antarctic Plateau (Dome C) that covers approximately the last 212 years (1800-2012 CE). Our results show that the iodine concentration in ice remained constant during the pre-ozone hole period (1800-1974 CE) but has declined twofold since the onset of the ozone hole era (~1975 CE), closely tracking the total ozone evolution over Antarctica. Based on ice core observations, laboratory measurements and chemistry-climate model simulations, we propose that the iodine decrease since ~1975 is caused by enhanced iodine re-emission from snowpack due to the ozone hole-driven increase in UV radiation reaching the Antarctic Plateau. These findings suggest the potential for ice core iodine records from the inner Antarctic Plateau to be as an archive for past stratospheric ozone trends.



Atmospheric formaldehyde, glyoxal and their relations to ozone pollution under low- and high-NOx regimes in summertime Shanghai, China

Yanlin Guo, Shanshan Wang, Jian Zhu, Ruifeng Zhang, Song Gao, Alfonso Saiz-Lopez , Bin Zhou

Atmospheric Research, Volume 258,, 2021


With the increasing concerns on summertime atmospheric photochemical pollution, the diagnosis and prevention of ozone pollution have been paid close attention. Both formaldehyde (HCHO) and glyoxal (CHOCHO) are ubiquitous oxidation intermediates of volatile organic compounds (VOCs). The ratio of glyoxal to formaldehyde (RGF) is used as a metric for VOCs emission sources. In this study, the mixing ratios of HCHO and CHOCHO have been measured by the active differential optical absorption spectroscopy (DOAS) method in the urban area of Shanghai during summertime in 2018, as well as other trace gases. The average levels of HCHO and CHOCHO are 3.31 ± 1.43 ppbv and 0.164 ± 0.073 ppbv, respectively. The similar diurnal patterns and high correlation between HCHO, CHOCHO and ozone levels implied that daytime photochemical processes are the dominant formation pathway for these trace gases. We find that with increased NOx levels, HCHO shows higher ozone formation potential relative to glyoxal. The RGF ratio increases with temperature and decreases with NO2 levels. By investigating the coupling of typical VOCs species such as acetylene, toluene and isoprene with HCHO and CHOCHO, RGF is found to be strongly impacted by the ambient VOCs profiles, suggesting that RGF should be used with caution when linking it to a given VOC precursor source. Finally, the RGF variations with ozone pollution episodes and weather processes are also discussed.

Chemical Interactions Between Ship-Originated Air Pollutants and Ocean-Emitted Halogens

Qinyi Li, Alba Badia, Rafael P. Fernandez, Anoop S. Mahajan, Ana Isabel López-Noreña, Yan Zhang, Shanshan Wang, Enrique Puliafito, Carlos A. Cuevas, and Alfonso Saiz-Lopez.

Journal of Geophysical Research: Atmospheres, 126, e2020JD034175., 2021.


Ocean‐going ships supply products from one region to another and contribute to the world’s economy. Ship exhaust contains many air pollutants and results in significant changes in marine atmospheric composition. The role of reactive halogen species (RHS) in the troposphere has received increasing recognition and oceans are the largest contributors to their atmospheric burden. However, the impact of shipping emissions on RHS and that of RHS on ship‐originated air pollutants have not been studied in detail. Here, an updated Weather Research Forecasting coupled with Chemistry model is utilized to explore the chemical interactions between ship emissions and oceanic RHS over the East Asia seas in summer. The emissions and resulting chemical transformations from shipping activities increase the level of NO and NO2 at the surface, increase O3 in the South China Sea, but decrease O3 in the East China Sea. Such changes in pollutants result in remarkable changes in the levels of RHS (>200% increase of chlorine; ∼30% and ∼5% decrease of bromine and iodine, respectively) as well as in their partitioning. The abundant RHS, in turn, reshape the loadings of air pollutants (∼20% decrease of NO and NO2; ∼15% decrease of O3) and those of the oxidants (>10% reduction of OH and HO2; ∼40% decrease of NO3) with marked patterns along the ship tracks. We, therefore, suggest that these important chemical interactions of ship‐originated emissions with RHS should be considered in the environmental policy assessments of the role of shipping emissions in air quality and climate.


Differing Mechanisms of New Particle Formation at Two Arctic Sites

Lisa J. Beck, Nina Sarnela, Heikki Junninen, Clara J. M. Hoppe, Olga Garmash, Federico Bianchi, Matthieu Riva, Clemence Rose, Otso Peräkylä, Daniela Wimmer, Oskari Kausiala, Tuija Jokinen, Lauri Ahonen, Jyri Mikkilä, Jani Hakala, Xu-Cheng He, Jenni Kontkanen, Klara K. E. Wolf, David Cappelletti, Mauro Mazzola, Rita Traversi, Chiara Petroselli, Angelo P. Viola, Vito Vitale, Robert Lange, Andreas Massling, Jakob K. Nøjgaard, Radovan Krejci, Linn Karlsson, Paul Zieger, Sehyun Jang, Kitack Lee, Ville Vakkari, Janne Lampilahti, Roseline C. Thakur, Katri Leino, Juha Kangasluoma, Ella-Maria Duplissy, Erkki Siivola, Marjan Marbouti, Yee Jun Tham, Alfonso Saiz-Lopez , Tuukka Petäjä, Mikael Ehn, Douglas R. Worsnop, Henrik Skov, Markku Kulmala, Veli-Matti Kerminen, and Mikko Sipilä.

Geophysical Research Letter, Volume 48, Issue 4,, 2021.


New particle formation in the Arctic atmosphere is an important source of aerosol particles. Understanding the processes of Arctic secondary aerosol formation is crucial due to their significant impact on cloud properties and therefore Arctic amplification. We observed the molecular formation of new particles from low‐volatility vapors at two Arctic sites with differing surroundings. In Svalbard, sulfuric acid (SA) and methane sulfonic acid (MSA) contribute to the formation of secondary aerosol and to some extent to cloud condensation nuclei (CCN). This occurs via ion‐induced nucleation of SA and NH3 and subsequent growth by mainly SA and MSA condensation during springtime and highly oxygenated organic molecules during summertime. By contrast, in an ice‐covered region around Villum, we observed new particle formation driven by iodic acid but its concentration was insufficient to grow nucleated particles to CCN sizes. Our results provide new insight about sources and precursors of Arctic secondary aerosol particles.


Direct field evidence of autocatalytic iodine release from atmospheric aerosol

Yee Jun Tham, Xu-Cheng Hea, Qinyi Li, Carlos A. Cuevas, Jiali Shen, Joni Kalliokoski, Chao Yan, Siddharth Iyer, Tuuli Lehmusjärvi, Sehyun Jang, Roseline C. Thakur, Lisa Beck, Deniz Kemppainen, Miska Olin, Nina Sarnela, Jyri Mikkilä, Jani Hakala, Marjan Marbouti, Lei Yao, Haiyan Li, Wei Huang, Yonghong Wang, Daniela Wimmer, Qiaozhi Zha, Juhani Virkanen, T. Gerard Spain, Simon O’Doherty, Tuija Jokinen, Federico Bianchi, Tuukka Petäjä, Douglas R. Worsnopa, Roy L. Mauldin III, Jurgita Ovadnevaite, Darius Ceburnis, Norbert M. Maier, Markku Kulmala, Colin O’Dowd, Miikka Dal Maso, Alfonso Saiz-Lopez, and Mikko Sipilä.

PNAS January 26, 2021 118 (4) e2009951118;, 2021


Reactive iodine plays a key role in determining the oxidation capacity, or cleansing capacity, of the atmosphere in addition to being implicated in the formation of new particles in the marine boundary layer. The postulation that heterogeneous cycling of reactive iodine on aerosols may significantly influence the lifetime of ozone in the troposphere not only remains poorly understood but also heretofore has never been observed or quantified in the field. Here, we report direct ambient observations of hypoiodous acid (HOI) and heterogeneous recycling of interhalogen product species (i.e., iodine monochloride [ICl] and iodine monobromide [IBr]) in a midlatitude coastal environment. Significant levels of ICl and IBr with mean daily maxima of 4.3 and 3.0 parts per trillion by volume (1-min average), respectively, have been observed throughout the campaign. We show that the heterogeneous reaction of HOI on marine aerosol and subsequent production of iodine interhalogens are much faster than previously thought. These results indicate that the fast formation of iodine interhalogens, together with their rapid photolysis, results in more efficient recycling of atomic iodine than currently considered in models. Photolysis of the observed ICl and IBr leads to a 32% increase in the daytime average of atomic iodine production rate, thereby enhancing the average daytime iodine-catalyzed ozone loss rate by 10 to 20%. Our findings provide direct field evidence that the autocatalytic mechanism of iodine release from marine aerosol is important in the atmosphere and can have significant impacts on atmospheric oxidation capacity.

Effect of bromine and iodine chemistry on tropospheric ozone over Asia-Pacific using the CMAQ model

Yeqi Huang, Xingcheng Lu, Jimmy C.H. Fung, Golam Sarwar, Zhenning Li, Qinyi Li, Alfonso Saiz-Lopez, Alexis K.H. Lau

Chemosphere 262 (2021) 127595


Recent studies have focused on the chemistry of tropospheric halogen species which are able to deplete tropospheric ozone (O3). In this study, the effect of bromine and iodine chemistry on tropospheric O3 within the annual cycle in Asia-Pacific is investigated using the CMAQ model with the newly embedded bromine and iodine chemistry and a blended and customized emission inventory considering marine halogen emission. Results indicate that the vertical profiles of bromine and iodine species show distinct features over land/ocean and daytime/nighttime, related to natural and anthropogenic emission distributions and photochemical reactions. The halogen-mediated O3 loss has a strong seasonal cycle, and reaches a maximum of −15.9 ppbv (−44.3%) over the ocean and −13.4 ppbv (−38.9%) over continental Asia among the four seasons. Changes in solar radiation, dominant wind direction, and nearshore chlorophyll-a accumulation all contribute to these seasonal differences. Based on the distances to the nearest coastline, the onshore and offshore features of tropospheric O3 loss caused by bromine and iodine chemistry are studied. Across a coastline-centric 400-km-wide belt from onshore to offshore, averaged maximum gradient of O3 loss reaches 1.1 ppbv/100 km at surface level, while planetary boundary layer (PBL) column mean of O3 loss is more moderate, being approximately 0.7 ppbv/100 km. Relative high halogen can be found over Tibetan Plateau (TP) and the largest O3 loss (approximately 4–5 ppbv) in the PBL can be found between the western boundary of the domain and the TP. Halogens originating from marine sources can potentially affect O3 concentration transported from the stratosphere over the TP region. As part of efforts to improve our understanding of the effect of bromine and iodine chemistry on tropospheric O3, we call for more models and monitoring studies on halogen chemistry and be considered further in air pollution prevention and control policy.

First-year sea ice leads to an increase in dimethyl sulfide-induced particle formation in the Antarctic Peninsula

Eunho Jang, Ki-Tae Parka, Young Jun Yoon, Kitae Kim, Yeontae Gim, Hyun Young Chung, Kitack Lee, Jinhee Choi, Jiyeon Park, Sang-Jong Park, Ja-Ho Koo, Rafael P. Fernandez, Alfonso Saiz-Lopez

Science of The Total Environment, Volume 803,, 2021


Dimethyl sulfide (DMS) produced by marine algae represents the largest natural emission of sulfur to the atmosphere. The oxidation of DMS is a key process affecting new particle formation that contributes to the radiative forcing of the Earth. In this study, atmospheric DMS and its major oxidation products (methanesulfonic acid, MSA; non-sea-salt sulfate, nss-SO42–) and particle size distributions were measured at King Sejong station located in the Antarctic Peninsula during the austral spring–summer period in 2018–2020. The observatory was surrounded by open ocean and first-year and multi-year sea ice. Importantly, oceanic emissions and atmospheric oxidation of DMS showed distinct differences depending on source regions. A high mixing ratio of atmospheric DMS was observed when air masses were influenced by the open ocean and first-year sea ice due to the abundance of DMS producers such as pelagic phaeocystis and ice algae. However, the concentrations of MSA and nss-SO42– were distinctively increased for air masses originating from first-year sea ice as compared to those originating from the open ocean and multi-year sea ice, suggesting additional influences from the source regions of atmospheric oxidants. Heterogeneous chemical processes that actively occur over first-year sea ice tend to accelerate the release of bromine monoxide (BrO), which is the most efficient DMS oxidant in Antarctica. Model-estimates for surface BrO confirmed that high BrO mixing ratios were closely associated with first-year sea ice, thus enhancing DMS oxidation. Consequently, the concentration of newly formed particles originated from first-year sea ice, which was a strong source area for both DMS and BrO was greater than from open ocean (high DMS but low BrO). These results indicate that first-year sea ice plays an important yet overlooked role in DMS-induced new particle formation in polar environments, where warming-induced sea ice changes are pronounced.

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Halogens Enhance Haze Pollution in China

Qinyi Li, Xiao Fu, Xiang Peng, Weihao Wang, Alba Badia, Rafael P. Fernandez, Carlos A. Cuevas, Yujing Mu, Jianmin Chen, Jose L. Jimenez, Tao Wang and Alfonso Saiz-Lopez

Environ. Sci. Technol.,, 2021.


Severe and persistent haze events in northern China, characterized by high loading of fine aerosol especially of secondary origin, negatively impact human health and the welfare of ecosystems. However, current knowledge cannot fully explain the formation of this haze pollution. Despite field observations of elevated levels of reactive halogen species (e.g., BrCl, ClNO2, Cl2, HBr) at several sites in China, the influence of halogens (particularly bromine) on haze pollution is largely unknown. Here, for the first time, we compile an emission inventory of anthropogenic bromine and quantify the collective impact of halogens on haze pollution in northern China. We utilize a regional model (WRF-Chem), revised to incorporate updated halogen chemistry and anthropogenic chlorine and bromine emissions and validated by measurements of atmospheric pollutants and halogens, to show that halogens enhance the loading of fine aerosol in northern China (on average by 21%) and especially its secondary components (∼130% for secondary organic aerosol and ∼20% for sulfate, nitrate, and ammonium aerosols). Such a significant increase is attributed to the enhancement of atmospheric oxidants (OH, HO2, O3, NO3, Cl, and Br) by halogen chemistry, with a significant contribution from previously unconsidered bromine. These results show that higher recognition of the impact of anthropogenic halogens shall be given in haze pollution research and air quality regulation.


Impact of dimethylsulfide chemistry on air quality over the Northern Hemisphere

Junri Zhao, Golam Sarwar, Brett Gantt, Kristen Foley, Barron H. Henderson, Havala O. T. Pye, Kathleen M. Fahey, Daiwen Kang, Rohit Mathur, Yan Zhang, Qinyi Li, Alfonso Saiz-Lopez

Atmospheric Environment, Volume 244,117961,, 2021


We implement oceanic dimethylsulfide (DMS) emissions and its atmospheric chemical reactions into the Community Multiscale Air Quality (CMAQv53) model and perform annual simulations without and with DMS chemistry to quantify its impact on tropospheric composition and air quality over the Northern Hemisphere. DMS chemistry enhances both sulfur dioxide (SO2) and sulfate (SO42−) over seawater and coastal areas. It enhances annual mean surface SO2 concentration by +46 pptv and SO42−by +0.33 μg/m3 and decreases aerosol nitrate concentration by −0.07 μg/m3 over seawater compared to the simulation without DMS chemistry. The changes decrease with altitude and are limited to the lower atmosphere. Impacts of DMS chemistry on SO42− are largest in the summer and lowest in the fall due to the seasonality of DMS emissions, atmospheric photochemistry and resultant oxidant levels. Hydroxyl and nitrate radical-initiated pathways oxidize 75% of the DMS while halogen-initiated pathways oxidize 25%. DMS chemistry leads to more acidic particles over seawater by decreasing aerosol pH. Increased SO42−from DMS enhances atmospheric extinction while lower aerosol nitrate reduces the extinction so that the net effect of DMS chemistry on visibility tends to remain unchanged over most of the seawater.

Improved Mechanistic Model of the Atmospheric Redox Chemistry of Mercury

Viral Shah, Daniel J. Jacob, Colin P. Thackray, Xuan Wang, Elsie M. Sunderland, Theodore S. Dibble, Alfonso Saiz-Lopez, Ivan Černušák, Vladimir Kellö, Pedro J. Castro, Rongrong Wu, and Chuji Wang

Environ. Sci. Technol. 2021,,2021


We present a new chemical mechanism for Hg0/HgI/HgII atmospheric cycling, including recent laboratory and computational data, and implement it in the GEOS-Chem global atmospheric chemistry model for comparison to observations. Our mechanism includes the oxidation of Hg0 by Br and OH, subsequent oxidation of HgI by ozone and radicals, respeciation of HgII in aerosols and cloud droplets, and speciated HgII photolysis in the gas and aqueous phases. The tropospheric Hg lifetime against deposition in the model is 5.5 months, consistent with observational constraints. The model reproduces the observed global surface Hg0 concentrations and HgII wet deposition fluxes. Br and OH make comparable contributions to global net oxidation of Hg0 to HgII. Ozone is the principal HgI oxidant, enabling the efficient oxidation of Hg0 to HgII by OH. BrHgIIOH and HgII(OH)2, the initial HgII products of Hg0 oxidation, respeciate in aerosols and clouds to organic and inorganic complexes, and volatilize to photostable forms. Reduction of HgII to Hg0 takes place largely through photolysis of aqueous HgII–organic complexes. 71% of model HgII deposition is to the oceans. Major uncertainties for atmospheric Hg chemistry modeling include Br concentrations, stability and reactions of HgI, and speciation and photoreduction of HgII in aerosols and clouds.

Improving the Characterization of Natural Emissions in CMAQ

Daiwen Kang, Jeff Willison, Golam Sarwar, J. Mike Madden, Christian Hogrefe, Rohit Mathur, Brett Gantt and Alfonso Saiz-Lopez

The Magazine for Environmental Managers • A&WMA, 2021.


A summary of recent updates to the Community Multiscale Air Quality modeling system concerning the characterization of naturally produced emissions—including lightning and soil nitrogen oxides, biogenic volatile organic compounds, and oceanic halogen compounds—and their impacts on model-predicted surface ozone.



Intercomparison Between Surrogate, Explicit, and Full Treatments of VSL Bromine Chemistry Within the CAM-Chem Chemistry-Climate Model

Rafael P. Fernandez, Javier A. Barrera, Ana Isabel López-Noreña, Douglas E. Kinnison, Julie Nicely, Ross J. Salawitch, Pamela A. Wales, Beatriz M. Toselli, Simone Tilmes, Jean-François Lamarque, Carlos A. Cuevas, and Alfonso Saiz-Lopez.

Geophysical Research Letter, Volume 48, Issue 4,, 2021.


Many Chemistry‐Climate Models (CCMs) include a simplified treatment of brominated very short‐lived (VSLBr) species by assuming CH3Br as a surrogate for VSLBr. However, neglecting a comprehensive treatment of VSLBr in CCMs may yield an unrealistic representation of the associated impacts. Here, we use the Community Atmospheric Model with Chemistry (CAM‐Chem) CCM to quantify the tropospheric and stratospheric changes between various VSLBr chemical approaches with increasing degrees of complexity (i.e., surrogate, explicit, and full). Our CAM‐Chem results highlight the improved accuracy achieved by considering a detailed treatment of VSLBr photochemistry, including sea‐salt aerosol dehalogenation and heterogeneous recycling on ice‐crystals. Differences between the full and surrogate schemes maximize in the lowermost stratosphere and midlatitude free troposphere, resulting in a latitudinally dependent reduction of ∼1–7 DU in total ozone column and a ∼5%–15% decrease of the OH/HO2 ratio. We encourage all CCMs to include a complete chemical treatment of VSLBr in the troposphere and stratosphere.


Iodine chemistry in the chemistry–climate model SOCOL-AERv2-I

Arseniy Karagodin-Doyennel, Eugene Rozanov, Timofei Sukhodolov, Tatiana Egorova, Alfonso Saiz-Lopez, Carlos A. Cuevas, Rafael P. Fernandez, Tomás Sherwen, Rainer Volkamer, Theodore K. Koenig, Tanguy Giroud and Thomas Peter.

Geosci. Model Dev., 14, 6623–6645, 2021


In this paper, we present a new version of the chemistry–climate model SOCOL-AERv2 supplemented by an iodine chemistry module. We perform three 20-year ensemble experiments to assess the validity of the modeled iodine and to quantify the effects of iodine on ozone. The iodine distributions obtained with SOCOL-AERv2-I agree well with AMAX-DOAS observations and with CAM-chem model simulations. For the present-day atmosphere, the model suggests that the iodine-induced chemistry leads to a 3 %–4 % reduction in the ozone column, which is greatest at high latitudes. The model indicates the strongest influence of iodine in the lower stratosphere with 30 ppbv less ozone at low latitudes and up to 100 ppbv less at high latitudes. In the troposphere, the account of the iodine chemistry reduces the tropospheric ozone concentration by 5 %–10 % depending on geographical location. In the lower troposphere, 75 % of the modeled ozone reduction originates from inorganic sources of iodine, 25 % from organic sources of iodine. At 50 hPa, the results show that the impacts of iodine from both sources are comparable. Finally, we determine the sensitivity of ozone to iodine by applying a 2-fold increase in iodine emissions, as it might be representative for iodine by the end of this century. This reduces the ozone column globally by an additional 1.5 %–2.5 %. Our results demonstrate the sensitivity of atmospheric ozone to iodine chemistry for present and future conditions, but uncertainties remain high due to the paucity of observational data of iodine species.



Modelling the impacts of iodine chemistry on thenorthern Indian Ocean marine boundary layer

Anoop S. Mahajan, Qinyi Li, Swaleha Inamdar, Kirpa Ram, Alba Badia and Alfonso Saiz-Lopez

Atmos. Chem. Phys., 21, 8437–8454, 2021


Recent observations have shown the ubiquitous presence of iodine oxide (IO) in the Indian Ocean marine boundary layer (MBL). In this study, we use the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem version 3.7.1), including halogen (Br, Cl, and I) sources and chemistry, to quantify the impacts of the observed levels of iodine on the chemical composition of the MBL. The model results show that emissions of inorganic iodine species resulting from the deposition of ozone (O3) on the sea surface are needed to reproduce the observed levels of IO, although the current parameterizations overestimate the atmospheric concentrations. After reducing the inorganic emissions by 40 %, a reasonable match with cruise-based observations is found, with the model predicting values between 0.1 and 1.2 pptv across the model domain MBL. A strong seasonal variation is also observed, with lower iodine concentrations predicted during the monsoon period, when clean oceanic air advects towards the Indian subcontinent, and higher iodine concentrations predicted during the winter period, when polluted air from the Indian subcontinent increases the ozone concentrations in the remote MBL. The results show that significant changes are caused by the inclusion of iodine chemistry, with iodine-catalysed reactions leading to regional changes of up to 25 % in O3, 50 % in nitrogen oxides (NO and NO2), 15 % in hydroxyl radicals (OH), 25 % in hydroperoxyl radicals (HO2), and up to a 50 % change in the nitrate radical (NO3), with lower mean values across the domain. Most of the large relative changes are observed in the open-ocean MBL, although iodine chemistry also affects the chemical composition in the coastal environment and over the Indian subcontinent. These results show the importance of including iodine chemistry in modelling the atmosphere in this region.

Observations of iodine monoxide over three summers at the Indian Antarctic bases of Bharati and Maitri

Anoop S. Mahajan, Mriganka S. Biswas, Steffen Beirle, Thomas Wagner, Anja Schönhardt, Nuria Benavent and Alfonso Saiz-Lopez

Atmos. Chem. Phys., 21, 11829–11842, 2021,


Iodine plays a vital role in oxidation chemistry over Antarctica, with past observations showing highly elevated levels of iodine oxide (IO) leading to severe depletion of boundary layer ozone in West Antarctica. Here, we present MAX-DOAS-based (multi-axis differential absorption spectroscopy) observations of IO over three summers (2015–2017) at the Indian Antarctic bases of Bharati and Maitri. IO was observed during all the campaigns with mixing ratios below 2 pptv (parts per trillion by volume) for the three summers, which are lower than the peak levels observed in West Antarctica. This suggests that sources in West Antarctica are different or stronger than sources of iodine compounds in East Antarctica, the nature of which is still uncertain. Vertical profiles estimated using a profile retrieval algorithm showed decreasing gradients with a peak in the lower boundary layer. The ground-based instrument retrieved vertical column densities (VCDs) were approximately a factor of 3 to 5 higher than the VCDs reported using satellite-based instruments, which is most likely related to the sensitivities of the measurement techniques. Air mass back-trajectory analysis failed to highlight a source region, with most of the air masses coming from coastal or continental regions. This study highlights the variation in iodine chemistry in different regions in Antarctica and the importance of a long-term dataset to validate models estimating the impacts of iodine chemistry.

Ozone depletion due to dust release of iodine in the free troposphere

Theodore K. Koenig, Rainer Volkamer, Eric C. Apel, James F. Bresch, Carlos A. Cuevas, Barbara Dix, Edwin W. Eloranta, Rafael P. Fernandez, Samuel R. Hall, Rebecca S. Hornbrook, R. Bradley Pierce, J. Michael Reeves, Alfonso Saiz-Lopez, Kirk Ullmann

Science Advances, Vol 7, Issue 52 • DOI: 10.1126/sciadv.abj6544, 2021.


Iodine is an atmospheric trace element emitted from oceans that efficiently destroys ozone (O3). Low O3 in airborne dust layers is frequently observed but poorly understood. We show that dust is a source of gas-phase iodine, indicated by aircraft observations of iodine monoxide (IO) radicals inside lofted dust layers from the Atacama and Sechura Deserts that are up to a factor of 10 enhanced over background. Gas-phase iodine photochemistry, commensurate with observed IO, is needed to explain the low O3 inside these dust layers (below 15 ppbv; up to 75% depleted). The added dust iodine can explain decreases in O3 of 8% regionally and affects surface air quality. Our data suggest that iodate reduction to form volatile iodine species is a missing process in the geochemical iodine cycle and presents an unrecognized aeolian source of iodine. Atmospheric iodine has tripled since 1950 and affects ozone layer recovery and particle formation.



Photochemistry and Non-adiabatic Photodynamics of the HOSO Radical

Javier Carmona-García,  Antonio Francés-Monerris, Carlos A. Cuevas, Tarek Trabelsi, Alfonso Saiz-Lopez, Joseph S. Francisco and Daniel Roca-Sanjuán

J. Am. Chem. Soc.,,2021


Hydroxysulfinyl radical (HOSO) is important due to its involvement in climate geoengineering upon SO2 injection and generation of the highly hygroscopic H2SO4. Its photochemical behavior in the upper atmosphere is, however, uncertain. Here we present the ultraviolet−visible photochemistry and photodynamics of this species by simulating the atmospheric conditions with high-level quantum chemistry methods. Photocleavage to HO + SO arises as the major solar-induced channel, with a minor contribution of H + SO2 photoproducts. The efficient generation of SO is relevant due to its reactivity with O3 and the consequent depletion of ozone in the stratosphere.

Photochemistry of HOSO2 and SO3 and Implications for the Production of Sulfuric Acid

Javier Carmona-García, Tarek Trabelsi, Antonio Francés-Monerris, Carlos A. Cuevas, Alfonso Saiz-Lopez, Daniel Roca-Sanjuán and Joseph S. Francisco.

J. Am. Chem. Soc.,, 2021.


Sulfur trioxide (SO3) and the hydroxysulfonyl radical (HOSO2) are two key intermediates in the production of sulfuric acid (H2SO4) on Earth’s atmosphere, one of the major components of acid rain. Here, the photochemical properties of these species are determined by means of high-level quantum chemical methodologies, and the potential impact of their light-induced reactivity is assessed within the context of the conventional acid rain generation mechanism. Results reveal that the photodissociation of HOSO2 occurs primarily in the stratospher through the ejection of hydroxyl radicals (•OH) and sulfur dioxide (SO2). This may decrease the production rate of H2SO4 in atmospheric regions with low O2 concentration. In contrast, the photostability of SO3 under stratospheric conditions suggests that its removal efficiency, still poorly understood, is key to assess the H2SO4 formation in the upper atmosphere.



Recent and historical pollution legacy in high altitude Lake Marboré (Central Pyrenees): A record of mining and smelting since pre-Roman times in the Iberian Peninsula

J.P. Corella, M.J. Sierra, A. Garralón, R.Millán, J. Rodríguez-Alonso, M.P.Mata, A. Vicente de Vera, A. Moreno, P. González-Sampériz, B. Duval, D. Amouroux, P. Vivez, C.A. Cuevas, J.A. Adame, B.Wilhelm, A. Saiz-Lopez, B.L. Valero-Garcés.

Science of The Total Environment, Volume 751, 10 January 2021, 141557,, 2021


We have analyzed potential harmful trace elements (PHTE; Pb, Hg, Zn, As and Cu) on sediment cores retrieved from lake Marboré (LM) (2612 m a.s.l, 42°41′N; 0° 2′E). PHTE variability allowed us to reconstruct the timing and magnitude of trace metal pollutants fluxes over the last 3000 years in the Central Pyrenees. A statistical treatment of the dataset (PCA) enabled us to discern the depositional processes of PHTE, that reach the lake via direct atmospheric deposition. Indeed, the location of LM above the atmospheric boundary layer makes this lake an exceptional site to record the long-range transport of atmospheric pollutants in the free troposphere. Air masses back-trajectories analyses enabled us to understand the transport pathways of atmospheric pollutants while lead isotopic analyses contributed to evaluate the source areas of metal pollution in SW Europe during the Late Holocene. PHTE variability, shows a clear agreement with the main exploitation phases of metal resources in Southern Europe during the Pre-Industrial Period. We observed an abrupt lead enrichment from 20 to 375 yrs CE mostly associated to silver and lead mining and smelting practices in Southern Iberia during the Roman Empire. This geochemical data suggests that regional atmospheric metal pollution during the Roman times rivalled the Industrial Period. PHTE also increased during the High and Late Middle Ages (10–15th centuries) associated to a reactivation of mining and metallurgy activities in high altitude Pyrenean mining sites during climate amelioration phases. Atmospheric mercury deposition in the Lake Marboré record mostly reflects global emissions, particularly from Almadén mines (central Spain) and slightly fluctuates during the last three millennia with a significant increase during the last five centuries. Our findings reveal a strong mining-related pollution legacy in alpine lakes and watersheds that needs to be considered in management plans for mountain ecosystems as global warming and human pressure effects may contribute to their future degradation.


Role of iodine oxoacids in atmospheric aerosol nucleation

Xu-Cheng He, Yee Jun Tham, Lubna Dada, Mingyi Wang, Henning Finkenzeller, Dominik Stolzenburg, Siddharth Iyer, Mario Simon, Andreas Kürten, Jiali Shen, Birte Rörup, Matti Rissanen, Siegfried Schobesberger, Rima Baalbaki, Dongyu S. Wang, Theodore K. Koenig, Tuija Jokinen, Nina Sarnela, Lisa J. Beck, João Almeida, Stavros Amanatidis, António Amorim, Farnoush Ataei, Andrea Baccarini, Barbara Bertozzi, Federico Bianchi, Sophia Brilke, Lucía Caudillo, Dexian Chen, Randall Chiu, Biwu Chu, António Dias, Aijun Ding, Josef Dommen, Jonathan Duplissy, Imad El Haddad, Loïc Gonzalez Carracedo, Manuel Granzin, Armin Hansel, Martin Heinritzi, Victoria Hofbauer, Heikki Junninen, Juha Kangasluoma, Deniz Kemppainen, Changhyuk Kim, Weimeng Kong, Jordan E. Krechmer, Aleksander Kvashin, Totti Laitinen, Houssni Lamkaddam, Chuan Ping Lee, Katrianne Lehtipalo, Markus Leiminger, Zijun Li, Vladimir Makhmutov, Hanna E. Manninen, Guillaume Marie, Ruby Marten, Serge Mathot, Roy L. Mauldin, Bernhard Mentler, Ottmar Möhler, Tatjana Müller, Wei Nie, Antti Onnela, Tuukka Petäjä, Joschka Pfeifer, Maxim Philippov, Ananth Ranjithkumar, Alfonso Saiz-Lopez, Imre Salma, Wiebke Scholz, Simone Schuchmann, Benjamin Schulze, Gerhard Steiner, Yuri Stozhkov, Christian Tauber, António Tomé, Roseline C. Thakur, Olli Väisänen, Miguel Vazquez-Pufleau, Andrea C. Wagner, Yonghong Wang, Stefan K. Weber, Paul M. Winkler, Yusheng Wu, Mao Xiao, Chao Yan, Qing Ye, Arttu Ylisirniö, Marcel Zauner-Wieczorek, Qiaozhi Zha, Putian Zhou, Richard C. Flagan, Joachim Curtius, Urs Baltensperger, Markku Kulmala, Veli-Matti Kerminen, Theo Kurtén, Neil M. Donahue, Rainer Volkamer, Jasper Kirkby, Douglas R. Worsnop, Mikko Sipilä.

Science 05 Feb 2021: Vol. 371, Issue 6529, pp. 589-595 DOI: 10.1126/science.abe0298, 2021.


Iodic acid (HIO3) is known to form aerosol particles in coastal marine regions, but predicted nucleation and growth rates are lacking. Using the CERN CLOUD (Cosmics Leaving Outdoor Droplets) chamber, we find that the nucleation rates of HIO3 particles are rapid, even exceeding sulfuric acid–ammonia rates under similar conditions. We also find that ion-induced nucleation involves IO3− and the sequential addition of HIO3 and that it proceeds at the kinetic limit below +10°C. In contrast, neutral nucleation involves the repeated sequential addition of iodous acid (HIO2) followed by HIO3, showing that HIO2 plays a key stabilizing role. Freshly formed particles are composed almost entirely of HIO3, which drives rapid particle growth at the kinetic limit. Our measurements indicate that iodine oxoacid particle formation can compete with sulfuric acid in pristine regions of the atmosphere.

Sea ice in the northern North Atlantic through the Holocene: Evidence from ice cores and marine sediment records

Niccolò Maffezzoli, Bjørg Risebrobakken, Martin W. Miles, Paul Vallelong, Sarah M.P. Berben, Federico Scoto, RossEdwards, Helle Astrid Kjær, Henrik Sadatzki, Alfonso Saiz-Lopez, Clara Turetta, Carlo Barbante, Bo Vinther, Andrea Spolaor.

Quaternary Science Reviews, Volume 273, 107249,, 2021.


Sea ice plays a pivotal role in Earth's climate and its past reconstruction is crucial to investigate the connections and feedbacks with the other components of the climate system. Among the available archives that store information of past sea ice are marine and ice cores. Recent studies on the IP25 biomarker extracted from marine sediments has shown great skill to infer past changes of Arctic sea ice. In ice matrixes, sodium, bromine and iodine have shown potential to store the fingerprint of sea ice presence. The development of an unambiguous sea ice proxy from ice cores, however, has proven to be a challenging task especially in the Arctic realm.

In this work we analyze the sodium, bromine and iodine records in the RECAP ice core, coastal eastern Greenland, to investigate the sea ice variability in the northern North Atlantic Ocean through the last 11,000 years of the current interglacial, i.e. the Holocene. We compare the RECAP records with marine sea ice proxy records available from the northern North Atlantic.

We suggest that RECAP sodium concentrations can be associated with variability of sea ice extent, while the bromine-to-sodium ratios and iodine are associated respectively with seasonal sea ice and bioproductivity from open ocean and fresh sea ice surfaces.

According to our interpretation, we find that sea ice was at its lowest extent and seasonal in nature during the early Holocene in all regions of the North Atlantic. Increasing sea ice signals are seen from ca. 8–9 ka b2k, in line with long-term Holocene cooling. The increasing sea ice trend appears uninterrupted in the Fram Strait and North Iceland while reaching a maximum ca. 5 ka b2k in the East Greenland region. Sea ice modifications during the last 5000 years display great variability in East Greenland with intermediate conditions between the early and mid Holocene, possibly associated with local fjord dynamics. The last sea ice maximum was reached across all regions 1000 years b2k.



Sea-ice reconstructions from bromine and iodine in ice cores

Paul Vallelonga , Niccolo Maffezzoli, Alfonso Saiz-Lopez, Federico Scoto, Helle Astrid Kjær, Andrea Spolaor

Quaternary Science Reviews, Volume 269, 1 October 2021, 107133,, 2021


As the intricacies of paleoclimate dynamics are explored, it is becoming understood that sea-ice variability can instigate, or contribute to, climate change instabilities commonly described as “tipping points”. Compared to ice sheets and circulating ocean currents, sea-ice is ephemeral and continental-scale changes to sea ice cover occur seasonally. Sea-ice greatly influences polar albedo, atmosphere-ocean gas exchange and vertical mixing of polar ocean masses. Major changes in sea ice distribution and thickness have been invoked as drivers of deglaciations as well as stadial climate variability described in Greenland climate records as “Dansgaard-Oeschger” cycles and described in Antarctic climate records as “Antarctic Isotopic Maxima”.

The role of halogens in polar atmospheric chemistry has been studied intensively over the past few decades. This research has been driven by the role of bromine, primarily as gas-phase bromine monoxide (BrO), which exerts a key control on polar tropospheric ozone concentrations. Initial findings led to the discovery of boundary-layer self-catalyzing heterogeneous bromine reactions fed by sunlight and ozone, known as bromine explosions. First-year sea-ice and blowing snow have been identified as key components for this heterogeneous bromine recycling in the polar boundary layer. This understanding of polar halogen chemistry – supported by an expanding body of observations and modeling – has formed the basis for investigating quantitative links between halogen concentrations in the polar atmospheric boundary layer and sea-ice presence and/or extent.

Despite the clear importance of sea-ice in paleoclimate research, the ice core community lacks a conservative and quantitative proxy for sea-ice extent. The most commonly applied proxy, methanesulphonic acid (MSA), is volatile and has not been demonstrated reliably for ice core records extending beyond the last few centuries. Sodium has also been applied to reconstruct sea-ice extent in a semi-quantitative manner although the effects of meteorological transport noise are significant. Contrary to a priori expectations, the halogens bromine and iodine appear to be stable in polar snow and ice over millennial timescales, addressing the temporal limitations of MSA records. Unfortunately, transport and meteorological variability influence sodium deposition as well as the deposition of halogens and the many other ionic impurities found in ice cores. The atmospheric chemistry of halogens is more complex than those of sodium or MSA due to the mixed-phase (gas and aerosol) nature of halogen photochemistry. Thus the application of halogen records in ice cores to sea-ice reconstruction overcomes some challenges posed by existing proxies, but also opens new challenges specific to halogens. Challenges common to all sea-ice proxies include the deconvolution of changes in emission source locations and changes in transport efficacy, particularly those occurring during climate transitions combining changes in sea-ice and atmospheric circulation, such as stadial/interstadial or glacial/interglacial climate variability.

In this review, we describe the rationale and available evidence for linking the halogens bromine and iodine found in polar snow and ice to sea-ice extent. Reported measurements of bromine and iodine in polar snow and ice samples are critically discussed. We also consider aspects of halogen transport and retention in polar snow and ice that are still poorly understood. Overall, there is a growing body of evidence supporting the application of bromine to sea-ice reconstructions, and the use of iodine to reconstruct marine biological activity mediated in part by sea-ice extent. These halogens complement existing sea-ice proxies but most crucially, offer the capacity to greatly extend the temporal and spatial coverage of ice core-based sea-ice reconstructions. We identify knowledge gaps existing in the current understanding of spatial and temporal variability of halogen distributions in the polar regions. We suggest areas where polar halogen chemistry can contribute to a better understanding of the halogen records recovered from ice cores. Finally, we propose future steps for establishing reliable and constructive sea-ice reconstructions based on bromine and iodine as observed in snow and ice cores.

Spatial and Temporal Variability of Iodine in Aerosol

Juan Carlos Gómez Martín, Alfonso Saiz-Lopez, Carlos A. Cuevas, Rafael P. Fernandez, Benjamin Gilfedder, Rolf Weller, Alex R. Baker, Elise Droste, and Senchao Lai

Journal of Geophysical Research: Atmospheres, 126, e2020JD034410., 2021


In this work, we describe the compilation and homogenization of an extensive data set of aerosol iodine field observations in the period between 1963 and 2018 and we discuss its spatial and temporal dependences by comparison with CAM‐Chem model simulations. A close to linear relationship between soluble and total iodine in aerosol is found (∼80% aerosol iodine is soluble), which enables converting a large subset of measurements of soluble iodine into total iodine. The resulting data set shows a distinct latitudinal dependence, with an enhancement toward the Northern Hemisphere (NH) tropics and lower values toward the poles. This behavior, which has been predicted by atmospheric models to depend on the global distribution of the main oceanic iodine source (which in turn depends on the reaction of ozone with aqueous iodide on the sea water‐air interface, generating gas‐phase I2 and HOI), is confirmed here by field observations for the first time. Longitudinally, there is some indication of a wave‐one profile in the tropics, which peaks in the Atlantic and shows a minimum in the Pacific. New data from Antarctica show that the south polar seasonal variation of iodine in aerosol mirrors that observed previously in the Arctic, with two equinoctial maxima and the dominant maximum occurring in spring. While no clear seasonal variability is observed in NH middle latitudes, there is an indication of different seasonal cycles in the NH tropical Atlantic and Pacific. Long‐term trends cannot be unambiguously established as a result of inhomogeneous time and spatial coverage and analytical methods.

The Mars Environmental Dynamics Analyzer, MEDA. A Suite of Environmental Sensors for the Mars 2020 Mission

J.A. Rodriguez-Manfredi, M. de la Torre Juárez, A. Alonso, V. Apéstigue, I. Arruego, T. Atienza, D. Banfield, J. Boland, M.A. Carrera, L. Castañer, J. Ceballos, H. Chen-Chen, A. Cobos, P.G. Conrad, E. Cordoba, T. del Río-Gaztelurrutia, A. de Vicente-Retortillo, M. Domínguez-Pumar, S. Espejo, A.G. Fairen, A. Fernández-Palma, R. Ferrándiz, F. Ferri, E. Fischer, A. García-Manchado, M. García-Villadangos, M. Genzer, S. Giménez, J. Gómez-Elvira,  F. Gómez, S.D. Guzewich, A.-M. Harri, C.D. Hernández, M. Hietam, R. Hueso, I. Jaakonaho, J.J. Jiménez, V. Jiménez, A. Larman, R. Leiter, A. Lepinette, M.T. Lemmon, G. López, S.N. Madsen, T. Mäkinen, M. Marín, J. Martín-Soler, G. Martínez,  A. Molina, L. Mora-Sotomayor, J.F. Moreno-Álvarez, S. Navarro, C.E. Newman, C. Ortega, M.C. Parrondo, V. Peinado, A. Peña, I. Pérez-Grande, S. Pérez-Hoyos, J. Pla-García, J. Polkko, M. Postigo, O. Prieto-Ballesteros, S.C.R. Rafkin, M. Ramos, M.I. Richardson, J. Romeral, C. Romero, K.D. Runyon. A. Saiz-Lopez, A. Sánchez-Lavega, I. Sard, J.T. Schofield, E. Sebastian,  M.D. Smith, R.J. Sullivan, L.K. Tamppari, A.D. Thompson, D. Toledo, F. Torrero,  J. Torres, R. Urquí, T. Velasco, D. Viúdez-Moreiras, S. Zurita, The MEDA team.

Space Science Reviews (2021) 217:48, 2021


NASA’s Mars 2020 (M2020) rover mission includes a suite of sensors to monitor current environmental conditions near the surface of Mars and to constrain bulk aerosol properties from changes in atmospheric radiation at the surface. The Mars Environmental Dynamics Analyzer (MEDA) consists of a set of meteorological sensors including wind sensor, a barometer, a relative humidity sensor, a set of 5 thermocouples to measure atmospheric temperature at ∼1.5 m and ∼0.5 m above the surface, a set of thermopiles to characterize the thermal IR brightness temperatures of the surface and the lower atmosphere. MEDA adds a radiation and dust sensor to monitor the optical atmospheric properties that can be used to infer bulk aerosol physical properties such as particle size distribution, non-sphericity, and concentration. The MEDA package and its scientific purpose are described in this document as well as how it responded to the calibration tests and how it helps prepare for the human exploration of Mars. A comparison is also presented to previous environmental monitoring payloads landed on Mars on the Viking, Pathfinder, Phoenix, MSL, and InSight spacecraft.

The Role of Natural Halogens in Global Tropospheric Ozone Chemistry and Budget Under Different 21st Century Climate Scenarios

Alba Badia, Fernando Iglesias-Suarez , Rafael P. Fernandez , Carlos A. Cuevas, Douglas E. Kinnison, Jean-Francois Lamarque, Paul T. Griffiths, David W. Tarasick, Jane Liu and Alfonso Saiz-Lopez.

JRG Atmospheres, Volume126, Issue20,, 2021.


Tropospheric ozEone ( O3 ) is an important greenhouse gas and a surface pollutant. The future evolutiEon of O3 abundances and chemical processing are uncertain due to a changing climate, socioeconomic developments, and missing chemistry in global models. Here, we use an Earth System Model with natural halogen chemistry to investigate the changes iEn the O3 budget over the 21st century following Representative Concentration Pathway (RCP)6.0 and RCP8.5 climate scenarios. Our results indicate that the global tropospEheric O3 net chemical change (NCC, chemical gross production minus destruction) will decrease 50% , notwithstanding increasing or decreasing trends in ozone production and loss. However, a wide range of surface NCC variations (fromE −60% Eto 150% ) are projected over polluted regions with stringent abatemeEnts in O3 precursor emissions. Water vapor and iodine are found to be key drivers of future tropospEheric O3 destruction, while the largest changEes in O3 production are determined by the future evolution of peroxy radicals. We show that natural halogens, currently not considered in climate models, significantly impact on the present-day and future gElobal O3 burden redEucing  30–35 Tg (E11–15% ) of tropospheric ozone throughout the 21st century regardless of the RCP scenario considered. This highlights the importance of including natural halogen chemistry in climate model projections of future tropospheric ozone.



Tropical Stratospheric Circulation and Ozone Coupled to Pacific Multi-Decadal Variability

Fernando Iglesias-Suarez, Oliver Wild, Douglas E. Kinnison, Rolando R. Garcia, Daniel R. Marsh, Jean-François Lamarque, Edmund M. Ryan, Sean M. Davis, Roland Eichinger, Alfonso Saiz-Lopez, and Paul J. Young

Geophysical Research Letters, Volume 48, Issue11,, 2021


Observational and modeling evidence suggest a recent acceleration of the stratospheric Brewer-Dobson circulation (BDC), driven by climate change and stratospheric ozone depletion. However, slowly varying natural variability can compromise our ability to detect such forced changes over the relatively short observational record. Using observations and chemistry-climate model simulations, we demonstrate a link between multi-decadal variability in the strength of the BDC and the Interdecadal Pacific Oscillation (IPO), with knock-on impacts for composition in the stratosphere. After accounting for the IPO-like variability in the BDC, the modeled trend is approximately 7%–10% dec−1 over 1979–2010. Furthermore, we find that sea surface temperatures explain up to 50% of the simulated decadal variability in tropical mid-stratospheric ozone. Our findings demonstrate strong links between low-frequency variability in the oceans, troposphere and stratosphere, as well as their potential importance in detecting structural changes in the BDC and future ozone recovery.

Two-dimensional monitoring of air pollution in Madrid usinga Multi-AXis Differential Optical Absorption Spectroscopytwo-dimensional (MAXDOAS-2D) instrument

David Garcia-Nieto, Nuria Benavent, Rafael Borge and Alfonso Saiz-Lopez

Atmos. Meas. Tech., 14, 2941–2955, 2021,


Trace gases play a key role in the chemistry of ur-ban atmospheres. Therefore, knowledge about their spatialdistribution is needed to fully characterize air quality in ur-ban areas. Using a new Multi-AXis Differential Optical Ab-sorption Spectroscopy two-dimensional (MAXDOAS-2D)instrument, along with an inversion algorithm (bePRO), wereport the first two-dimensional maps of nitrogen dioxide(NO2)and nitrous acid (HONO) concentrations in the city ofMadrid, Spain. Measurements were made during 2 months(6 May–5 July 2019), and peak mixing ratios of 12 and0.7 ppbv (parts per billion by volume) for NO2and HONO,respectively, were observed in the early morning in the south-ern part of the downtown area. We found good general agree-ment between the MAXDOAS-2D mesoscale observations– which provide a typical spatial range of a few kilometers– and the in situ measurements provided by Madrid’s airquality monitoring stations. In addition to vertical profiles,we studied the horizontal gradients of NO2in the surfacelayer by applying the different horizontal light path lengthsin the two spectral regions included in the NO2spectral anal-ysis: ultraviolet (UV, at 360 nm) and visible (VIS, 477 nm).We also investigate the sensitivity of the instrument to infervertically distributed information on aerosol extinction co-efficients and discuss possible future ways to improve theretrievals. The retrieval of two-dimensional distributions oftrace gas concentrations reported here provides valuable spa-tial information for the study of air quality in the city of Madrid.

A gas-to-particle conversion mechanism helps to explain atmospheric particle formation through clustering of iodine oxides

Juan Carlos Gómez Martín, Thomas R. Lewis, Mark A. Blitz, John M. C. Plane, Manoj Kumar, Joseph S. Francisco & Alfonso Saiz-Lopez

Nature Communications volume 11, Article number: 4521 (2020),


Emitted from the oceans, iodine-bearing molecules are ubiquitous in the atmosphere and a source of new atmospheric aerosol particles of potentially global significance. However, its inclusion in atmospheric models is hindered by a lack of understanding of the first steps of the photochemical gas-to-particle conversion mechanism. Our laboratory results show that under a high humidity and low HOx regime, the recently proposed nucleating molecule (iodic acid, HOIO2) does not form rapidly enough, and gas-to-particle conversion proceeds by clustering of iodine oxides (IxOy), albeit at slower rates than under dryer conditions. Moreover, we show experimentally that gas-phase HOIO2 is not necessary for the formation of HOIO2-containing particles. These insights help to explain new particle formation in the relatively dry polar regions and, more generally, provide for the first time a thermochemically feasible molecular mechanism from ocean iodine emissions to atmospheric particles that is currently missing in model calculations of aerosol radiative forcing.

Atmospheric formaldehyde at El Teide and Pic du Midi remote high-altitude sites

Cristina Prados-Roman, Miguel Fernández, Laura Gómez-Martín, Emilio Cuevas, Manuel Gil‑Ojeda, Nicolas Marusczak, Olga Puentedura, Jeroen E.Sonke and AlfonsoSaiz-Lopez

Atmospheric Environment 234 (2020) 117618


Formaldehyde (CH2O) is a tracer of the photochemical activity of the atmosphere. Linked to air quality, CH2O is an ozone (O3) precursor and serves as a proxy for natural and anthropogenic reactive organic emissions. As a product of the photooxidation of methane (CH4) and other hydrocarbons (e.g., isoprene), CH2O represents an important source of radicals in the remote free troposphere. This work aims at improving the characterization of this part of the troposphere where data are scarce. In particular, this study assesses the presence of CH2O at two high-altitude remote sites: El Teide (TEI, 3570 m a.s.l., Tenerife, Canary Islands, Spain) and Pic du Midi (PDM, 2877 m a.s.l., French Pyrenees). Through ground-based remote sensing measurements performed during two field campaigns in July (TEI) and September (PDM) 2013, this study presents the vertical distribution of CH2O at both locations. Results at PDM show that CH2O mixing ratios follow a decreasing vertical profile with a mean maximum of 0.5 ± 0.2 nmol mol−1 (i.e., ppbv) at the instruments' altitude. At TEI, observations indicate an uplifted layer of CH2O with a mean maximum of 1.3 ± 0.3 nmol mol−1 at 3.8 km a.s.l. (i.e., 300 m above the instrument's altitude). At both remote sites, the observed CH2O levels are higher than expected for background methane oxidation (a threefold increase in the case of TEI). Air mass back trajectory analysis links CH2O observations with abundant natural (e.g. forests) and/or anthropogenic isoprene emissions from the region nearby PDM, while the high CH2O levels detected at TEI indicate in-plume formation of CH2O resulting from its precursors emitted from west-African and Canadian fires. Finally, as a key trace gas for O3 and HOx chemistries, we estimate the upper limit of bromine monoxide (BrO) in the free troposphere at TEI and PDM to be 0.8 and 1.5 pmol mol−1 (i.e., pptv) respectively.

Determination of the absorption cross sections of higher-orderiodine oxides at 355 and 532 nm

Thomas R. Lewis, Juan Carlos Gómez Martín, Mark A. Blitz, Carlos A. Cuevas, John M. C. Plane, and Alfonso Saiz-Lopez

Atmos. Chem. Phys., 20, 10865–10887, 2020


Iodine oxides (IxOy) play an important role inthe atmospheric chemistry of iodine. They are initiatorsof new particle formation events in the coastal and polarboundary layers and act as iodine reservoirs in troposphericozone-depleting chemical cycles. Despite the importance ofthe aforementioned processes, the photochemistry of thesemolecules has not been studied in detail previously. Here,we report the first determination of the absorption crosssections of IxOy,x=2, 3, 5,y=1–12 atλ=355 nm bycombining pulsed laser photolysis of I2/O3gas mixturesin air with time-resolved photo-ionization time-of-flightmass spectrometry, using NO2actinometry for signalcalibration. The oxides selected for absorption cross-sectiondeterminations are those presenting the strongest signalsin the mass spectra, where signals containing four iodineatoms are absent. The method is validated by measuringthe absorption cross section of IO at 355 nm,σ355 nm,IO=(1.2±0.1)×10−18cm2, which is found to be in goodagreement with the most recent literature. The resultsobtainedareσ355 nm,I2O3<5×10−19cm2molec.−1,σ355 nm,I2O4=(3.9±1.2)×10−18cm2molec.−1,σ355 nm,I3O6=(6.1±1.6)×10−18cm2molec.−1,σ355 nm,I3O7=(5.3±1.4)×10−18cm2molec.−1,andσ355 nm,I5O12=(9.8±1.0)×10−18cm2molec.−1.Pho-todepletion atλ=532 nm was only observed for OIO,which enabled determination of upper limits for the ab-sorption cross sections of IxOyat 532 nm using OIO as anactinometer. These measurements are supplemented with abinitio calculations of electronic spectra in order to estimateatmospheric photolysis ratesJ(IxOy). Our results confirma highJ(IxOy) scenario where IxOyis efficiently removedduring daytime, implying enhanced iodine-driven ozonedepletion and hindering iodine particle formation. PossibleI2O3and I2O4photolysis products are discussed, includingIO3, which may be a precursor to iodic acid (HIO3) in thepresence of HO2.

Diurnal variation in Mars equatorial odd oxygen species: Chemical production and loss mechanisms

D. Viúdez-Moreiras, A. Saiz-Lopez, C.S. Blaszczak-Boxe, J.A. Rodriguez Manfredi and Y.L. Yung

Icarus 336 (2020) 113458


Odd oxygen (O, O(1D), O3) abundance and its variability in the Martian atmosphere results from complex physical and chemical interactions among atmospheric species, which are driven mainly by solar radiation and atmospheric conditions. Although our knowledge of Mars’ ozone distribution and variability has been significantly improved with the arrival of several recent orbiters, the data acquired by such missions is not enough to properly characterize its diurnal variation. Thus, photochemical models are useful tools to assist in such a characterization. Here, both the Martian ozone vertical distribution and its diurnal variation for equatorial latitudes are studied, using the JPL/Caltech one-dimensional photochemical model and diurnally-variable atmospheric profiles. The chosen equatorial latitude-region is based on the recent and future plans of NASA and other agencies to study this region by different surface missions. A production and loss analysis is performed in order to characterize the chemical mechanisms that drive odd oxygen's diurnal budget and variability on Mars making use of the comprehensive chemistry implemented in the model. The diurnal variation shows large differences in the abundance between daytime and nighttime; and variable behavior depending on the atmospheric layer. The photolysis-driven ozone diurnal profile is obtained at the surface, whilst a sharp decrease is obtained in the upper troposphere at daytime, which originates from the large differences in atomic oxygen abundances between atmospheric layers. Finally, no clear anticorrelation between ozone and water vapor is found in the diurnal cycle, contrary to the strong correlation observed by orbiters on a seasonal timescale.

Entangled iodine and hydrogen peroxide formation in ice

Yong Su Baek, Kitae Kim, Alfonso Saiz-Lopez, Dae Wi Min, Bomi Kim, Wonyong Choie and Cheol Ho Choi.

Phys. Chem. Chem. Phys., 2020, DOI: 10.1039/D0CP02966A (Communication), 2020.



Ice-core records show that anthropogenic pollution has increased the global atmospheric concentrations of hydrogen peroxide and iodine since the mid-20th century. Here, for the first time, we demonstrate a highly efficient mechanism that synergistically produces them in icy water conditions. This reaction is aided by a key intermediate IO2H, formed by an I ion with a dissolved O2 in acidic icy water, which produces both I as well as O2H radicals. I recombines with I to produce I2 at a diffusion-limited rate, followed by formation of I3 through disproportionation, while O2H yields H2O2 with I and a proton dissolved in icy water.

Estimation of reactive inorganic iodine fluxes in the Indian and Southern Ocean marine boundary layer

Swaleha Inamdar, Liselotte Tinel, Rosie Chance, Lucy J. Carpenter, Prabhakaran Sabu, Racheal Chacko, Sarat C. Tripathy, Anvita U. Kerkar, Alok K. Sinha, Parli Venkateswaran Bhaskar, Amit Sarkar, Rajdeep Roy, Tomás Sherwen, Carlos Cuevas, Alfonso Saiz-Lopez, Kirpa Ram, and Anoop S. Mahajan

Atmos. Chem. Phys., 20, 12093–12114, 2020,


Iodine chemistry has noteworthy impacts on the oxidising capacity of the marine boundary layer (MBL) through the depletion of ozone (O3) and changes to HOx (OH∕HO2) and NOx (NO∕NO2) ratios. Hitherto, studies have shown that the reaction of atmospheric O3 with surface seawater iodide (I−) contributes to the flux of iodine species into the MBL mainly as hypoiodous acid (HOI) and molecular iodine (I2). Here, we present the first concomitant observations of iodine oxide (IO), O3 in the gas phase, and sea surface iodide concentrations. The results from three field campaigns in the Indian Ocean and the Southern Ocean during 2015–2017 are used to compute reactive iodine fluxes in the MBL. Observations of atmospheric IO by multi-axis differential optical absorption spectroscopy (MAX-DOAS) show active iodine chemistry in this environment, with IO values up to 1 pptv (parts per trillion by volume) below latitudes of 40∘ S. In order to compute the sea-to-air iodine flux supporting this chemistry, we compare previously established global sea surface iodide parameterisations with new region-specific parameterisations based on the new iodide observations. This study shows that regional changes in salinity and sea surface temperature play a role in surface seawater iodide estimation. Sea–air fluxes of HOI and I2, calculated from the atmospheric ozone and seawater iodide concentrations (observed and predicted), failed to adequately explain the detected IO in this region. This discrepancy highlights the need to measure direct fluxes of inorganic and organic iodine species in the marine environment. Amongst other potential drivers of reactive iodine chemistry investigated, chlorophyll a showed a significant correlation with atmospheric IO (R=0.7 above the 99 % significance level) to the north of the polar front. This correlation might be indicative of a biogenic control on iodine sources in this region.

Frequent new particle formation over the high Arctic pack ice by enhanced iodine emissions

Andrea Baccarini, Linn Karlsson, Josef Dommen, Patrick Duplessis, Jutta Vüllers, Ian M. Brooks, Alfonso Saiz-Lopez, Matthew Salter, Michael Tjernström, Urs Baltensperger, Paul Zieger & Julia Schmale.

Nature Communications volume 11, Article number: 4924 (2020),


In the central Arctic Ocean the formation of clouds and their properties are sensitive to the availability of cloud condensation nuclei (CCN). The vapors responsible for new particle formation (NPF), potentially leading to CCN, have remained unidentified since the first aerosol measurements in 1991. Here, we report that all the observed NPF events from the Arctic Ocean 2018 expedition are driven by iodic acid with little contribution from sulfuric acid. Iodic acid largely explains the growth of ultrafine particles (UFP) in most events. The iodic acid concentration increases significantly from summer towards autumn, possibly linked to the ocean freeze-up and a seasonal rise in ozone. This leads to a one order of magnitude higher UFP concentration in autumn. Measurements of cloud residuals suggest that particles smaller than 30 nm in diameter can activate as CCN. Therefore, iodine NPF has the potential to influence cloud properties over the Arctic Ocean.

Global airborne sampling reveals a previously unobserved dimethyl sulfide oxidation mechanism in the marine atmosphere

Patrick R. Veres, J. Andrew Neumana, Timothy H. Bertram, Emmanuel Assafa, Glenn M. Wolfed, Christina J. Williamson, Bernadett Weinzierl, Simone Tilmes, Chelsea R. Thompsona, Alexander B. Thames, Jason C. Schroderb, Alfonso Saiz-Lopez, Andrew W. Rollins, James M. Roberts, Derek Price, Jeff Peischl, Benjamin A. Nault, Kristian H. Møller, David O. Miller, Simone Meinardi, Qinyi Li, Jean-François Lamarque, Agnieszka Kupc, Henrik G. Kjaergaard, Douglas Kinnison, Jose L. Jimenez, Christopher M. Jernigan, Rebecca S. Hornbrook, Alan Hill, Maximilian Dollner, Douglas A. Day, Carlos A. Cuevas, Pedro Campuzano-Jost, James Burkholder, T. Paul Bui, William H. Brune, Steven S. Brown, Charles A. Brock, Ilann Bourgeois, Donald R. Blake, Eric C. Apel, and Thomas B. Ryerson

PNAS,, 2020



Dimethyl sulfide (DMS), emitted from the oceans, is the most abundant biological source of sulfur to the marine atmosphere. Atmospheric DMS is oxidized to condensable products that form secondary aerosols that affect Earth’s radiative balance by scattering solar radiation and serving as cloud condensation nuclei. We report the atmospheric discovery of a previously unquantified DMS oxidation product, hydroperoxymethyl thioformate (HPMTF, HOOCH2SCHO), identified through global-scale airborne observations that demonstrate it to be a major reservoir of marine sulfur. Observationally constrained model results show that more than 30% of oceanic DMS emitted to the atmosphere forms HPMTF. Coincident particle measurements suggest a strong link between HPMTF concentration and new particle formation and growth. Analyses of these observations show that HPMTF chemistry must be included in atmospheric models to improve representation of key linkages between the biogeochemistry of the ocean, marine aerosol formation and growth, and their combined effects on climate.

HIOx-IONO2 Dynamics at the Air-Water Interface: Revealing the Existence of a Halogen Bond at the Atmospheric Aerosol Surface

Manoj Kumar, Tarek Trabelsi, Juan Carlos Gomez Martin, Alfonso Saiz-Lopez, and Joseph S.  Francisco

J. Am. Chem. Soc., DOI: 10.1021/jacs.0c05232


Iodine is enriched in marine aerosols, particularly in coastal mid-latitude atmospheric environments, where it initiates the formation of new aerosol particles with iodic acid (HIO3) composition. However, particle formation in polluted and semi-polluted locations is inhibited when the iodine monoxide radical (IO) is intercepted by NO2 to form the iodine nitrate (IONO2). The primary fate of IONO2 is believed to be, besides photolysis, uptake by aerosol surfaces, leading to particulate iodine activation. Herein we have performed Born Oppenheimer molecular dynamics (BOMD) simulations and gas-phase quantum chemical calculations to study the iodine acids-iodine nitrate (HIOx(x = 2 and 3)-IONO2) dynamics at the air-water interface modeled by a water droplet of 191 water molecules. The results indicate that IONO2 does not react directly with these iodine acids, but forms an unu-sual kind of interaction with them within a few picoseconds, which is characterized as halogen bonding. The halogen bond-driven HIO3-IONO2 complex at the air-water interface undergoes deprotonation and exists as IO3--IONO2 anion whereas the HIO2-IONO2 complex does not exhibit any proton loss to the interfacial water molecules. The gas-phase quantum chemical calculations suggest that the HIO3-IONO2 and HIO2-IONO2 complexes have appreciable stabilization energies, which are significantly enhanced upon deprotonation of iodine acids, indicating that these halogen bonds are fairly stable. These IONO2-induced halogen bonds explain the rapid loss of IONO2 to background aerosol. Moreover, they appear to work against iodide formation. Thus, they may play an important role in enhancing the amount of atmospherically non-recyclable iodine (iodate) in marine aerosol.

Inter-comparison of MAX-DOAS measurements of tropospheric HONO slant column densities and vertical profiles during the CINDI-2 campaign

Yang Wang, Arnoud Apituley, Alkiviadis Bais, Steffen Beirle, Nuria Benavent, Alexander Borovski, Ilya Bruchkouski, Ka Lok Chan, Sebastian Donner, Theano Drosoglou, Henning Finkenzeller, Martina M. Friedrich, Udo Frieß, David Garcia-Nieto, Laura Gómez-Martín, François Hendrick, Andreas Hilboll, Junli Jin, Paul Johnston, Theodore K. Koenig, Karin Kreher, Vinod Kumar, Aleksandra Kyuberis, Johannes Lampel, Cheng Liu, Haoran Liu, Jianzhong Ma, Oleg L. Polyansky, Oleg Postylyakov, Richard Querel, Alfonso Saiz-Lopez, Stefan Schmitt, Xin Tian, Jan-Lukas Tirpitz, Michel Van Roozendael, Rainer Volkamer, Zhuoru Wang, Pinhua Xie, Chengzhi Xing, Jin Xu, Margarita Yela, Chengxin Zhang and Thomas Wagner

Atmos. Meas. Tech., 13, 5087–5116, 2020,


We present the inter-comparison of delta slant column densities (SCDs) and vertical profiles of nitrous acid (HONO) derived from measurements of different multi-axis differential optical absorption spectroscopy (MAX-DOAS) instruments and using different inversion algorithms during the Second Cabauw Inter-comparison campaign for Nitrogen Dioxide measuring Instruments (CINDI-2) in September 2016 at Cabauw, the Netherlands (51.97∘ N, 4.93∘ E). The HONO vertical profiles, vertical column densities (VCDs), and near-surface volume mixing ratios are compared between different MAX-DOAS instruments and profile inversion algorithms for the first time. Systematic and random discrepancies of the HONO results are derived from the comparisons of all data sets against their median values. Systematic discrepancies of HONO delta SCDs are observed in the range of ±0.3×1015 molec. cm−2, which is half of the typical random discrepancy of 0.6×1015 molec. cm−2. For a typical high HONO delta SCD of 2×1015 molec. cm−2, the relative systematic and random discrepancies are about 15 % and 30 %, respectively. The inter-comparison of HONO profiles shows that both systematic and random discrepancies of HONO VCDs and near-surface volume mixing ratios (VMRs) are mostly in the range of ∼±0.5×1014 molec. cm−2 and ∼±0.1 ppb (typically ∼20 %). Further we find that the discrepancies of the retrieved HONO profiles are dominated by discrepancies of the HONO delta SCDs. The profile retrievals only contribute to the discrepancies of the HONO profiles by ∼5 %. However, some data sets with substantially larger discrepancies than the typical values indicate that inappropriate implementations of profile inversion algorithms and configurations of radiative transfer models in the profile retrievals can also be an important uncertainty source. In addition, estimations of measurement uncertainties of HONO dSCDs, which can significantly impact profile retrievals using the optimal estimation method, need to consider not only DOAS fit errors, but also atmospheric variability, especially for an instrument with a DOAS fit error lower than ∼3×1014 molec. cm−2. The MAX-DOAS results during the CINDI-2 campaign indicate that the peak HONO levels (e.g. near-surface VMRs of ∼0.4 ppb) often appeared in the early morning and below 0.2 km. The near-surface VMRs retrieved from the MAX-DOAS observations are compared with those measured using a co-located long-path DOAS instrument. The systematic differences are smaller than 0.15 and 0.07 ppb during early morning and around noon, respectively. Since true HONO values at high altitudes are not known in the absence of real measurements, in order to evaluate the abilities of profile inversion algorithms to respond to different HONO profile shapes, we performed sensitivity studies using synthetic HONO delta SCDs simulated by a radiative transfer model with assumed HONO profiles. The tests indicate that the profile inversion algorithms based on the optimal estimation method with proper configurations can reproduce the different HONO profile shapes well. Therefore we conclude that the features of HONO accumulated near the surface derived from MAX-DOAS measurements are expected to represent the ambient HONO profiles well.

Intercomparison of NO2, O4, O3 and HCHO slant column measurements by MAX-DOAS and zenith-sky UV–visible spectrometers during CINDI-2

Karin Kreher, Michel Van Roozendael, Francois Hendrick, Arnoud Apituley, Ermioni Dimitropoulou, Udo Frieß, Andreas Richter, Thomas Wagner, Johannes Lampel, Nader Abuhassan, Li Ang, Monica Anguas, Alkis Bais, Nuria Benavent, Tim Bösch, Kristof Bognar, Alexander Borovski, Ilya Bruchkouski, Alexander Cede, Ka Lok Chan1, Sebastian Donner, Theano Drosoglou, Caroline Fayt, Henning Finkenzeller, David Garcia-Nieto, Clio Gielen, Laura Gómez-Martín, Nan Hao, Bas Henzing, Jay R. Herman, Christian Hermans, Syedul Hoque, Hitoshi Irie, Junli Jin, Paul Johnston, Junaid Khayyam Butt, Fahim Khokhar, Theodore K. Koenig, Jonas Kuhn, Vinod Kumar, Cheng Liu, Jianzhong Ma, Alexis Merlaud, Abhishek K. Mishra, Moritz Müller, Monica Navarro-Comas, Mareike Ostendorf, Andrea Pazmino, Enno Peters, Gaia Pinardi, Manuel Pinharanda, Ankie Piters, Ulrich Platt, Oleg Postylyakov, Cristina Prados-Roman, Olga Puentedura, Richard Querel, Alfonso Saiz-Lopez, Anja Schönhardt, Stefan F. Schreier, André Seyler, Vinayak Sinha, Elena Spinei, Kimberly Strong, Frederik Tack, Xin Tian, Martin Tiefengraber, Jan-Lukas Tirpitz, Jeroen van Gent, Rainer Volkamer, Mihalis Vrekoussis, Shanshan Wang, Zhuoru Wang, Mark Wenig, Folkard Wittrock, Pinhua H. Xie, Jin Xu, Margarita Yela, Chengxin Zhang, and Xiaoyi Zhao

Atmos. Meas. Tech., 13, 2169–2208, 2020


In September 2016, 36 spectrometers from 24 institutes measured a number of key atmospheric pollutants for a period of 17 d during the Second Cabauw Intercomparison campaign for Nitrogen Dioxide measuring Instruments (CINDI-2) that took place at Cabauw, the Netherlands (51.97∘ N, 4.93∘ E). We report on the outcome of the formal semi-blind intercomparison exercise, which was held under the umbrella of the Network for the Detection of Atmospheric Composition Change (NDACC) and the European Space Agency (ESA). The three major goals of CINDI-2 were (1) to characterise and better understand the differences between a large number of multi-axis differential optical absorption spectroscopy (MAX-DOAS) and zenith-sky DOAS instruments and analysis methods, (2) to define a robust methodology for performance assessment of all participating instruments, and (3) to contribute to a harmonisation of the measurement settings and retrieval methods. This, in turn, creates the capability to produce consistent high-quality ground-based data sets, which are an essential requirement to generate reliable long-term measurement time series suitable for trend analysis and satellite data validation.

The data products investigated during the semi-blind intercomparison are slant columns of nitrogen dioxide (NO2), the oxygen collision complex (O4) and ozone (O3) measured in the UV and visible wavelength region, formaldehyde (HCHO) in the UV spectral region, and NO2 in an additional (smaller) wavelength range in the visible region. The campaign design and implementation processes are discussed in detail including the measurement protocol, calibration procedures and slant column retrieval settings. Strong emphasis was put on the careful alignment and synchronisation of the measurement systems, resulting in a unique set of measurements made under highly comparable air mass conditions.

The CINDI-2 data sets were investigated using a regression analysis of the slant columns measured by each instrument and for each of the target data products. The slope and intercept of the regression analysis respectively quantify the mean systematic bias and offset of the individual data sets against the selected reference (which is obtained from the median of either all data sets or a subset), and the rms error provides an estimate of the measurement noise or dispersion. These three criteria are examined and for each of the parameters and each of the data products, performance thresholds are set and applied to all the measurements. The approach presented here has been developed based on heritage from previous intercomparison exercises. It introduces a quantitative assessment of the consistency between all the participating instruments for the MAX-DOAS and zenith-sky DOAS techniques.

Modeling the Impact of Marine DMS Emissions on Summertime Air Quality Over the Coastal East China Seas

Shanshan Li, Golam Sarwar, Junri Zhao, Yan Zhang, Shengqian Zhou, Ying Chen, Guipeng Yang and Alfonso Saiz‐Lopez.

Earth and Space Science, Volume7, Issue10,, 2020.


Biogenic emission of dimethyl sulfide (DMS) from seawater is the major natural source of sulfur into the atmosphere. In this study, we use an advanced air quality model (CMAQv5.2) with DMS chemistry to examine the impact of DMS emissions from seawater on summertime air quality over China. A national scale database of DMS concentration in seawater is established based on a 5‐year observational record in the East China seas including the Bohai Sea, the Yellow Sea, and the East China Sea. We employ a commonly used global database and also the newly developed local database of oceanic DMS concentration, calculate DMS emissions using three different parameterization schemes, and perform five different model simulations for July, 2018. Results indicate that in large coastal areas of China, the average DMS emissions flux obtained with the local database is 3 times higher than that resulting from the global database, with a mean value of 9.1 μmol m−2 day−1 in the Bohai Sea, 8.4 μmol m−2 day−1 in the Yellow Sea, and 13.4 μmol m−2 day−1 in the East China Sea. The total DMS emissions flux calculated with the Nightingale scheme is 42% higher than that obtained with the Liss and Merlivat scheme but is 15% lower than that obtained with the Wanninkhof scheme. Among the three parameterizations, results of the Liss and Merlivat scheme agree better with the ship‐based observations over China's coastal waters. DMS emissions with the Liss and Merlivat parametrization increase atmospheric sulfur dioxide (SO2) and sulfate (SO42−) concentration over the East China seas by 6.4% and 3.3%, respectively. Our results indicate that although the anthropogenic source is still the dominant contributor of atmospheric sulfur burden in China, biogenic DMS emissions source is nonnegligible.

Natural halogens buffer tropospheric ozone in a changing climate

Fernando lglesias-Suarez, Alba Badia, Rafael P. Fernandez, Carlos A. Cuevas, Douglas E. Kinnison, Simone Tilmes, Jean-François Lamarque, Mathew  C. Long, Ryan Hossaini and Alfonso Saiz-Lopez

Nat. Clim. Chang.,, 2020



Reactive atmospheric halogens destroy tropospheric ozone (O3), an air pollutant and greenhouse gas. The primary source of natural halogens is emissions from marine phytoplankton and algae, as well as abiotic sources from ocean and tropospheric chemistry, but how their fluxes will change under climate warming, and the resulting impacts on O3, are not well known. Here, we use an Earth system model to estimate that natural halogens deplete approximately 13% of tropospheric O3 in the present-day climate. Despite increased levels of natural halogens through the twenty-first century, this fraction remains stable due to compensation from hemispheric, regional and vertical heterogeneity in tropospheric O3 loss. Notably, this halogen-driven O3 buffering is projected to be greatest over polluted and populated regions, due mainly to iodine chemistry, with important implications for air quality.

Observationally constrained modeling of atmospheric oxidationcapacity and photochemical reactivity in Shanghai, China

Jian Zhu, Shanshan Wang, Hongli Wang, Shengao Jing, Shengrong Lou, Alfonso Saiz-Lopez, and Bin Zhou

Atmos. Chem. Phys., 20, 1217–1232, 2020



An observation-based model coupled to the Master Chemical Mechanism (V3.3.1) and constrained by a full suite of observations was developed to study atmospheric oxidation capacity (AOC), OH reactivity, OH chain length and HOx (=OH+HO2) budget for three different ozone (O3) concentration levels in Shanghai, China. Five months of observations from 1 May to 30 September 2018 showed that the air quality level is lightly polluted or worse (Ambient Air Quality Index, AQI, of > 100) for 12 d, of which ozone is the primary pollutant for 10 d, indicating ozone pollution was the main air quality challenge in Shanghai during summer of 2018. The levels of ozone and its precursors, as well as meteorological parameters, revealed the significant differences among different ozone levels, indicating that the high level of precursors is the precondition of ozone pollution, and strong radiation is an essential driving force. By increasing the input JNO2 value by 40 %, the simulated O3 level increased by 30 %–40 % correspondingly under the same level of precursors. The simulation results show that AOC, dominated by reactions involving OH radicals during the daytime, has a positive correlation with ozone levels. The reactions with non-methane volatile organic compounds (NMVOCs; 30 %–36 %), carbon monoxide (CO; 26 %–31 %) and nitrogen dioxide (NO2; 21 %–29 %) dominated the OH reactivity under different ozone levels in Shanghai. Among the NMVOCs, alkenes and oxygenated VOCs (OVOCs) played a key role in OH reactivity, defined as the inverse of the OH lifetime. A longer OH chain length was found in clean conditions primarily due to low NO2 in the atmosphere. The high level of radical precursors (e.g., O3, HONO and OVOCs) promotes the production and cycling of HOx, and the daytime HOx primary source shifted from HONO photolysis in the morning to O3 photolysis in the afternoon. For the sinks of radicals, the reaction with NO2 dominated radical termination during the morning rush hour, while the reactions of radical–radical also contributed to the sinks of HOx in the afternoon. Furthermore, the top four species contributing to ozone formation potential (OFP) were HCHO, toluene, ethylene and m/p-xylene. The concentration ratio (∼23 %) of these four species to total NMVOCs is not proportional to their contribution (∼55 %) to OFP, implying that controlling key VOC species emission is more effective than limiting the total concentration of VOC in preventing and controlling ozone pollution.

Photochemistry of oxidized Hg(I) and Hg(II) species suggests missing mercury oxidation in the troposphere

Alfonso Saiz-Lopez, Oleg Travnikov, Jeroen E. Sonke, Colin P. Thackray, Daniel J. Jacob, Javier Carmona-García, Antonio Francés-Monerris, Daniel Roca-Sanjuán, A. Ulises Acuña, Juan Z. Dávalos, Carlos A. Cuevas, Martin Jiskra, Feiyue Wang, Johannes Bieser, John M. C. Plane and Joseph S. Francisco

PNAS November 23, 2020;

Abstract:Mercury (Hg), a global contaminant, is emitted mainly in its elemental form Hg0 to the atmosphere where it is oxidized to reactive HgII compounds, which efficiently deposit to surface ecosystems. Therefore, the chemical cycling between the elemental and oxidized Hg forms in the atmosphere determines the scale and geographical pattern of global Hg deposition. Recent advances in the photochemistry of gas-phase oxidized HgI and HgII species postulate their photodissociation back to Hg0 as a crucial step in the atmospheric Hg redox cycle. However, the significance of these photodissociation mechanisms on atmospheric Hg chemistry, lifetime, and surface deposition remains uncertain. Here we implement a comprehensive and quantitative mechanism of the photochemical and thermal atmospheric reactions between Hg0, HgI, and HgII species in a global model and evaluate the results against atmospheric Hg observations. We find that the photochemistry of HgI and HgII leads to insufficient Hg oxidation globally. The combined efficient photoreduction of HgI and HgII to Hg0 competes with thermal oxidation of Hg0, resulting in a large model overestimation of 99% of measured Hg0 and underestimation of 51% of oxidized Hg and ∼66% of HgII wet deposition. This in turn leads to a significant increase in the calculated global atmospheric Hg lifetime of 20 mo, which is unrealistically longer than the 3–6-mo range based on observed atmospheric Hg variability. These results show that the HgI and HgII photoreduction processes largely offset the efficiency of bromine-initiated Hg0 oxidation and reveal missing Hg oxidation processes in the troposphere.


Photodissociation Mechanisms of Major Mercury(II) Species in the Atmospheric Chemical Cycle of Mercury

Antonio Francés‐Monerris, Javier Carmona‐García, A. Ulises Acuña, Juan Z. Dávalos, Carlos A. Cuevas, Douglas E. Kinnison, Joseph S. Francisco, Alfonso Saiz‐Lopez and Daniel Roca‐Sanjuán

Angew.Chem. Int.Ed. 2020, 59,7605 –7610


Mercury is a contaminant of global concern that is transported throughout the atmosphere as elemental mercury Hg0 and its oxidized forms HgI and HgII. The efficient gas‐phase photolysis of HgII and HgI has recently been reported. However, whether the photolysis of HgII leads to other stable HgII species, to HgI, or to Hg0 and its competition with thermal reactivity remain unknown. Herein, we show that all oxidized forms of mercury rapidly revert directly and indirectly to Hg0 by photolysis. Results are based on non‐adiabatic dynamics simulations, in which the photoproduct ratios were determined with maximum errors of 3%. We construct for the first time a complete quantitative mechanism of the photochemical and thermal conversion between atmospheric HgII, HgI, and Hg0 compounds. These results reveal new fundamental chemistry that has broad implications for the global atmospheric Hg cycle. Thus, photoreduction clearly competes with thermal oxidation, with Hg0 being the main photoproduct of HgII photolysis in the atmosphere, which significantly increases the lifetime of this metal in the environment.

Potential Effect of Halogens on Atmospheric Oxidation and Air Quality in China

Qinyi Li, Alba Badia, Tao Wang, Golam Sarwar, Xiao Fu, Li Zhang, Qiang Zhang, Jimmy Fung, Carlos A. Cuevas, Shanshan Wang, Bin Zhou and Alfonso Saiz‐Lopez

Journal of Geophysical Research: Atmospheres, 125, e2019JD032058


Air pollution has been a hazard in China over recent decades threatening the health of half a billion people. Much effort has been devoted to mitigating air pollution in China leading to a significant reduction in primary pollutants emissions from 2013 to 2017, while a continuously worsening trend of surface ozone (O3, a secondary pollutant and greenhouse gas) was observed over the same period. Atmospheric oxidation, dominated by daytime reactions involving hydroxyl radicals (OH), is the critical process to convert freshly‐emitted compounds into secondary pollutants, and is underestimated in current models of China's air pollution. Halogens (chlorine, bromine, and iodine) are known to profoundly influence oxidation chemistry in the marine environment; however, their impact on atmospheric oxidation and air pollution in China is unknown. In the present study, we report for the first time that halogens substantially enhance the total atmospheric oxidation capacity in polluted areas of China, typically 10% to 20% (up to 87% in winter) and mainly by significantly increasing OH level. The enhanced oxidation along the coast is driven by oceanic emissions, and that over the inland areas by anthropogenic emission. The extent and seasonality of halogen impact are largely explained by the dynamics of Asian monsoon, location and intensity of halogen emissions, and O3 formation regime. The omission of halogen emissions and chemistry may lead to significant errors in historical re‐assessments and future projections of the evolution of atmospheric oxidation in polluted regions.

Quantitative detection of iodine in the stratosphere

Theodore K. Koenig, Sunil Baidar, Pedro Campuzano-Jost, Carlos A. Cuevas, Barbara Dix, Rafael P. Fernandez, Hongyu Guo, Samuel R. Halle, Douglas Kinnisone, Benjamin A. Nault, , Kirk Ullmanne, Jose L. Jimenez, Alfonso Saiz-Lopez, and Rainer Volkamer

PNAS, 117 (4) 1860-1866,



Oceanic emissions of iodine destroy ozone, modify oxidative capacity, and can form new particles in the troposphere. However, the impact of iodine in the stratosphere is highly uncertain due to the lack of previous quantitative measurements. Here, we report quantitative measurements of iodine monoxide radicals and particulate iodine (Iy,part) from aircraft in the stratosphere. These measurements support that 0.77 ± 0.10 parts per trillion by volume (pptv) total inorganic iodine (Iy) is injected to the stratosphere. These high Iy amounts are indicative of active iodine recycling on ice in the upper troposphere (UT), support the upper end of recent Iy estimates (0 to 0.8 pptv) by the World Meteorological Organization, and are incompatible with zero stratospheric iodine injection. Gas-phase iodine (Iy,gas) in the UT (0.67 ± 0.09 pptv) converts to Iy,part sharply near the tropopause. In the stratosphere, IO radicals remain detectable (0.06 ± 0.03 pptv), indicating persistent Iy,part recycling back to Iy,gas as a result of active multiphase chemistry. At the observed levels, iodine is responsible for 32% of the halogen-induced ozone loss (bromine 40%, chlorine 28%), due primarily to previously unconsidered heterogeneous chemistry. Anthropogenic (pollution) ozone has increased iodine emissions since preindustrial times (ca. factor of 3 since 1950) and could be partly responsible for the continued decrease of ozone in the lower stratosphere. Increasing iodine emissions have implications for ozone radiative forcing and possibly new particle formation near the tropopause.

Regional and Urban-Scale Environmental Influences of Oceanic DMS Emissions over Coastal China Seas

Shanshan Li, Yan Zhang, Junri Zhao, Golam Sarwar, Shengqian Zhou, Ying Chen, Guipeng Yang and Alfonso Saiz-Lopez

Atmosphere 2020, 11, 849; doi:10.3390/atmos11080849


Marine biogenic dimethyl sulfide (DMS) is an important natural source of sulfur in the atmosphere, which may play an important role in air quality. In this study, the WRF-CMAQ model is employed to assess the impact of DMS on the atmospheric environment at the regional scale of eastern coastal China and urban scale of Shanghai in 2017. A national scale database of DMS concentration in seawater is established based on the historical DMS measurements in the Yellow Sea, the Bohai Sea and the East China Sea in different seasons during 2009~2017. Results indicate that the sea-to-air emission flux of DMS varies greatly in different seasons, with the highest in summer, followed by spring and autumn, and the lowest in winter. The annual DMS emissions from the Yellow Sea, the Bohai Sea and the East China Sea are 0.008, 0.059, and 0.15 Tg S a−1, respectively. At the regional scale, DMS emissions increase atmospheric sulfur dioxide (SO2) and sulfate (SO2−4) concentrations over the East China seas by a maximum of 8% in summer and a minimum of 2% in winter, respectively. At the urban scale, the addition of DMS emissions increase the SO2 and SO2−4 levels by 2% and 5%, respectively, and reduce ozone (O3) in the air of Shanghai by 1.5%~2.5%. DMS emissions increase fine-mode ammonium particle concentration distribution by 4% and 5%, and fine-mode nss-SO2−4 concentration distributions by 4% and 9% in the urban and marine air, respectively. Our results indicate that although anthropogenic sources are still the dominant contributor of atmospheric sulfur burden in China, biogenic DMS emissions source cannot be ignored.

Revising the Ozone Depletion Potentials Metric for Short‐Lived Chemicals Such as CF3I and CH3I

Jun Zhang, Donald J. Wuebbles, Douglas E. Kinnison and Alfonso Saiz‐Lopez

Journal of Geophysical Research: Atmospheres, 125, e2020JD032414


Ozone depletion potentials (ODPs) are an important metric in national and international policy for evaluating the relative importance of different gases to affecting stratospheric ozone. In evaluating the ODPs of iodotrifluoromethane (CF3I) and methyl iodide (CH3I) using the recently updated understanding of atmospheric iodine chemistry, only minor ozone loss would be expected to occur in the stratosphere from the very short‐lived (~6 days) CF3I, with slightly larger destruction of stratospheric ozone from CH3I (~12 days). In addition, most of the ozone destruction would likely occur in the lower troposphere over continental surfaces, reducing anthropogenic ozone pollution. The traditional ODP concept uses total column ozone change, but this is not an accurate representation of potential future use of very short‐lived substances (VSLSs) on the abundance of stratospheric ozone. A new metric, Stratospheric ODP (or SODP), is defined that only accounts for stratospheric ozone loss, providing a useful additional tool for policy considerations of VSLSs on stratospheric ozone.

Seasonal impact of biogenic very short-lived bromocarbons on lowermost stratospheric ozone between 60_ N and 60_ S during the 21st century

Javier Alejandro Barrera, Rafael Pedro Fernandez, Fernando Iglesias-Suarez, Carlos Alberto Cuevas, Jean-Francois Lamarque, and Alfonso Saiz-Lopez

Atmos. Chem. Phys., 20, 8083–8102, 2020,



Biogenic very short-lived bromocarbons (VSLBr) currently represent ∼25 % of the total stratospheric bromine loading. Owing to their much shorter lifetime compared to anthropogenic long-lived bromine (e.g. halons) and chlorine (e.g. chlorofluorocarbons), the impact of VSLBr on ozone peaks in the lowermost stratosphere, which is a key climatic and radiative atmospheric region. Here we present a modelling study of the evolution of stratospheric ozone and its chemical loss within the tropics and at mid-latitudes during the 21st century. Two different experiments are explored: considering and neglecting the additional stratospheric injection of 5 ppt biogenic bromine naturally released from the ocean. Our analysis shows that the inclusion of VSLBr results in a realistic stratospheric bromine loading and improves the agreement between the model and satellite observations of the total ozone column (TOC) for the 1980–2015 period at mid-latitudes. We show that the overall ozone response to VSLBr at mid-latitudes follows the stratospheric evolution of long-lived inorganic chlorine and bromine throughout the 21st century. Additional ozone loss due to VSLBr is maximized during the present-day period (1990–2010), with TOC differences of −8 DU (−3 %) and −5.5 DU (−2 %) for the Southern Hemisphere and Northern Hemisphere mid-latitudes (SH-MLs and NH-MLs), respectively. Moreover, the projected TOC differences at the end of the 21st century are ∼50 % lower than the values found for the present-day period.

We find that seasonal VSLBr impact on lowermost stratospheric ozone at mid-latitude is influenced by the seasonality of the heterogeneous inorganic-chlorine reactivation processes on ice crystals. Indeed, due to the more efficient reactivation of chlorine reservoirs (mainly ClONO2 and HCl) within the colder SH-ML lowermost stratosphere, the seasonal VSLBr impact shows a small but persistent hemispheric asymmetry through the whole modelled period. Our results indicate that, although the overall VSLBr-driven ozone destruction is greatest during spring, the halogen-mediated (Halogx-Loss) ozone loss cycle in the mid-latitude lowermost stratosphere during winter is comparatively more efficient than the HOx cycle with respect to other seasons. Indeed, when VSLBr are considered, Halogx-Loss dominates wintertime lowermost stratospheric ozone loss at SH-MLs between 1985 and 2020, with a contribution of inter-halogen ClOx–BrOx cycles to Halogx-Loss of ∼50 %.

Within the tropics, a small (<−2.5

 DU) and relatively constant (∼−1 %) ozone depletion mediated by VSLBr is closely related to their fixed emissions throughout the modelled period. By including the VSLBr sources, the seasonal Halogx-Loss contribution to lowermost stratospheric ozone loss is practically dominated by the BrOx cycle, reflecting the low sensitivity of very short-lived (VSL) bromine to background halogen abundances to drive tropical stratospheric ozone depletion. We conclude that the link between biogenic bromine sources and seasonal changes in heterogeneous chlorine reactivation is a key feature for future projections of mid-latitude lowermost stratospheric ozone during the 21st century.

Spatio-temporal variations in NO2 and SO2 over Shanghai and Chongming Eco Island measured by Ozone Monitoring Instrument (OMI) during 2008-2017

Ruibin Xue, Shanshan Wang, Danran Li, Zhong Zou, Ka Lok Chan, Pieter Valks, Alfonso Saiz-Lopez, Bin Zhou

Journal of Cleaner Production, Volume 258, 120563,



High resolution satellite maps are useful for the identification of pollution hotspots. In this work, nitrogen dioxide (NO2) and sulfur dioxide (SO2) observations from the Ozone Monitoring Instrument (OMI) have been averaged and gridded for Shanghai and surrounding areas with a spatial resolution of 0.01° × 0.01°. The pollution maps have been used to investigate the spatio-temporal variations in NO2 and SO2 from 2008 to 2017. The averaged tropospheric NO2 and planetary boundary layer (PBL) SO2 columns in Shanghai are on average 1.40 × 1016 molec·cm−2 and 1.21 × 1016 molec·cm−2, respectively. As the government has put a lot of effort to improve the air quality, both the NO2 and SO2 columns reveal a significant decline in Shanghai during the past decade, with a reduction of ∼24% and ∼56%, respectively, which is also confirmed by the good agreement between satellite observations and ground-based in-situ measurements. The NO2 and SO2 time series also show distinct seasonal characteristics with higher pollution level during winter and lower in the summer. Due to the impact of ship and industrial emissions, the hotspots of NO2 and SO2 are concentrated in the northern part of Shanghai, while the pollution level is lower in the southern and eastern regions. Decreasing trends in NO2 and SO2 are found for most areas of Shanghai during the past decade, though the strongest decrease in the northern part of the city (1.4 × 1015 molec·cm−2·year−1 for NO2 and 3.0 × 1015 molec·cm−2·year−1 for SO2). Comparisons with the China Multi-Resolution Emissions Inventory (MEIC) indicate that the driving factors for the decline of NO2 and SO2 are mainly denitration and desulfurization in the power sector, and the reduction of emissions in the industry sector. We also use aerosol optical depth (AOD) measurements from MODerate-resolution Imaging Spectroradiometer (MODIS) to investigate the relationship between gas phase pollutants and formation of secondary aerosol. Compared to SO2, the contribution of NO2 to secondary aerosol formation increased in the central part of Shanghai. Although Chongming Eco-Island has developed rapidly in recent years, both the SO2 and NO2 levels decreased significantly. This is mainly related to the strict emission control policy and improved urban planning, and indicates that ecological development is achievable under the guidance of policies.

Tropospheric Ozone Assessment Report: A critical review of changes in the tropospheric ozone burden and budget from 1850 to 2100

A. T. Archibald, J. L. Neu, Y. F. Elshorbany, O. R. Cooper, P. J. Young, H. Akiyoshi, R. A. Cox, M. Coyle, R. G. Derwent, M. Deushi, A. Finco, G. J. Frost, I. E. Galbally, G. Gerosa, C. Granier, P. T. Griffiths, R. Hossaini, L. Hu, P. Jo¨ckel, B. Josse, M. Y. Lin, M. Mertens, O. Morgenstern, M. Naja, V. Naik, S. Oltmans, D. A. Plummer, L. E. Revell, A. Saiz-Lopez, P. Saxena, Y. M. Shin, I. Shahid, D. Shallcross, S. Tilmes, T. Trickl, T. J. Wallington, T. Wang, H. M. Worden, and G. Zeng.

Elem. Sci. Anth. 8: 1. DOI:, 2020.


Our understanding of the processes that control the burden and budget of tropospheric ozone has changed dramatically over the last 60 years. Models are the key tools used to understand these changes, and these underscore that there are many processes important in controlling the tropospheric ozone budget. In this critical review, we assess our evolving understanding of these processes, both physical and chemical. We review model simulations from the International Global Atmospheric Chemistry Atmospheric Chemistry and Climate Model Intercomparison Project and Chemistry Climate Modelling Initiative to assess the changes in the tropospheric ozone burden and its budget from 1850 to 2010. Analysis of these data indicates that there has been significant growth in the ozone burden from 1850 to 2000 (approximately 43 ± 9%) but smaller growth between 1960 and 2000 (approximately 16 ± 10%) and that the models simulate burdens of ozone well within recent satellite estimates. The Chemistry Climate Modelling Initiative model ozone budgets indicate that the net chemical production of ozone in the troposphere plateaued in the 1990s and has not changed since then inspite of increases in the burden. There has been a shift in net ozone production in the troposphere being greatest in the northern mid and high latitudes to the northern tropics, driven by the regional evolution of precursor emissions. An analysis of the evolution of tropospheric ozone through the 21st century, as simulated by Climate Model Intercomparison Project Phase 5 models, reveals a large source of uncertainty associated with models themselves (i.e., in the way that they simulate the chemical and physical processes that control tropospheric ozone). This structural uncertainty is greatest in the near term (two to three decades), but emissions scenarios dominate uncertainty in the longer term (2050–2100) evolution of tropospheric ozone. This intrinsic model uncertainty prevents robust predictions of near-term changes in the tropospheric ozone burden, and we review how progress can be made to reduce this limitation.

Understanding atmospheric methane sub-seasonal variability over India.

Yogesh K. Tiwari, Tania Guha, Vinu Valsala, Alfonso Saiz Lopez, Carlos Cuevas, Rafael P. Fernandez, Anoop S. Mahajan.

Atmospheric Environment, Volume 223, 117206,, 2020



Atmospheric methane (CH4) is considered to be one of the most important greenhouse gases due to its increasing atmospheric concentrations and the fact that it has a warming potential 28 times that of atmospheric carbon dioxide (CO2). Over the Indian sub-continent, fluxes and transport both contribute towards CH4 seasonal variability. Its intra-seasonal variability however is more complex as it is additionally influenced by monsoonal activity during the Asian Summer Monsoon (ASM) period. In this study, the intra-seasonal variability of atmospheric CH4 is examined using ground-based observations at two sites located in the Southern Indian Peninsula, Sinhagad (SNG) and Cape Rama (CRI); and outputs from three different model simulations. Both, the ground based observations and multi-model simulations show that the dominant spectral variability of CH4 is coherent with 20–90 day oscillations in the dynamics of the monsoon (termed hereafter as Intra-Seasonal Oscillations, ISOs). The multi-model analysis revealed that CH4 is heavily influenced by advection due to this intra-seasonal variability. The simulations also display a clear northward propagation of CH4 anomalies over India. The co-evolution of CH4, outgoing long wave radiation (to represent convection) and OH radicals (proxy to CH4 sinks) is presented. The study quantifies CH4 variability at intra-seasonal timescales and also its spatial extent. The results suggest that the effect of ISOs on CH4 needs to be considered along with the corresponding observations for future inverse modeling.

A 120 000-year record of sea ice in the North Atlantic?

Niccolò Maffezzoli, Paul Vallelonga, Ross Edwards, Alfonso Saiz-Lopez, Clara Turetta, Helle Astrid Kjær,Carlo Barbante, Bo Vinther, and Andrea Spolaor

Clim. Past, 15, 2031–2051,, 2019



Although it has been demonstrated that the speedand magnitude of the recent Arctic sea ice decline is un-precedented for the past 1450 years, few records are avail-able to provide a paleoclimate context for Arctic sea ice ex-tent. Bromine enrichment in ice cores has been suggestedto indicate the extent of newly formed sea ice areas. De-spite the similarities among sea ice indicators and ice corebromine enrichment records, uncertainties still exist regard-ing the quantitative linkages between bromine reactive chem-istry and the first-year sea ice surfaces. Here we present a120 000-year record of bromine enrichment from the RE-CAP (REnland ice CAP) ice core, coastal east Greenland,and interpret it as a record of first-year sea ice. We compareit to existing sea ice records from marine cores and tenta-tively reconstruct past sea ice conditions in the North At-lantic as far north as the Fram Strait (50–85◦N). Our inter-pretation implies that during the last deglaciation, the transi-tion from multi-year to first-year sea ice started at∼17.5 ka,synchronously with sea ice reductions observed in the east-ern Nordic Seas and with the increase in North Atlanticocean temperature. First-year sea ice reached its maximumat 12.4–11.8 ka during the Younger Dryas, after which open-water conditions started to dominate, consistent with sea icerecords from the eastern Nordic Seas and the North Icelandicshelf. Our results show that over the last 120 000 years, multi-year sea ice extent was greatest during Marine Isotope Stage(MIS) 2 and possibly during MIS 4, with more extended first-year sea ice during MIS 3 and MIS 5. Sea ice extent duringthe Holocene (MIS 1) has been less than at any time in thelast 120 000 years.

Ab initio quantum-chemical computations of the absorption cross sections of HgX2 and HgXY (X, Y = Cl, Br, and I): molecules of interest in the Earth's atmosphere

Sebastian P. Sitkiewicz, Daniel Rivero, Josep M. Oliva-Enrich, Alfonso Saiz-Lopez and Daniel Roca-Sanjuán

Phys. Chem. Chem. Phys., doi: 10.1039/c8cp06160b, 2018.



The electronic-structure properties of the low-lying electronic states and the absorption cross sections (σ(E)) of mercury halides HgCl2, HgBr2, HgI2, HgBrCl, HgClI, and HgBrI have been determined within the UV-vis spectrum range (170 nm ≤ λphoton ≤ 600 nm) by means of the DKH3-MS-CASPT2/SO-RASSI quantum-chemical methodology (with the ANO-RCC basis set) and a semi-classical computational strategy based on nuclear sampling for simulating the band shapes. Computed band energies show a good agreement with the available experimental data for HgX2 with errors around 0.1–0.2 eV; theoretical and σ(E) are within the same order of magnitude. For the mixed HgXY compounds, the present computed data allow us to interpret previously proposed absorption bands estimated from the spectra of the parent molecules HgX2 and HgY2, measured in methanol solution. The analyses performed on the excited-state electronic structure and its changes around the Franck–Condon region provide a rationale on the singlet–triplet mixing of the absorption bands and the heavy-atom effect of the Hg compounds. Furthermore, the present benchmark of HgX2 and HgXY absorption σ values together with the previous benchmark of the electronic-structure properties of HgBr2 [see S. P. Sitkiewicz, et al., J. Chem. Phys., 2016, 145, 244304] has been helpful to set up a methodological and computational protocol which shall be used for predicting the atmospheric absorption and photolysis properties of several Hg compounds present in the atmospheric cycle of Hg.

Direct quantification of inorganic iodine in seawater by mixed-mode liquid chromatography-electrospray ionization-mass spectrometry)

M. Hernáiz-Izquierdo, P. Galindo-Iranzo, M.P. García-Armada, A. Saiz-López, B. Gómara, J.E. Quintanilla-López, R. Lebrón-Aguilar

Journal of Chromatography A, Volume 1588, 15 March 2019, Pages 99-107, 2019



Atmospheric iodine plays a relevant role in climate change. Bearing in mind that most of this iodine comes from the oceans, analytical methods capable of determining iodine in a challenging matrix as seawater are necessary. In this work, the first method capable of direct determination of total inorganic iodine in seawater at subnanomolar level based on mixed-mode liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) without any sample treatment is presented.

Analytical characteristics of the developed method were studied in terms of linear range, limits of detection and quantification, precision, trueness, matrix effect, and robustness. The detection limit for iodide was as low as 0.16 nM, injecting 5 μL of seawater without any sample treatment and the working linear range of four orders of magnitude was wide enough to cover the broad concentration range observed in seawater samples. Average values for repeatability and intermediate precision were 4.1% and 8.1%, respectively. The suitability of the method was demonstrated through its application to the analysis of several types of samples, including seawater samples taken at different locations along the Spanish Mediterranean coast and some domestic iodized salts.

According to the results obtained, the method developed is rapid, easy to apply and to be automated, avoids sample treatment and requires only few microliters of sample. Furthermore, it has a low detection limit and allows the quantification of inorganic iodine over a wide concentration range.

Diurnal cycle of iodine, bromine, and mercury concentrations in Svalbard surface snow

Andrea Spolaor, Elena Barbaro, David Cappelletti, Clara Turetta, Mauro Mazzola, Fabio Giardi, Mats P. Björkman, Federico Lucchetta, Federico Dallo, Katrine Aspmo Pfaffhuber, Hélène Angot, Aurelien Dommergue, Marion Maturilli, Alfonso Saiz-Lopez, Carlo Barbante, and Warren R. L. Cairns

Atmos. Chem. Phys., 19, 13325–13339, 2019,



Sunlit snow is highly photochemically active and plays a key role in the exchange of gas phase species between the cryosphere and the atmosphere. Here, we investigate the behaviour of two selected species in surface snow: mercury (Hg) and iodine (I). Hg can deposit year-round and accumulate in the snowpack. However, photo-induced re-emission of gas phase Hg from the surface has been widely reported. Iodine is active in atmospheric new particle formation, especially in the marine boundary layer, and in the destruction of atmospheric ozone. It can also undergo photochemical re-emission. Although previous studies indicate possible post-depositional processes, little is known about the diurnal behaviour of these two species and their interaction in surface snow. The mechanisms are still poorly constrained, and no field experiments have been performed in different seasons to investigate the magnitude of re-emission processes Three sampling campaigns conducted at an hourly resolution for 3 d each were carried out near Ny-Ålesund (Svalbard) to study the behaviour of mercury and iodine in surface snow under different sunlight and environmental conditions (24 h darkness, 24 h sunlight and day–night cycles). Our results indicate a different behaviour of mercury and iodine in surface snow during the different campaigns. The day–night experiments demonstrate the existence of a diurnal cycle in surface snow for Hg and iodine, indicating that these species are indeed influenced by the daily solar radiation cycle. Differently, bromine did not show any diurnal cycle. The diurnal cycle also disappeared for Hg and iodine during the 24 h sunlight period and during 24 h darkness experiments supporting the idea of the occurrence (absence) of a continuous recycling or exchange at the snow–air interface. These results demonstrate that this surface snow recycling is seasonally dependent, through sunlight. They also highlight the non-negligible role that snowpack emissions have on ambient air concentrations and potentially on iodine-induced atmospheric nucleation processes.

Diurnal variation in Mars equatorial odd oxygen species: Chemical production and loss mechanisms

D. Viúdez-Moreiras, A. Saiz-Lopez, C.S. Blaszczak-Boxe, J.A. Rodriguez Manfredi, Y. L. Yung

Icarus, Volume 336, 15 January 2020, 113458,, 2019



Odd oxygen (O, O(1D), O3) abundance and its variability in the Martian atmosphere results from complex physical and chemical interactions among atmospheric species, which are driven mainly by solar radiation and atmospheric conditions. Although our knowledge of Mars’ ozone distribution and variability has been significantly improved with the arrival of several recent orbiters, the data acquired by such missions is not enough to properly characterize its diurnal variation. Thus, photochemical models are useful tools to assist in such a characterization. Here, both the Martian ozone vertical distribution and its diurnal variation for equatorial latitudes are studied, using the JPL/Caltech one-dimensional photochemical model and diurnally-variable atmospheric profiles. The chosen equatorial latitude-region is based on the recent and future plans of NASA and other agencies to study this region by different surface missions. A production and loss analysis is performed in order to characterize the chemical mechanisms that drive odd oxygen's diurnal budget and variability on Mars making use of the comprehensive chemistry implemented in the model. The diurnal variation shows large differences in the abundance between daytime and nighttime; and variable behavior depending on the atmospheric layer. The photolysis-driven ozone diurnal profile is obtained at the surface, whilst a sharp decrease is obtained in the upper troposphere at daytime, which originates from the large differences in atomic oxygen abundances between atmospheric layers. Finally, no clear anticorrelation between ozone and water vapor is found in the diurnal cycle, contrary to the strong correlation observed by orbiters on a seasonal timescale.

Experimental Determination of the Photooxidation of Aqueous I− as a Source of Atmospheric I2

Kosuke Watanabe, Shohei Matsuda, Carlos A. Cuevas, Alfonso Saiz-Lopez, Akihiro Yabushita and Yukio Nakano

ACS Earth Space Chem. doi 10.1021/acsearthspacechem.9b00007, 2019



The chemistry of iodine plays an important role in the oxidizing capacity of the global marine atmosphere. In this study, we experimentally determine the photooxidation parameters of iodide ions in aqueous phase (I− (aq)) and estimate the subsequent emission of gaseous iodine molecules (I2(g)) into the atmosphere. The values of the molar absorption coefficient (εiodide(λ)) and the photooxidative quantum yields (Φiodide(λ)) of I− (aq) in the range of 290−500 nm were determined. The influence of pH and dissolved oxygen (DO) on the values of Φiodide(λ) was also investigated. The emission of I2(g) into the atmosphere following the photooxidation of I− (aq) in deionized water solution (pH 5.6, DO 7.8 mg L−1) and artificial seawater solution (pH 8.0, DO 7.0 mg L−1) was estimated to be (2.2 × 10−8 × [I− (aq)]sea) and (1.8 × 10−8 × [I− (aq)]sea) mol L−1 s−1, respectively. Using a global chemistry-climate model, we estimated that the photooxidation of I− (aq) can increase the atmospheric iodine budget by up to ∼8% over some oceanic regions.

Fostering multidisciplinary research on interactions between chemistry, biology, and physics within the coupled cryosphere-atmosphere system

Jennie L. Thomas, Jochen Stutz, Markus M. Frey, Thorsten Bartels-Rausch, Katye Altieri, Foteini Baladima, Jo Browse, Manuel Dall’Osto, Louis Marelle, Jeremie Mouginot, Jennifer G. Murphy, Daiki Nomura, Kerri A. Pratt, Megan D. Willis, Paul Zieger, Jon Abbatt, Thomas A. Douglas, Maria Cristina Facchini, James France‖, Anna E. Jones, Kitae Kim, Patricia A. Matrai, V. Faye McNeill, Alfonso Saiz-Lopez, Paul Shepson, Nadja Steiner, Kathy S. Law, Steve R. Arnold, Bruno Delille, Julia Schmale,  Jeroen E. Sonke,  Aurélien Dommergue, Didier Voisin, Megan L. Melamed and Jessica Gier

Elem Sci Anth, 7(1), p.58,, 2019



The cryosphere, which comprises a large portion of Earth’s surface, is rapidly changing as a consequence of global climate change. Ice, snow, and frozen ground in the polar and alpine regions of the planet are known to directly impact atmospheric composition, which for example is observed in the large influence of ice and snow on polar boundary layer chemistry. Atmospheric inputs to the cryosphere, including aerosols, nutrients, and contaminants, are also changing in the anthropocene thus driving cryosphere-atmosphere feedbacks whose understanding is crucial for understanding future climate. Here, we present the Cryosphere and ATmospheric Chemistry initiative (CATCH) which is focused on developing new multidisciplinary research approaches studying interactions of chemistry, biology, and physics within the coupled cryosphere – atmosphere system and their sensitivity to environmental change. We identify four key science areas: (1) micro-scale processes in snow and ice, (2) the coupled cryosphere-atmosphere system, (3) cryospheric change and feedbacks, and (4) improved decisions and stakeholder engagement. To pursue these goals CATCH will foster an international, multidisciplinary research community, shed light on new research needs, support the acquisition of new knowledge, train the next generation of leading scientists, and establish interactions between the science community and society.

Gas-Phase Photolysis of Hg (I) Radical Species: A New Atmospheric Mercury Reduction Process

Alfonso Saiz-Lopez, A. Ulises Acuña, Tarek Trabelsi, Javier Carmona-García, Juan Z. Dávalos,  Daniel Rivero, Carlos A. Cuevas, Douglas E. Kinnison, Sebastian P. Sitkiewicz, Daniel Roca-Sanjuán, and Joseph S. Francisco

J. Am. Chem. Soc.,, 2019



The efficient gas-phase photoreduction of Hg(II) has recently been shown to change mercury cycling significantly in the atmosphere and its deposition to the Earth’s surface. However, the photolysis of key Hg(I) species within that cycle is currently not considered. Here we present ultraviolet–visible absorption spectra and cross-sections of HgCl, HgBr, HgI, and HgOH radicals, computed by high-level quantum-chemical methods, and show for the first time that gas-phase Hg(I) photoreduction can occur at time scales that eventually would influence the mercury chemistry in the atmosphere. These results provide new fundamental understanding of the photobehavior of Hg(I) radicals and show that the photolysis of HgBr increases atmospheric mercury lifetime, contributing to its global distribution in a significant way.

Holocene atmospheric iodine evolution over the North Atlantic

Juan Pablo Corella, Niccolo Maffezzoli, Carlos Alberto Cuevas, Paul Vallelonga, Andrea Spolaor, Giulio Cozzi, Juliane Müller, Bo Vinther, Carlo Barbante, Helle Astrid Kjær, Ross Edwards, and Alfonso Saiz-Lopez

Clim. Past, 15, 2019–2030,



Atmospheric iodine chemistry has a large influence on the oxidizing capacity and associated radiative impacts in the troposphere. However, information on the evolution of past atmospheric iodine levels is restricted to the industrial period while its long-term natural variability remains unknown. The current levels of iodine in the atmosphere are controlled by anthropogenic ozone deposition to the ocean surface. Here, using high-resolution geochemical measurements from coastal eastern Greenland ReCAP (REnland ice CAP project) ice core, we report the first record of atmospheric iodine variability in the North Atlantic during the Holocene (i.e., the last 11 700 years). Surprisingly, our results reveal that the highest iodine concentrations in the record were found during the Holocene Thermal Maximum (HTM; ∼ 11 500–5500 years before-present). These high iodine levels could be driven by marine primary productivity resulting in an Early Holocene “biological iodine explosion”. The high and stable iodine levels during this past warm period are a useful observational constraint on projections of future changes in Arctic atmospheric composition and climate resulting from global warming.

Impact of halogen chemistry on summertime air quality in coastaland continental Europe: application of the CMAQ model and implications for regulation

Qinyi Li, Rafael Borge, Golam Sarwar, David de la Paz, Brett Gantt, Jessica Domingo, Carlos A. Cuevas, and Alfonso Saiz-Lopez

Atmos. Chem. Phys., 19, 15321–15337,



Halogen (Cl, Br, and I) chemistry has been reported to influence the formation of secondary air pollutants. Previous studies mostly focused on the impact of chlorine species on air quality over large spatial scales. Very little attention has been paid to the effect of the combined halogen chemistry on air quality over Europe and its implications for control policy. In the present study, we apply a widely used regional model, the Community Multiscale Air Quality Modeling System (CMAQ), incorporated with the latest halogen sources and chemistry, to simulate the abundance of halogen species over Europe and to examine the role of halogens in the formation of secondary air pollution. The results suggest that the CMAQ model is able to reproduce the level of O3, NO2, and halogen species over Europe. Chlorine chemistry slightly increases the levels of OH, HO2, NO3, O3, and NO2 and substantially enhances the level of the Cl radical. Combined halogen chemistry induces complex effects on OH (ranging from −0.023 to 0.030 pptv) and HO2 (in the range of −3.7 to 0.73 pptv), significantly reduces the concentrations of NO3 (as much as 20 pptv) and O3 (as much as 10 ppbv), and decreases NO2 in highly polluted regions (as much as 1.7 ppbv); it increases NO2 (up to 0.20 ppbv) in other areas. The maximum effects of halogen chemistry occur over oceanic and coastal regions, but some noticeable impacts also occur over continental Europe. Halogen chemistry affects the number of days exceeding the European Union target threshold for the protection of human beings and vegetation from ambient O3. In light of the significant impact of halogen chemistry on air quality, we recommend that halogen chemistry be considered for inclusion in air quality policy assessments, particularly in coastal cities.

Importance of reactive halogens in the tropical marine atmosphere: a regional modelling study using WRF-Chem

Alba Badia, Claire E. Reeves, Alex R. Baker, Alfonso Saiz-Lopez, Rainer Volkamer, Theodore K. Koenig, Eric C. Apel, Rebecca S. Hornbrook, Lucy J. Carpenter, Stephen J. Andrews, Tomás Sherwen, and Roland von Glasow

Atmos. Chem. Phys., 19, 3161-3189,, 2019



This study investigates the impact of reactive halogen species (RHS, containing chlorine (Cl), bromine (Br) or iodine (I)) on atmospheric chemistry in the tropical troposphere and explores the sensitivity to uncertainties in the fluxes of RHS to the atmosphere and their chemical processing. To do this, the regional chemistry transport model WRF-Chem has been extended to include Br and I, as well as Cl chemistry for the first time, including heterogeneous recycling reactions involving sea-salt aerosol and other particles, reactions of Br and Cl with volatile organic compounds (VOCs), along with oceanic emissions of halocarbons, VOCs and inorganic iodine. The study focuses on the tropical east Pacific using field observations from the Tropical Ocean tRoposphere Exchange of Reactive halogen species and Oxygenated VOC (TORERO) campaign (January–February 2012) to evaluate the model performance.

Including all the new processes, the model does a reasonable job reproducing the observed mixing ratios of bromine oxide (BrO) and iodine oxide (IO), albeit with some discrepancies, some of which can be attributed to difficulties in the model's ability to reproduce the observed halocarbons. This is somewhat expected given the large uncertainties in the air–sea fluxes of the halocarbons in a region where there are few observations of their seawater concentrations.

We see a considerable impact on the inorganic bromine (Bry) partitioning when heterogeneous chemistry is included, with a greater proportion of the Bry in active forms such as BrO, HOBr and dihalogens. Including debromination of sea salt increases BrO slightly throughout the free troposphere, but in the tropical marine boundary layer, where the sea-salt particles are plentiful and relatively acidic, debromination leads to overestimation of the observed BrO. However, it should be noted that the modelled BrO was extremely sensitive to the inclusion of reactions between Br and the oxygenated VOCs (OVOCs), which convert Br to HBr, a far less reactive form of Bry. Excluding these reactions leads to modelled BrO mixing ratios greater than observed. The reactions between Br and aldehydes were found to be particularly important, despite the model underestimating the amount of aldehydes observed in the atmosphere. There are only small changes to the inorganic iodine (Iy) partitioning and IO when the heterogeneous reactions, primarily on sea salt, are included.

Our model results show that tropospheric Ox loss due to halogens ranges between 25 % and 60 %. Uncertainties in the heterogeneous chemistry accounted for a small proportion of this range (25 % to 31 %). This range is in good agreement with other estimates from state-of-the-art atmospheric chemistry models. The upper bound is found when reactions between Br and Cl with VOCs are not included and, consequently, Ox loss by BrOx, ClOx and IOx cycles is high (60 %). With the inclusion of halogens in the troposphere, O3 is reduced by 7 ppbv on average. However, when reactions between Br and Cl with VOCs are not included, O3 is much lower than observed. Therefore, the tropospheric Ox budget is highly sensitive to the inclusion of halogen reactions with VOCs and to the uncertainties in current understanding of these reactions and the abundance of VOCs in the remote marine atmosphere.

Influence of bromine and iodine chemistry on annual, seasonal, diurnal, and background ozone: CMAQ simulations over the Northern Hemisphere

Golam Sarwara, Brett Ganttb, Kristen Foleya, Kathleen Faheya, Tanya L. Speroa, Daiwen Kanga, Rohit Mathura, Hosein Foroutanc, Jia Xingd, Tomás Sherwene,f, Alfonso Saiz-Lopez

Atmospheric Environment, Volume 213, 15 September 2019, Pages 395-404,




Bromine and iodine chemistry has been updated in the Community Multiscale Air Quality (CMAQ) model to better capture the influence of natural emissions from the oceans on ozone concentrations. Annual simulations were performed using the hemispheric CMAQ model without and with bromine and iodine chemistry. Model results over the Northern Hemisphere show that including bromine and iodine chemistry in CMAQ not only reduces ozone concentrations within the marine boundary layer but also aloft and inland. Bromine and iodine chemistry reduces annual mean surface ozone over seawater by 25%, with lesser ozone reductions over land. The bromine and iodine chemistry decreases ozone concentration without changing the diurnal profile and is active throughout the year. However, it does not have a strong seasonal influence on ozone over the Northern Hemisphere. Model performance of CMAQ is improved by the bromine and iodine chemistry when compared to observations, especially at coastal sites and over seawater. Relative to bromine, iodine chemistry is approximately four times more effective in reducing ozone over seawater over the Northern Hemisphere (on an annual basis). Model results suggest that the chemistry modulates intercontinental transport and lowers the background ozone imported to the United States.

Is a scaling factor required to obtain closure between measured and modelled atmospheric O4 absorptions? An assessment of uncertainties of measurements and radiative transfer simulations for 2 selected days during the MAD-CAT campaign

Thomas Wagner, Steffen Beirle, Nuria Benavent , Tim Bösch, Ka Lok Chan, Sebastian Donner, Steffen Dörner, Caroline Fayt, Udo Frieß, David García-Nieto, Clio Gielen, David González-Bartolome, Laura Gomez, François Hendrick, Bas Henzing, Jun Li Jin, Johannes Lampel, Jianzhong Ma, Kornelia Mies, Mónica Navarro, Enno Peters, Gaia Pinardi, Olga Puentedura, Janis Puķīte, Julia Remmers, Andreas Richter, Alfonso Saiz-Lopez, Reza Shaiganfar, Holger Sihler, Michel Van Roozendael, Yang Wang, and Margarita Yela

Atmos. Meas. Tech., 12, 2745-2817, 2019,, 2019




In this study the consistency between MAX-DOAS measurements and radiative transfer simulations of the atmospheric O4 absorption is investigated on 2 mainly cloud-free days during the MAD-CAT campaign in Mainz, Germany, in summer 2013. In recent years several studies indicated that measurements and radiative transfer simulations of the atmospheric O4 absorption can only be brought into agreement if a so-called scaling factor (<1) is applied to the measured O4 absorption. However, many studies, including those based on direct sunlight measurements, came to the opposite conclusion, that there is no need for a scaling factor. Up to now, there is no broad consensus for an explanation of the observed discrepancies between measurements and simulations. Previous studies inferred the need for a scaling factor from the comparison of the aerosol optical depths derived from MAX-DOAS O4 measurements with that derived from coincident sun photometer measurements. In this study a different approach is chosen: the measured O4 absorption at 360 nm is directly compared to the O4 absorption obtained from radiative transfer simulations. The atmospheric conditions used as input for the radiative transfer simulations were taken from independent data sets, in particular from sun photometer and ceilometer measurements at the measurement site. This study has three main goals: first all relevant error sources of the spectral analysis, the radiative transfer simulations and the extraction of the input parameters used for the radiative transfer simulations are quantified. One important result obtained from the analysis of synthetic spectra is that the O4 absorptions derived from the spectral analysis agree within 1 % with the corresponding radiative transfer simulations at 360 nm. Based on the results from sensitivity studies, recommendations for optimised settings for the spectral analysis and radiative transfer simulations are given. Second, the measured and simulated results are compared for 2 selected cloud-free days with similar aerosol optical depths but very different aerosol properties. On 18 June, measurements and simulations agree within their (rather large) uncertainties (the ratio of simulated and measured O4 absorptions is found to be 1.01±0.16). In contrast, on 8 July measurements and simulations significantly disagree: for the middle period of that day the ratio of simulated and measured O4 absorptions is found to be 0.82±0.10, which differs significantly from unity. Thus, for that day a scaling factor is needed to bring measurements and simulations into agreement. Third, recommendations for further intercomparison exercises are derived. One important recommendation for future studies is that aerosol profile data should be measured at the same wavelengths as the MAX-DOAS measurements. Also, the altitude range without profile information close to the ground should be minimised and detailed information on the aerosol optical and/or microphysical properties should be collected and used.

The results for both days are inconsistent, and no explanation for a O4 scaling factor could be derived in this study. Thus, similar but more extended future studies should be performed, including more measurement days and more instruments. Also, additional wavelengths should be included.

MAX-DOAS measurements and vertical profiles of glyoxal and formaldehyde in Madrid, Spain

Nuria Benavent, David Garcia-Nieto, Shanshan Wang, Alfonso Saiz-Lopez

Atmospheric Environment, Volume 199, 15 February 2019, Pages 357-367,



Glyoxal (CHOCHO) and formaldehyde (HCHO) are organic trace gases that play an important role in tropospheric chemistry as oxidation products of a number of volatile organic compounds (VOCs). In this study, we report year-round daytime measurements of glyoxal and formaldehyde in the urban atmosphere of Madrid, Spain. Their vertical concentration profiles were retrieved using the Multi AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) technique and a Radiative Transfer Model (RTM) that simulates solar photon paths through the atmosphere. The diurnal variations of HCHO show two distinct peaks during the day, in the early morning and late afternoon in spring and summer, while the second peak is shifted towards noon in autumn and winter, due to lower photolysis rates and more effective boundary layer accumulation of HCHO in those seasons. The HCHO surface mixing ratios range from 6 ppbv to 27 ppbv in spring-summer and from 10 ppbv to 30 ppbv in autumn-winter. Monthly hourly-averaged glyoxal surface mixing ratios in the early morning show higher values during winter, 2 ppbv, than in summer, 0.7 ppbv. We also evaluated the ratio between glyoxal and formaldehyde (RGF) surface mixing ratios, as an indicator of the nature of VOCs precursors. The RGF was also correlated with the measured NO2, which represents a direct signal of anthropogenic emissions, along with the VOCs emission inventories in Madrid. The RGF results yielded higher ratios in spring, 0.1–0.13, than in winter and autumn (in the range of 0.02–0.07) when NO2 levels were higher.

Modeling the Sources and Chemistry of Polar Tropospheric Halogens (Cl, Br, and I) Using the CAM‐Chem Global Chemistry‐Climate Model

Rafael P. Fernandez, Antía Carmona‐Balea, Carlos A. Cuevas, Javier A. Barrera, Douglas E. Kinnison, Jean‐Francois Lamarque, Christopher Blaszczak‐Boxe, Kitae Kim, Wonyong Choi, Timothy Hay, Anne‐Marlene Blechschmidt, Anja Schönhardt, John P. Burrows, Alfonso Saiz‐Lopez

Journal of Advances in Modeling Earth Syatems, Volume 11, Issue 7, August 2019, Pages 2259-2289,



Current chemistry climate models do not include polar emissions and chemistry of halogens. This work presents the first implementation of an interactive polar module into the very short‐lived (VSL) halogen version of the Community Atmosphere Model with Chemistry (CAM‐Chem) model. The polar module includes photochemical release of molecular bromine, chlorine, and interhalogens from the sea‐ice surface, and brine diffusion of iodine biologically produced underneath and within porous sea‐ice. It also includes heterogeneous recycling of inorganic halogen reservoirs deposited over fresh sea‐ice surfaces and snow‐covered regions. The polar emission of chlorine, bromine, and iodine reach approximately 32, 250, and 39 Gg/year for Antarctica and 33, 271, and 4 Gg/year for the Arctic, respectively, with a marked seasonal cycle mainly driven by sunlight and sea‐ice coverage. Model results are validated against polar boundary layer measurements of ClO, BrO, and IO, and satellite BrO and IO columns. This validation includes satellite observations of IO over inner Antarctica for which an iodine “leapfrog” mechanism is proposed to transport active iodine from coastal source regions to the interior of the continent. The modeled chlorine and bromine polar sources represent up to 45% and 80% of the global biogenic VSLCl and VSLBr emissions, respectively, while the Antarctic sea‐ice iodine flux is ~10 times larger than that from the Southern Ocean. We present the first estimate of the contribution of polar halogen emissions to the global tropospheric halogen budget. CAM‐Chem includes now a complete representation of halogen sources and chemistry from pole‐to‐pole and from the Earth's surface up to the stratopause.

Nitrite-Induced Activation of Iodate into Molecular Iodine in Frozen Solution

Kitae Kim, Jinjung Ju, Bomi Kim, Hyun Young Chung, L’ubica Vetráková, Dominik Heger, Alfonso Saiz-Lopez, Wonyong Choi and Jungwon Kim

Environ. Sci. Technol.DOI:10.1021/acs.est.8b06638, 2019



A new mechanism for the abiotic production of moleculariodine (I2) from iodate (IO3−), which is the most abundant iodine species,in dark conditions was identified and investigated. The production of I2inaqueous solution containing IO3−and nitrite (NO2−)at25°C wasnegligible. However, the redox chemical reaction between IO3−and NO2−rapidly proceeded in frozen solution at−20°C, which resulted in theproduction of I2,I−, and NO3−. The rapid redox chemical reactionbetween IO3−and NO2−in frozen solution is ascribed to the accumulationof IO3−,NO2−, and protons in the liquid regions between ice crystalsduring freezing (freeze concentration effect). This freeze concentrationeffect was verified by confocal Raman microscopy for the soluteconcentration and UV−visible absorption spectroscopy with cresol red(acid−base indicator) for the proton concentration. The freezing-inducedproduction of I2in the presence of IO3−and NO2−was observed undervarious conditions, which suggests this abiotic process for I2production is not restricted to a specific region and occurs in manycold regions. NO2−-induced activation of IO3−to I2in frozen solution may help explain why the measured values of iodine arelarger than the modeled values in some polar areas

Novel approaches to improve estimates of short-lived halocarbonemissions during summer from the Southern Oceanusing airborne observations

Elizabeth Asher, Rebecca S. Hornbrook, Britton B. Stephens, Doug Kinnison, Eric J. Morgan, Ralph F. Keeling,Elliot L. Atlas, Sue M. Schauffler, Simone Tilmes, Eric A. Kort, Martin S. Hoecker-Martínez, Matt C. Long, Jean-François Lamarque, Alfonso Saiz-Lopez, Kathryn McKain, Colm Sweeney, Alan J. Hills, and Eric C. Apel

Atmos. Chem. Phys., 19, 14071–14090,



Fluxes of halogenated volatile organic compounds(VOCs) over the Southern Ocean remain poorly understood,and few atmospheric measurements exist to constrain mod-eled emissions of these compounds. We present observa-tions of CHBr3, CH2Br2, CH3I, CHClBr2, CHBrCl2, andCH3Br during the O2/N2Ratio and CO2Airborne SouthernOcean (ORCAS) study and the second Atmospheric Tomog-raphy mission (ATom-2) in January and February of 2016and 2017. Good model–measurement correlations were ob-tained between these observations and simulations from theCommunity Earth System Model (CESM) atmospheric com-ponent with chemistry (CAM-Chem) for CHBr3, CH2Br2,CH3I, and CHClBr2but all showed significant differences inmodel : measurement ratios. The model : measurement com-parison for CH3Br was satisfactory and for CHBrCl2the lowlevels present precluded us from making a complete assess-ment. Thereafter, we demonstrate two novel approaches toestimate halogenated VOC fluxes; the first approach takesadvantage of the robust relationships that were found be-tween airborne observations of O2and CHBr3, CH2Br2,and CHClBr2. We use these linear regressions with O2andmodeled O2distributions to infer a biological flux of halo-genated VOCs. The second approach uses the StochasticTime-Inverted Lagrangian Transport (STILT) particle disper-sion model to explore the relationships between observedmixing ratios and the product of the upstream surface influ-ence of sea ice, chla, absorption due to detritus, and down-ward shortwave radiation at the surface, which in turn re-late to various regional hypothesized sources of halogenatedVOCs such as marine phytoplankton, phytoplankton in sea-ice brines, and decomposing organic matter in surface sea-water. These relationships can help evaluate the likelihood ofparticular halogenated VOC sources and in the case of statis-tically significant correlations, such as was found for CH3I,may be used to derive an estimated flux field. Our resultsare consistent with a biogenic regional source of CHBr3andboth nonbiological and biological sources of CH3I over theseregions.

Observations of iodine oxide in the Indian Ocean marine boundary layer: A transect from the tropics to the high latitudes

Anoop S. Mahajan, Liselotte Tinel, Shrivardhan Hulswar, Carlos A. Cuevas, Shanshan Wang, Sachin Ghude, Ravidas K. Naike, Rajani K. Mishra, P. Sabu, Amit Sarkar, N. Anilkumar, Alfonso Saiz-Lopez

Atmospheric Environment: X, Volume 1, January 2019, 100016,, 2019.




Observations of iodine oxide (IO) were made in the Indian Ocean and the Southern Ocean marine boundary layer (MBL) during the 8th Indian Southern Ocean Expedition. IO was observed almost ubiquitously in the open ocean with larger mixing ratios south of the Polar Front (PF). Contrary to previous reports, IO was not positively correlated to sea surface temperature (SST)/salinity, or negatively to chlorophyll a. Over the whole expedition, SST showed a weak negative correlation with respect to IO while chl a was positively correlated. North of the PF, chl a showed a strong positive correlation with IO. The computed HOI and I2 fluxes do not show any significant correlation with atmospheric IO. Simulations with the global CAM-Chem model show a reasonably good agreement with observations north of the PF but the model fails to reproduce the elevated IO south of the PF indicating that the current emission parametrizations are not sufficient to explain iodine chemistry in the Southern Indian Ocean.

Ocean Biogeochemistry Control on the Marine Emissionsof Brominated Very Short‐Lived Ozone‐DepletingSubstances: A Machine‐Learning Approach

Siyuan Wang, Douglas Kinnison, Stephen A. Montzka, Eric C. Apel, Rebecca S. Hornbrook , Alan J. Hills, Donald R. Blake, Barbara Barletta, Simone Meinardi, Colm Sweeney, Fred Moore, Matthew Long, Alfonso Saiz‐Lopez, Rafael Pedro Fernandez, Simone Tilmes, Louisa K. Emmons, and Jean‐François Lamarque

Journal of Geophysical Research: Atmospheres,124.



Halogenated very short lived substances (VSLS) affect the ozone budget in the atmosphere.Brominated VSLS are naturally emitted from the ocean, and current oceanic emission inventories varydramatically. We present a new global oceanic emission inventory of Br‐VSLS (bromoform anddibromomethane), considering the physical forcing in the ocean and the atmosphere, as well as the oceanbiogeochemistry control. A data‐oriented machine‐learning emulator was developed to couple the air‐seaexchange with the ocean biogeochemistry. The predicted surface seawater concentrations and the surfaceatmospheric mixing ratios of Br‐VSLS are evaluated with long‐term, global‐scale observations; and thepredicted vertical distributions of Br‐VSLS are compared to the global airborne observations in both borealsummer and winter. The global marine emissions of bromoform and dibromomethane are estimatedto be 385 and 54 Gg Br per year, respectively. The new oceanic emission inventory of Br‐VSLS is more skillfulthan the widely used top‐down approaches for representing the seasonal/spatial variations and theannual means of atmospheric concentrations. The new approach improves the model predictability for thecoupled Earth system model and can be used as a basis for investigating the past and future ocean emissionsand feedbacks under climate change. This model framework can be used to calculate the bidirectionaloceanicfluxes for other compounds of interest.

Recent increase in NO2 levels in the southeast of the Iberian Peninsula

J.A. Adame a, A. Notario, C.A. Cuevas , A. Lozano , M. Yela, A. Saiz-Lopez

Science of The Total Environment, Volume 693, 25 November 2019, 133587,



We report the evolution of tropospheric NO2 over the south-east of the Iberian Peninsula from 2005 to 2017. We have used hourly NO2 levels measured at air-quality stations in urban and suburban environments. Annual averages ranged between 14 and 45 μg m−3, with peaks above 200 μg m−3. A monthly variation was observed, with higher concentrations in cold months (40–60 μg m−3) and lower levels in the warm season (13–17 μg m−3). A diurnal pattern was found in urban and suburban areas. The upward trend in NO2 observed during the whole period contrasts with the upward trend reported in 2013–2017. The NO2 tropospheric column levels measured by the Ozone Monitoring Instrument over the Iberian Peninsula indicated a similar behaviour; nevertheless, the largest Spanish metropolitan areas did not show this increase. The mean sea level pressure and wind field data of ERA5 (European Centre for Medium-Range Weather Forecasts) were used to investigate the weather conditions, the NO2 outputs of the Copernicus Monitoring Services being used for the assessment of the NO2 spatial distribution. NO2 regional events, with concentrations in the range 140–150 μg m−3, and which occurred both in the winter and summer season under anticyclonic conditions, are also described. A local origin is identified in winter, whereas in summer, they are associated with a high-pressure system that blocks Mediterranean outflows towards the Atlantic Ocean. The high NO2 levels are attributed mainly to two factors: i) local emissions, rather than contributions from the western Mediterranean (or even North Africa), and ii) an increase in the pressure gradient between the Atlantic and the Mediterranean pressure systems, associated with a decrease in wind speed, was found during the last five years compared with the previous eight. Meteorological and chemical changes in mid-latitudes associated with global warming should also be investigated in the future.

Simultaneous and Synergic Production of Bioavailable Iron andReactive Iodine Species in Ice.

Kitae Kim, Sunil Paul M. Menacherry, Jungwon Kim, Hyun Young Chung, Daun Jeong, Alfonso Saiz-Lopez, Wonyong Choi

Environ. Sci. Technol. 2019,, 2019



The bioavailable iron is essential for all living organisms, and the dissolution of iron oxide contained in dust and soil is one of the major sources of bioavailable iron in nature. Iodine in the polar atmosphere is related to ozone depletion, mercury oxidation, and cloud condensation nuclei formation. Here we show that the chemical reaction between iron oxides and iodide (I–) is markedly accelerated to produce bioavailable iron (Fe(II)aq) and tri-iodide (I3–: evaporable in the form of I2) in frozen solution (both with and without light irradiation), while it is negligible in aqueous phase. The freeze-enhanced production of Fe(II)aq and tri-iodide is ascribed to the freeze concentration of iron oxides, iodides, and protons in the ice grain boundaries. The outdoor experiments carried out in midlatitude during a winter day (Pohang, Korea: 36°0′ N, 129°19′ E) and in an Antarctic environment (King George Island: 62°13′ S 58°47′ W) also showed the enhanced generation of Fe(II)aq and tri-iodide in ice. This study proposes a previously unknown abiotic mechanism and source of bioavailable iron and active iodine species in the polar environment. The pulse input of bioavailable iron and reactive iodine when ice melts may influence the oceanic primary production and CCN formation.

TEMPO Green Paper: Chemistry, physics, and meteorology experiments with the Tropospheric Emissions: monitoring of pollution instrument

K. Chance, X. Liu, C. Chan Miller, G. González Abad, G. Huang, C. Nowlan, A. Souri, R. Suleiman, K. Sun, H. Wang, L. Zhu, P. Zoogman, J. Al-Saadi, J. - C. Antuña-Marrero, J. Carr, R. Chatfield, M. Chin, R. Cohen, D. Edwards, J. Fishman, D. Flittner, J. Geddes, M. Grutter, J. R. Herman, D. J. Jacob, S. Janz, J. Joiner, J. Kim, N. A. Krotkov, B. Lefer, R. V. Martin, O. L. Mayol-Bracero, A. Naeger, M. Newchurch, G. G. Pfister, K. Pickering, R. B. Pierce, C. Rivera Cárdenas, A. Saiz-Lopez, W. Simpson, E. Spinei, R. J. D. Spurr, J. J. Szykman, O. Torres, J. Wang

Proc. SPIE 11151, Sensors, Systems, and Next-Generation Satellites XXIII, 111510B (10 October 2019); doi: 10.1117/12.2534883



The NASA/Smithsonian Tropospheric Emissions: Monitoring of Pollution (TEMPO; satellite instrument will measure atmospheric pollution and much more over Greater North America at high temporal resolution (hourly or better in daylight, with selected observations at 10 minute or better sampling) and high spatial resolution (10 km2 at the center of the field of regard). It will measure ozone (O3) profiles (including boundary layer O3), and columns of nitrogen dioxide (NO2), nitrous acid (HNO2), sulfur dioxide (SO2), formaldehyde (H2CO), glyoxal (C2H2O2), water vapor (H2O), bromine oxide (BrO), iodine oxide (IO), chlorine dioxide (OClO), as well as clouds and aerosols, foliage properties, and ultraviolet B (UVB) radiation. The instrument has been delivered and is awaiting spacecraft integration and launch in 2022. This talk describes a selection of TEMPO applications based on the TEMPO Green Paper living document ( Applications to air quality and health will be summarized. Other applications presented include: biomass burning and O3 production; aerosol products including synergy with GOES infrared measurements; lightning NOx; soil NOx and fertilizer application; crop and forest damage from O3; chlorophyll and primary productivity; foliage studies; halogens in coastal and lake regions; ship tracks and drilling platform plumes; water vapor studies including atmospheric rivers, hurricanes, and corn sweat; volcanic emissions; air pollution and economic evolution; high-resolution pollution versus traffic patterns; tidal effects on estuarine circulation and outflow plumes; air quality response to power blackouts and other exceptional events.

Organic bromine compounds produced in sea ice in Antarctic winter

Katarina Abrahamsson, Anna Granfors, Martin Ahnoff, Carlos A. Cuevas, Alfonso Saiz-Lopez

Nature Communications volume 9, Article number: 5291, 2018.



During polar springtime, active bromine drives ozone, a greenhouse gas, to near-zero levels. Bromine production and emission in the polar regions have so far been assumed to require sunlight. Here, we report measurements of bromocarbons in sea ice, snow, and air during the Antarctic winter that reveal an unexpected new source of organic bromine to the atmosphere during periods of no sunlight. The results show that Antarctic winter sea ice provides 10 times more bromocarbons to the atmosphere than Southern Ocean waters, and substantially more than summer sea ice. The inclusion of these measurements in a global climate model indicates that the emitted bromocarbons will disperse throughout the troposphere in the southern hemisphere and through photochemical degradation to bromine atoms, contribute ~ 10% to the tropospheric reactive bromine budget. Combined together, our results suggest that winter sea ice could potentially be an important source of atmospheric bromine with implications for atmospheric chemistry and climate at a hemispheric scale.

Vertical and horizontal distribution of regional new particle formation events in Madrid

Cristina Carnerero, Noemí Pérez, Cristina Reche, Marina Ealo, Gloria Titos, Hong-Ku Lee, Hee-Ram Eun, Yong-Hee Park, Lubna Dada, Pauli Paasonen, Veli-Matti Kerminen, Enrique Mantilla, Miguel Escudero, Francisco J. Gómez-Moreno, Elisabeth Alonso-Blanco, Esther Coz, Alfonso Saiz-Lopez, Brice Temime-Roussel, Nicolas Marchand, David C. S. Beddows, Roy M. Harrison, Tuukka Petäjä, Markku Kulmala, Kang-Ho Ahn, Andrés Alastuey, and Xavier Querol

Atmos. Chem. Phys., 18, 16601–16618, 2018,



The vertical profile of new particle formation (NPF) events was studied by comparing the aerosol size number distributions measured aloft and at surface level in a suburban environment in Madrid, Spain, using airborne instruments. The horizontal distribution and regional impact of the NPF events was investigated with data from three ur- ban, urban background, and suburban stations in the Madrid metropolitan area. Intensive regional NPF episodes followed by particle growth were simultaneously recorded at three stations in and around Madrid during a field campaign in July 2016. The urban stations presented larger formation rates compared to the suburban station. Condensation and coag- ulation sinks followed a similar evolution at all stations, with higher values at urban stations. However, the total number concentration of particles larger than 2.5 nm was lower at the urban station and peaked around noon, when black carbon (BC) levels are at a minimum. The vertical soundings demon- strated that ultrafine particles (UFPs) are formed exclusively inside the mixed layer. As convection becomes more effective and the mixed layer grows, UFPs are detected at higher levels. The morning soundings revealed the presence of a residual layer in the upper levels in which aged particles (nucleated and grown on previous days) prevail. The particles in this layer also grow in size, with growth rates sig- nificantly smaller than those inside the mixed layer. Under conditions with strong enough convection, the soundings re- vealed homogeneous number size distributions and growth rates at all altitudes, which follow the same evolution at the other stations considered in this study. This indicates that UFPs are detected quasi-homogenously in an area spanning at least 17 km horizontally. The NPF events extend over the full vertical extension of the mixed layer, which can reach as high as 3000 m in the area, according to previous studies. On some days a marked decline in particle size (shrinkage) was observed in the afternoon, associated with a change in air masses. Additionally, a few nocturnal nucleation-mode bursts were observed at the urban stations, for which further research is needed to elucidate their origin.

Photoreduction of gaseous oxidized mercury changes global atmospheric mercury speciation, transport and deposition

Alfonso Saiz-Lopez, Sebastian P. Sitkiewicz, Daniel Roca-Sanjuán, Josep M. Oliva-Enrich, Juan Z. Dávalos, Rafael Notario, Martin Jiskra, Yang Xu, Feiyue Wang, Colin P. Thackray, Elsie M. Sunderland, Daniel J. Jacob, Oleg Travnikov, Carlos A. Cuevas, A. Ulises Acuña, Daniel Rivero, John M.C. Plane, Douglas E. Kinnison & Jeroen E. Sonke

Nature Communications (2018) 9:4796, doi: 10.1038/s41467-018-07075-3



Anthropogenic mercury (Hg(0)) emissions oxidize to gaseous Hg(II) compounds, before deposition to Earth surface ecosystems. Atmospheric reduction of Hg(II) competes with deposition, thereby modifying the magnitude and pattern of Hg deposition. Global Hg models have postulated that Hg(II) reduction in the atmosphere occurs through aqueous-phase photoreduction that may take place in clouds. Here we report that experimental rainfall Hg(II) photoreduction rates are much slower than modelled rates. We compute absorption cross sections of Hg(II) compounds and show that fast gas-phase Hg(II) photolysis can dominate atmospheric mercury reduction and lead to a substantial increase in the modelled, global atmospheric Hg lifetime by a factor two. Models with Hg(II) photolysis show enhanced Hg(0) deposition to land, which may prolong recovery of aquatic ecosystems long after Hg emissions are lowered, due to the longer residence time of Hg in soils compared with the ocean. Fast Hg(II) photolysis substantially changes atmospheric Hg dynamics and requires further assessment at regional and local scales.

Abiotic and biotic sources influencing spring new particle formation in North East Greenland

M. Dall´Ostoa, R. Simo, Roy M. Harrison, D.C.S. Beddows, A. Saiz-Lopez, R. Lang, H. Skov, J.K. Nøjgaard, I.E. Nielsen, A. Massling

Atmospheric Environment, Volume 190, October 2018, Pages 126-134,



In order to improve our ability to predict cloud properties, radiative balance and climate, it is crucial to understand the mechanisms that trigger the formation of new particles and their growth to activation sizes. Using an array of real time aerosol measurements, we report a categorization of the aerosol population taken at Villum Research Station, Station Nord (VRS) in North Greenland during a period of 88 days (February–May 2015). A number of New Particle Formation (NPF) events were detected and are herein discussed. Air mass back trajectories analysis plotted over snow-sea ice satellite maps allowed us to correlate early spring (April) NPF events with air masses travelling mainly over snow on land and sea ice, whereas late spring (May) NPF events were associated with air masses that have passed mainly over sea ice regions. Concomitant aerosol mass spectrometry analysis suggests methanesulfonic acid (MSA) and molecular iodine (I2) may be involved in the NPF mechanisms. The source of MSA was attributed to open leads within the sea ice. By contrast, iodine was associated with air masses over snow on land and over sea ice, suggesting both abiotic and biotic sources. Measurements of nucleating particle composition as well as gas-phase species are needed to improve our understanding of the links between emissions, aerosols, cloud and climate in the Arctic; therefore our ability to model such processes.

Nitrate photolysis in ice and snow: A critical review of its multiphase chemistry.

Christopher S. Blaszczak-Boxe, Alfonso Saiz-Lopez

Atmospheric Environment, Volume 193, November 2018, Pages 224-241,



Nitrate, a member of the oxidized nitrogen family (NOy), is one of the primary species involved in the nitrogen cycle and thus plays a key role in ecosystem processes, globally. It exists as nitrate salts and as nitric acid (HNO3) in both aerosols and the gas phase. It is formed from the NO3 radical/N2O5 or directly from the oxidation of NO2 and is lost by photolysis, OH oxidation, and deposition. In regions covered with snow/ice it has a significant impact on air quality, atmospheric oxidizing capacity, greenhouse gas concentrations, and paleoclimate/isotopic data. Snow/ice environments can, at seasonal maximum, comprise ∼30% of Earth's surface area while 10% is covered with ice/snow found at the polar cryosphere. Nitrate makes up 75–100% of the nitrogen budget deposited from the atmosphere and measured at the Arctic and Antarctica. Its concentrations in Greenland ice have risen by a factor of 2–3, reflecting the long-ranged transport of increased anthropogenic NOx (NO + NO2) emissions.

The polar cryosphere is an active medium for the movement of traces gases, such as nitrate, between the snowpack/sea-ice and overlying atmosphere. Field, laboratory, and modeling efforts have quantitatively shown that the exchange of trace species between the snowpack and the air above is governed by photochemistry in combination with air moving gases between these two matrices. Polar tropospheric chemistry and dynamics immensely impact processes governing chemical composition, isotopic signatures, oxidizing capacity, and thus regional climate. This study presents a comprehensive review of laboratory and modeling efforts – contextualized by field measurements – that have elucidated physicochemical processes governing nitrate photochemistry and its impact on the polar snowpack. Specifically, after an Introduction to nitrate photochemistry in ice, we discuss the: 1) initial Arctic field measurements that sparked interest in ice photolysis in the polar regions; 2) suite of follow-up field studies that catalyzed laboratory and snow-chamber investigations that gave deeper understanding of the effects of snow/ice – air trace gas exchange due to nitrate photochemistry; 3) complementary laboratory, snow-chamber investigations; and 4) a detailed review of recent nitrate ice photolysis laboratory experiments and the potential impact of utilizing laboratory and computational models to study the role of nitrate in the nitrogen cycle.

Single-Molecule Catalysis Revealed: Elucidating the Mechanistic Framework for the Formation and Growth of Atmospheric Iodine Oxide Aerosols in Gas-Phase and Aqueous Surface Environments

Manoj Kumar, Alfonso Saiz-Lopez, and Joseph S. Francisco

J. Am. Chem. Soc., 2018, 140 (44), pp 14704–14716, https://doi: 10.1021/jacs.8b07441



Iodine oxide aerosols are ubiquitous in many coastal atmospheric environments. However, the exact mechanism responsible for their homogeneous nucleation and subsequent cluster growth remains to be fully established. Using quantum chemical calculations, we propose a new mechanistic framework for the formation and subsequent growth of iodine oxide aerosols, which takes advantage of noncovalent interactions between iodine oxides (I2O5 and I2O4) and iodine acids (HIO3 and HIO2). Larger iodine oxide clusters are suggested to be formed in a facile manner and with enhanced exothermicity. The newly proposed mechanisms follow both concerted and stepwise pathways. In all these new chemistries, an O:I ratio of 2–2.5 is predicted, which satisfies an experimentally derived criterion recently proposed for identifying iodine oxides involved in atmospheric aerosol formation. Born–Oppenheimer molecular dynamics simulations at the air–water interface suggest that I2O5 and I4O10, which are two of the most common nucleating iodine oxides, react with interfacial water on the picosecond time scale and result in novel nucleating species such as H2I2O6 and HI4O11– or I3O8. An important implication of these simulation results is that aqueous surfaces, which are ubiquitous in the atmosphere, may activate iodine oxides to result in a new class of nucleating compounds, which can form mixed aerosol particles with potent precursors, such as HIO3 or H2SO4, in marine air masses via typical acid-based interactions. Overall, these results give a better understanding of iodine-rich aerosols in diverse environments.

The Role of Climate: 71 ka of Atmospheric Mercury Deposition in the Southern Hemisphere Recorded by Rano Aroi Mire, Easter Island (Chile)

Marta Pérez-Rodríguez, Olga Margalef, Juan Pablo Corella, Alfonso Saiz-Lopez, Sergi Pla-Rabes, Santiago Giralt and Antonio Martínez Cortizas

Geosciences 2018, 8(10), 374;



The study of mercury accumulation in peat cores provides an excellent opportunity to improve the knowledge on mercury cycling and depositional processes at remote locations far from pollution sources. We analyzed mercury concentrations in 150 peat samples from two cores from Rano Aroi (Easter Island, 27° S) and in selected vegetation samples of present-day flora of the island, in order to characterize the mercury cycling for the last ~71 ka BP. The mercury concentrations showed values ranging between 35 and 200 ng g−1, except for a large maxima (~1000 ng g−1) which occurred at the end of the Last Glacial Maximum (LGM, ~20 ka cal BP) in both peat cores. Low temperatures during the LGM would accelerate the atmospheric oxidation of Hg(0) to divalent mercury that, coupled with higher rainfall during this period, most likely resulted in a very efficient surface deposition of atmospheric mercury. Two exceptional short-lived Hg peaks occurred during the Holocene at 8.5 (350 ng g−1) and 4.7 (1000 ng g−1) ka cal BP. These values are higher than those recorded in most peat records belonging to the industrial period, highlighting that natural factors played a significant role in Hg accumulation—sometimes even more so than anthropogenic sources. Our results suggest that wet deposition, linked to atmospheric oxidation, was the main process controlling the short-lived Hg events, both in the mire and in the catchment soils.

Study of the exceptional meteorological conditions, trace gases and particulate matter measured during the 2017 forest fire in Doñana Natural Park, Spain

J.A. Adame, L. Lope, P.J. Hidalgo, M. Sorribas, I. Gutiérrez-Álvarez, A.del Águila, A. Saiz-Lopez, M.Yela

Science of The Total Environment, Volume 645, 15 December 2018, Pages 710-720,



In late June 2017, a forest fire occurred in Doñana Natural Park, which is located in southwestern Europe. Many animal and plant species, some of which are threatened, suffered from the impact of this fire, and important ecosystems in the European Union were seriously affected. This forest fire occurred under exceptional weather conditions. The meteorological situation was studied at both the synoptic scale and the local scale using meteorological fields in the ERA-Interim global model from ECMWF (European Centre for Medium Range Weather Forecasts), the WRF (Weather Research and Forecasting) mesoscale model and ground observations collected at El Arenosillo observatory. Anomalies were obtained using records (observations and simulations) over the last two decades (1996–2016). An anticyclonic system dominated the synoptic meteorological conditions, but a strong pressure gradient was present; positive high pressure anomalies and negative low pressure anomalies resulted in intense NW flows. At the surface, wind gusts of 80 km h−1, temperatures up to 35 °C and relative humidity values <20% were observed. In terms of anomalies, these observations corresponded to positive temperature anomalies (differences of 12 °C), positive wind speed anomalies (>29 km h−1) and negative relative humidity anomalies (differences of 40%). The forest fire reached El Arenosillo observatory approximately 8 h after it began. When the fire started, record-setting maximum values were measured for all gases monitored at this site (specifically, peaks of 99,995 μg m−3 for CO, 951 μg m−3 for O3, 478 μg m−3 for NO2, 116 μg m−3 for SO2 and 1000 μg m−3 for PM10). According to the temporal evolution patterns of these species, the atmosphere over a burnt area can recover to initial atmospheric levels between 48 and 96 h after an event. The impact of the Doñana plume was studied using hourly forward trajectories computed with the HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory) model to analyse the emission source for the burnt area. The Doñana fire plume affected large metropolitan areas near the Mediterranean coast. Air quality stations located in the cities of Seville and Cadiz registered the arrival of the plume based on increases in CO and PM10. Using CO as a tracer, measurements from the AIRS and MOPITT instruments allowed us to observe the transport of the Doñana plume from the Strait of Gibraltar to the Mediterranean. Finally, after two days, the Doñana forest fire plume reached the western Mediterranean basin.

Trace metal enrichment during the Industrial Period recorded across an altitudinal transect in the Southern Central Pyrenees

J.P. Corella, A. Saiz-Lopez, M.J. Sierra, M.P.Matac, R. Millán, M. Morellón, C.A. Cuevas, A. Moreno, B.L. Valero-Garcés

Science of The Total Environment, Volume 645, 15 December 2018, Pages 761-772,



The study of three lacustrine sedimentary archives along an altitudinal transect in the Southern Central Pyrenees - lakes Estanya, Basa and Marboré- has provided a unique record of changes in anthropogenic trace metal concentrations over the last six centuries in NE Iberian Peninsula. Although site-specific processes influence metals enrichments in each lacustrine system, significant enrichments of Hg and Pb and minor to moderate enrichments of Cu, Cd, and Zn with respect to baseline (Pre-industrial) concentrations highlight intensive release of anthropogenic trace metals with the advent of the Industrial Revolution leading to maximum values during the 20th century. The largest trace metal pollution occurred between 1840s and 1920s CE mainly derived from the increasing demand of ore resources in Southern Europe during the Industrialization. A second, less distinct pollution phase occurred between 1950s and 1990s, associated with the “Great Acceleration” and increased trace metal emissions related to road-transport, use of fertilizers in agriculture and the global boost of the Chemical Industry. Enrichment of mercury during the Industrial Period correlates well with Hg production in Spanish Almadén mines and global emission inventories. Local mining in the Pyrenees and regional smelting activities in Spain and Southern France may explain the enrichment of lead (and associated by-products cadmium and zinc) during the first pollution phase while the use of leaded gasoline since the mid-20th century drives the higher Pb enrichment factor found till the late 20th century. This investigation demonstrates that environmental regulations controlling emissions of hazardous metals during the last decades have greatly contributed to a significant reduction of these anthropogenic trace metals enrichments in natural ecosystems although they still double pre-industrial levels. This study also exemplifies the different sensitiveness of lacustrine systems to record past atmospheric pollution phases and highlights the need of multi-archive studies to conduct regional (rather than local) pollution reconstructions.

Measurements of atmospheric HONO vertical distribution and temporalevolution in Madrid (Spain) using the MAX-DOAS technique

David Garcia-Nieto, Nuria Benavent, Alfonso Saiz-Lopez

Sci Total Environ. 2018; 643:957-966. doi: 10.1016/j.scitotenv.2018.06.180



Nitrous acid (HONO) stands as one of the main species in tropospheric chemistry, primarily in polluted, urban regions. Due to its fast photodissociation, it is considered as one the main sources of the hydroxyl radical (OH), the most relevant oxidant in the atmosphere. Therefore, the evaluation of HONO concentration profiles and their temporal evolution is important for urban atmospheric chemistry. In this study, we report a year-round measurement of HONO vertical concentration profiles, as well as their diurnal and seasonal evolution during 2016 in Madrid. Making use of the Multi-AXis Differential Absorption Spectroscopy (MAX-DOAS) technique in addition to inversion algorithms, we retrieved the aerosol extinction and trace gas concentrations. Our results show HONO maximum values of 3.5–4 ppbv in the early morning and late afternoon, and minima around noon, when the lifetime ofHONO against photolysis is shortest. On average, there is a pronounced HONO concentration gradient across different seasons, being higher during the autumn and winter months. Finally, we estimate and discuss the production rate of OH radicals from HONO photolysis, along with its variability throughout the year.

Stratospheric Injection of Brominated Very Short-Lived Substances: Aircraft Observations in the Western Pacific and Representation in Global Models

Pamela A. Wales , Ross J. Salawitch , Julie M. Nicely , Daniel C. Anderson , Timothy P. Canty, Sunil Baidar, Barbara Dix, Theodore K. Koenig, Rainer Volkamer , Dexian Chen, L. Gregory Huey , David J. Tanner, Carlos A. Cuevas , Rafael P. Fernandez , Douglas E. Kinnison, Jean-Francois Lamarque, Alfonso Saiz-Lopez, Elliot L. Atlas, Samuel R. Hall , Maria A. Navarro, Laura L. Pan, Sue M. Schauffler , Meghan Stell , Simone Tilmes, Kirk Ullmann , Andrew J. Weinheimer,  Hideharu Akiyoshi, Martyn P. Chipperfield , Makoto Deushi, Sandip S. Dhomse , Wuhu Feng, Phoebe Graf, Ryan Hossaini , Patrick Jöckel , Eva Mancini, Martine Michou, Olaf Morgenstern, Luke D. Oman , Giovanni Pitari , David A. Plummer , Laura E. Revell , Eugene Rozanov, David Saint-Martin, Robyn Schofield, Andrea Stenke , Kane A. Stone, Daniele Visioni, Yousuke Yamashita, and Guang Zeng

Journal of Geophysical Research:Atmospheres,Volume123, Issue10, Pages 5690-5719,



We quantify the stratospheric injection of brominated very short-lived substances (VSLS) based on aircraft observations acquired in winter 2014 above the Tropical Western Pacific during the CONvective TRansport of Active Species in the Tropics (CONTRAST) and the Airborne Tropical TRopopause Experiment (ATTREX) campaigns. The overall contribution of VSLS to stratospheric bromine was determined to be 5.0 ± 2.1 ppt, in agreement with the 5 ± 3 ppt estimate provided in the 2014 World Meteorological Organization (WMO) Ozone Assessment report (WMO 2014), but with lower uncertainty. Measurements of organic bromine compounds, including VSLS, were analyzed using CFC-11 as a reference stratospheric tracer. From this analysis, 2.9 ± 0.6 ppt of bromine enters the stratosphere via organic source gas injection of VSLS. This value is two times the mean bromine content of VSLS measured at the tropical tropopause, for regions outside of the Tropical Western Pacific, summarized in WMO 2014. A photochemical box model, constrained to CONTRAST observations, was used to estimate inorganic bromine from measurements of BrO collected by two instruments. The analysis indicates that 2.1 ± 2.1 ppt of bromine enters the stratosphere via inorganic product gas injection. We also examine the representation of brominated VSLS within 14 global models that participated in the Chemistry-Climate Model Initiative. The representation of stratospheric bromine in these models generally lies within the range of our empirical estimate. Models that include explicit representations of VSLS compare better with bromine observations in the lower stratosphere than models that utilize longer-lived chemicals as a surrogate for VSLS.

Rapid increase in atmospheric iodine levels in the North Atlantic since the mid-20th century

Carlos A. Cuevas, Niccolò Maffezzoli, Juan Pablo Corella, Andrea Spolaor, Paul Vallelonga, Helle A. Kjær, Marius Simonsen, Mai Winstrup, Bo Vinther, Christopher Horvat, Rafael P. Fernandez, Douglas Kinnison, Jean-François Lamarque, Carlo Barbante & Alfonso Saiz-Lopez.

Nature Communication 9, Article number:1452 (2018) 41467-018-03756-1



Atmospheric iodine causes tropospheric ozone depletion and aerosol formation, both of which have significant climate impacts, and is an essential dietary element for humans. However, the evolution of atmospheric iodine levels at decadal and centennial scales is unknown. Here, we report iodine concentrations in the RECAP ice-core (coastal East Greenland) to investigate how atmospheric iodine levels in the North Atlantic have evolved over the past 260 years (1750–2011), this being the longest record of atmospheric iodine in the Northern Hemisphere. The levels of iodine tripled from 1950 to 2010. Our results suggest that this increase is driven by anthropogenic ozone pollution and enhanced sub-ice phytoplankton production associated with the recent thinning of Arctic sea ice. Increasing atmospheric iodine has accelerated ozone loss and has considerably enhanced iodine transport and deposition to the Northern Hemisphere continents. Future climate and anthropogenic forcing may continue to amplify oceanic iodine emissions with potentially significant health and environmental impacts at global scale.

Application of a short term air quality action plan in Madrid (Spain) under a high-pollution episode - Part I: Diagnostic and analysis from observations

Application of a short term air quality action plan in Madrid (Spain) under a high-pollution episode - Part I: Diagnostic and analysis from observations. Rafael Borge, Begoña Artíñano, Carlos Yagüe, Francisco Javier Gomez-Moreno, Alfonso Saiz-Lopez, Mariano Sastre, Adolfo Narros, David García-Nieto, Nuria Benavent, Gregorio Maqueda

Science of The Total Environment,



Exceedances of NO2 hourly limit value (200 μg·m−3) imply the need to implement short term action plans to avoid adverse effects on human health in urban areas. The Madrid City Council applied the stage 3 of the NO2 protocol during a high-pollution episode under stable meteorological conditions on December 2016 for the first time. This included road traffic access restrictions to the city centre (50% of conventional private vehicles based on plate numbers). In this contribution we analyse different meteorological and air quality observations, including non-standard parameters (such as number of ultrafine particles and remote sensing techniques MAXDOAS) for a better understanding of the effectivity of short-term emission abatement measures under real conditions and to identify options to improve the NO2 protocol in the future. According to our results, the inversion base height computed from vertical temperature soundings is a meaningful index to anticipate very unfavourable conditions and trigger the actions included in the protocol. The analysis of the concentration levels of the main pollutants from the Madrid air quality monitoring network indicate that only stage 3 of the protocol had a significant effect on NO2 maximum concentrations. The restrictions applied may have prevented NO2 concentrations to further increase in the city centre (up to 15%) although pollution levels in the city outskirts, outside the area directly affected by the traffic restrictions, remained unchanged or may have been slightly increased. Nonetheless, further studies are needed to estimate more precisely the effect of the measures taken and to assess potential trade-offs. Our results suggest that emissions play an important role also under very strong stability conditions although drastic measures are needed to achieve a significant impact. This highlights the importance of an appropriate timing for short-term actions and the need of permanent abatement measures related to air quality plans and policies.

Phenomenology of summer ozone episodes over the Madrid Metropolitan Area, central Spain

Xavier Querol, Andrés Alastuey, Gotzon Gangoiti, Noemí Perez, Hong K. Lee, Heeram R. Eun, Yonghee Park, Enrique Mantilla, Miguel Escudero, Gloria Titos, Lucio Alonso, Brice Temime-Roussel, Nicolas Marchand, Juan R. Moreta, M. Arantxa Revuelta, Pedro Salvador, Begoña Artíñano, Saúl García dos Santos, Mónica Anguas, Alberto Notario, Alfonso Saiz-Lopez, Roy M. Harrison, Millán Millán, and Kang-Ho Ahn

Atmos. chem. phys.18, 6511-6511, 2018,



Various studies have reported that the photochemical nucleation of new ultrafine particles (UFPs) in urban environments within high insolation regions occurs simultaneously with high ground ozone (O3) levels. In this work, we evaluate the atmospheric dynamics leading to summer O3 episodes in the Madrid air basin (central Iberia) by means of measuring a 3-D distribution of concentrations for both pollutants. To this end, we obtained vertical profiles (up to 1200m above ground level) using tethered balloons and miniaturised instrumentation at a suburban site located to the SW of the Madrid Metropolitan Area (MMA), the Majadahonda site (MJDH), in July 2016. Simultaneously, measurements of an extensive number of air quality and meteorological parameters were carried out at three supersites across the MMA. Furthermore, data from O3 soundings and daily radio soundings were also used to interpret atmospheric dynamics.

The results demonstrate the concatenation of venting and accumulation episodes, with relative lows (venting) and peaks (accumulation) in O3 surface levels. Regardless of the episode type, the fumigation of high-altitude O3 (arising from a variety of origins) contributes the major proportion of surface O3 concentrations. Accumulation episodes are characterised by a relatively thinner planetary boundary layer (<1500m at midday, lower in altitude than the orographic features), light synoptic winds, and the development of mountain breezes along the slopes of the Guadarrama Mountain Range (located W and NW of the MMA, with a maximum elevation of >2400ma.s.l.). This orographic–meteorological setting causes the vertical recirculation of air masses and enrichment of O3 in the lower tropospheric layers. When the highly polluted urban plume from Madrid is affected by these dynamics, the highest Ox (O3+NO2) concentrations are recorded in the MMA.

Vertical O3 profiles during venting episodes, with strong synoptic winds and a deepening of the planetary boundary layer reaching >2000ma.s.l., were characterised by an upward gradient in O3 levels, whereas a reverse situation with O3 concentration maxima at lower levels was found during the accumulation episodes due to local and/or regional production. The two contributions to O3 surface levels (fumigation from high-altitude strata, a high O3 background, and/or regional production) require very different approaches for policy actions. In contrast to O3 vertical top-down transfer, UFPs are formed in the planetary boundary layer (PBL) and are transferred upwards progressively with the increase in PBL growth.

The influence of ocean halogen and sulfur emissions in the air quality of a coastal megacity: The case of Los Angeles

Muñiz-Unamunzaga M., Borge R, Sarwar G., Gantt B., de la Paz D., Cuevas CA., Saiz-Lopez A.

Sci Total Environ. 2018 Jan 1;610-611:1536-1545. doi: 10.1016/j.scitotenv.2017.06.098.



The differential optical absorption spectroscopy (DOAS) method is a well-known remote sensing technique that is nowadays widely used for measurements of atmospheric trace gases, creating the need for harmonization and characterization efforts. In this study, an intercomparison exercise of DOAS retrieval codes from 17 international groups is presented, focusing on NO2 slant columns. The study is based on data collected by one instrument during the Multi-Axis DOAS Comparison campaign for Aerosols and Trace gases (MAD-CAT) in Mainz, Germany, in summer 2013. As data from the same instrument are used by all groups, the results are free of biases due to instrumental differences, which is in contrast to previous intercomparison exercises. While in general an excellent correlation of NO2 slant columns between groups of >99.98% (noon The oceans are the main source of natural halogen and sulfur compounds, which have a significant influence on the oxidizing capacity of the marine atmosphere; however, their impact on the air quality of coastal cities is currently unknown. We explore the effect of marine halogens (Cl, Br and I) and dimethyl sulfide (DMS) on the air quality of a large coastal city through a set of high-resolution (4-km) air quality simulations for the urban area of Los Angeles, US, using the Community Multiscale Air Quality (CMAQ model). The results indicate that marine halogen emissions decrease ozone and nitrogen dioxide levels up to 5 ppbv and 2.5 ppbv, respectively, in the city of Los Angeles. Previous studies suggested that the inclusion of chlorine in air quality models leads to the generation of ozone in urban areas through photolysis of nitryl chloride (ClNO2). However, we find that when considering the chemistry of Cl, Br and I together the net effect is a reduction of surface ozone concentrations. Furthermore, combined ocean emissions of halogens and DMS cause substantial changes in the levels of key urban atmospheric oxidants such as OH, HO2 and NO3, and in the composition and mass of fine particles. Although the levels of ozone, NO3 and HOx are reduced, we find a 10% increase in secondary organic aerosol (SOA) mean concentration, attributed to the increase in aerosol acidity and sulfate aerosol formation when combining DMS and bromine. Therefore, this new pathway for enhanced SOA formation may potentially help with current model under predictions of urban SOA. Although further observations and research are needed to establish these preliminary conclusions, this first city-scale investigation suggests that the inclusion of oceanic halogens and DMS in air quality models may improve regional air quality predictions over coastal cities around the worldfits) and >99.2% (sequential reference fits) for all elevation angles is found, differences between individual retrievals are as large as 8% for NO2 slant columns and 100% for rms residuals
in small elevation angles above the horizon. Comprehensive sensitivity studies revealed that absolute slant column differences result predominantly from the choice of the reference spectrum while relative differences originate from the numerical approach for solving the DOAS equation as well as the treatment of the slit function. Furthermore, differences in the implementation of the intensity offset correction were found to produce disagreements for measurements close to sunrise (8–10% for NO2, 80% for rms residual). The largest effect of 8% difference in NO2 was found to arise from the reference treatment; in particular
for fits using a sequential reference. In terms of rms fit residual, the reference treatment has only a minor impact. In contrast, the wavelength calibration as well as the intensity offset correction were found to have the largest impact (up to 80 %) on rms residual while having only a minor impact on retrieved NO2 slant columns.

Tropospheric Ozone Assessment Report: Assessment of global-scale model performance for global and regional ozone distributions, variability, and trends

P. J. Young, V. Naik, A. M. Fiore, A. Gaudel, J. Guo, M. Y. Lin, J. Neu, D. D. Parrish, H. E. Rieder, J. L. Schnell, S. Tilmes, O. Wild, L. Zhang, J. Brandt, A. Delcloo, R. M. Doherty, C. Geels, M. I. Hegglin, L. Hu, U.  Im,  R.  Kumar,  A.  Luhar, L.  Murray, D. Plummer, J. Rodriguez, A. Saiz-Lopez, M. G. Schultz, M. Woodhouse, G. Zeng, and J. Ziemke

Elem Sci Anth, 6: 10. DOI:



This study quantifies the present-day global and regional distributions (2010–2014) and trends (2000–2014) for five ozone metrics relevant for short-term and long-term human exposure. These metrics, calculated by the Tropospheric Ozone Assessment Report, are: 4th highest daily maximum 8-hour ozone (4MDA8); number of days with MDA8 > 70 ppb (NDGT70), SOMO35 (annual Sum of Ozone Means Over 35 ppb) and two seasonally averaged metrics (3MMDA1; AVGMDA8). These metrics were explored at ozone monitoring sites worldwide, which were classified as urban or non-urban based on population and nighttime lights data.

Present-day distributions of 4MDA8 and NDGT70, determined predominantly by peak values, are similar with highest levels in western North America, southern Europe and East Asia. For the other three metrics, distributions are similar with North–South gradients more prominent across Europe and Japan. Between 2000 and 2014, significant negative trends in 4MDA8 and NDGT70 occur at most US and some European sites. In contrast, significant positive trends are found at many sites in South Korea and Hong Kong, with mixed trends across Japan. The other three metrics have similar, negative trends for many non-urban North American and some European and Japanese sites, and positive trends across much of East Asia. Globally, metrics at many sites exhibit non-significant trends. At 59% of all sites there is a common direction and significance in the trend across all five metrics, whilst 4MDA8 and NDGT70 have a common trend at ~80% of all sites. Sensitivity analysis shows AVGMDA8 trends differ with averaging period (warm season or annual). Trends are unchanged at many sites when a 1995–2014 period is used; although fewer sites exhibit non-significant trends. Over the longer period 1970–2014, most Japanese sites exhibit positive 4MDA8/SOMO35 trends. Insufficient data exist to characterize ozone trends for the rest of Asia and other world regions.

BrO and inferred Bry profiles over the western Pacific: relevance of inorganic bromine sources and a Bry minimum in the aged tropical tropopause layer

Theodore K. Koenig, Rainer Volkamer, Sunil Baidar, Barbara Dix, Siyuan Wang, Daniel C. Anderson, Ross J. Salawitch, Pamela A. Wales, Carlos A. Cuevas, Rafael P. Fernandez, Alfonso Saiz-Lopez, Mathew J. Evans, Tomás Sherwen, Daniel J. Jacob, Johan Schmidt, Douglas Kinnison, Jean-François Lamarque, Eric C. Apel, James C. Bresch, Teresa Campos, Frank M. Flocke, Samuel R. Hall, Shawn B. Honomichl, Rebecca Hornbrook, Jørgen B. Jensen, Richard Lueb, Denise D. Montzka, Laura L. Pan, J. Michael Reeves, Sue M. Schauffler, Kirk Ullmann, Andrew J. Weinheimer, Elliot L. Atlas, Valeria Donets, Maria A. Navarro, Daniel Riemer, Nicola J. Blake, Dexian Chen, L. Gregory Huey, David J. Tanner, Thomas F. Hanisco, and Glenn M. Wolfe

Atmos. Chem. Phys., 17, 15245-15270, 2017,



We report measurements of bromine monoxide (BrO) and use an observationally constrained chemical box model to infer total gas-phase inorganic bromine (Bry) over the tropical western Pacific Ocean (tWPO) during the CONTRAST field campaign (January–February 2014). The observed BrO and inferred Bry profiles peak in the marine boundary layer (MBL), suggesting the need for a bromine source from sea-salt aerosol (SSA), in addition to organic bromine (CBry). Both profiles are found to be C-shaped with local maxima in the upper free troposphere (FT). The median tropospheric BrO vertical column density (VCD) was measured as 1.6×1013 molec cm−2, compared to model predictions of 0.9×1013 molec cm−2 in GEOS-Chem (CBry but no SSA source), 0.4×1013 molec cm−2 in CAM-Chem (CBry and SSA), and 2.1×1013 molec cm−2 in GEOS-Chem (CBry and SSA). Neither global model fully captures the C-shape of the Bry profile. A local Bry maximum of 3.6 ppt (2.9–4.4 ppt; 95 % confidence interval, CI) is inferred between 9.5 and 13.5 km in air masses influenced by recent convective outflow. Unlike BrO, which increases from the convective tropical tropopause layer (TTL) to the aged TTL, gas-phase Bry decreases from the convective TTL to the aged TTL. Analysis of gas-phase Bry against multiple tracers (CFC-11, H2O ∕ O3 ratio, and potential temperature) reveals a Bry minimum of 2.7 ppt (2.3–3.1 ppt; 95 % CI) in the aged TTL, which agrees closely with a stratospheric injection of 2.6 ± 0.6 ppt of inorganic Bry (estimated from CFC-11 correlations), and is remarkably insensitive to assumptions about heterogeneous chemistry. Bry increases to 6.3 ppt (5.6–7.0 ppt; 95 % CI) in the stratospheric "middleworld" and 6.9 ppt (6.5–7.3 ppt; 95 % CI) in the stratospheric "overworld". The local Bry minimum in the aged TTL is qualitatively (but not quantitatively) captured by CAM-Chem, and suggests a more complex partitioning of gas-phase and aerosol Bry species than previously recognized. Our data provide corroborating evidence that inorganic bromine sources (e.g., SSA-derived gas-phase Bry) are needed to explain the gas-phase Bry budget in the upper free troposphere and TTL. They are also consistent with observations of significant bromide in Upper Troposphere–Lower Stratosphere aerosols. The total Bry budget in the TTL is currently not closed, because of the lack of concurrent quantitative measurements of gas-phase Bry species (i.e., BrO, HOBr, HBr, etc.) and aerosol bromide. Such simultaneous measurements are needed to (1) quantify SSA-derived Bry in the upper FT, (2) test Bry partitioning, and possibly explain the gas-phase Bry minimum in the aged TTL, (3) constrain heterogeneous reaction rates of bromine, and (4) account for all of the sources of Bry to the lower stratosphere.

Formaldehyde in the Tropical Western Pacific: Chemical Sources and Sinks, Convective Transport, and Representation in CAM-Chem and the CCMI Models

Daniel C. Anderson, Julie M. Nicely, Glenn M. Wolfe, Thomas F. Hanisco, Ross J. Salawitch, Timothy P. Canty, Russell R. Dickerson, Eric C. Apel, Sunil Baidar, Thomas J. Bannan, Nicola J. Blake, Dexian Chen, Barbara Dix, Rafael P. Fernandez, Samuel R. Hall, Rebecca S. Hornbrook, L. Gregory Huey, Beatrice Josse, Patrick Jöckel, Douglas E. Kinnison, Theodore K. Koenig, Michael Le Breton, Virginie Marécal, Olaf Morgenstern, Luke D. Oman, Laura L. Pan, Carl Percival, David Plummer, Laura E. Revell, Eugene Rozanov, Alfonso Saiz-Lopez, Andrea Stenke, Kengo Sudo, Simone Tilmes , Kirk Ullmann, Rainer Volkamer , Andrew J. Weinheimer, and Guang Zeng

Journal of Geophysical Research: Atmospheres, Volume 122, Issue 20, 27 October 2017, Pages 11,201–11,226, DOI: 10.1002/2016JD026121



Formaldehyde (HCHO) directly affects the atmospheric oxidative capacity through its effects on HOx. In remote marine environments, such as the tropical western Pacific (TWP), it is particularly important to understand the processes controlling the abundance of HCHO because model output from these regions is used to correct satellite retrievals of HCHO. Here we have used observations from the Convective Transport of Active Species in the Tropics (CONTRAST) field campaign, conducted during January and February 2014, to evaluate our understanding of the processes controlling the distribution of HCHO in the TWP as well as its representation in chemical transport/climate models. Observed HCHO mixing ratios varied from ~500 parts per trillion by volume (pptv) near the surface to ~75 pptv in the upper troposphere. Recent convective transport of near surface HCHO and its precursors, acetaldehyde and possibly methyl hydroperoxide, increased upper tropospheric HCHO mixing ratios by ~33% (22 pptv); this air contained roughly 60% less NO than more aged air. Output from the CAM-Chem chemistry transport model (2014 meteorology) as well as nine chemistry climate models from the Chemistry-Climate Model Initiative (free-running meteorology) are found to uniformly underestimate HCHO columns derived from in situ observations by between 4 and 50%. This underestimate of HCHO likely results from a near factor of two underestimate of NO in most models, which strongly suggests errors in NOx emissions inventories and/or in the model chemical mechanisms. Likewise, the lack of oceanic acetaldehyde emissions and potential errors in the model acetaldehyde chemistry lead to additional underestimates in modeled HCHO of up to 75 pptv (~15%) in the lower troposphere

Modeling the inorganic bromine partitioning in the tropical tropopause layer over the eastern and western Pacific Ocean

Maria A. Navarro, Alfonso Saiz-Lopez, Carlos A. Cuevas, Rafael P. Fernandez, Elliot Atlas, Xavier Rodriguez-Lloveras, Douglas Kinnison, Jean-Francois Lamarque, Simone Tilmes, Troy Thornberry, Andrew Rollins, James W. Elkins, Eric J. Hintsa, and Fred L. Moore

Atmos. Chem. Phys., 17, 9917-9930, 2017



The stratospheric inorganic bromine (Bry) burden arising from the degradation of brominated very short-lived organic substances (VSLorg) and its partitioning between reactive and reservoir species is needed for a comprehensive assessment of the ozone depletion potential of brominated trace gases. Here we present modeled inorganic bromine abundances over the Pacific tropical tropopause based on aircraft observations of VSLorg from two campaigns of the Airborne Tropical TRopopause EXperiment (ATTREX 2013, carried out over the eastern Pacific, and ATTREX 2014, carried out over the western Pacific) and chemistry-climate simulations (along ATTREX flight tracks) using the specific meteorology prevailing. Using the Community Atmosphere Model with Chemistry (CAM-Chem) we model that BrO and Br are the daytime dominant species. Integrated across all ATTREX flights, BrO represents ∼ 43 and 48 % of daytime Bry abundance at 17 km over the western and eastern Pacific, respectively. The results also show zones where Br / BrO > 1 depending on the solar zenith angle (SZA), ozone concentration, and temperature. On the other hand, BrCl and BrONO2 were found to be the dominant nighttime species with ∼  61 and 56 % of abundance at 17 km over the western and eastern Pacific, respectively. The western-to-eastern differences in the partitioning of inorganic bromine are explained by different abundances of ozone (O3), nitrogen dioxide (NO2), total inorganic chlorine (Cly), and the efficiency of heterogeneous reactions of bromine reservoirs (mostly BrONO2 and HBr) occurring on ice crystals.

Unexpected increase in the oxidation capacity of the urban atmosphere of Madrid, Spain

A. Saiz-Lopez, R. Borge, A. Notario, J. A. Adame, D. de la Paz, X. Querol, B. Artíñano, F. J. Gómez-Moreno & C. A. Cuevas

Scientific Reports 7, Article number: 45956 (2017) doi:10.1038/srep45956



Atmospheric oxidants such as ozone (O3), hydroxyl and nitrate radicals (OH and NO3) determine the ability of the urban atmosphere to process organic and inorganic pollutants, which have an impact on air quality, environmental health and climate. Madrid city has experienced an increase of 30–40% in ambient air O3 levels, along with a decrease of 20–40% in NO2, from 2007 to 2014. Using air pollution observations and a high-resolution air quality model, we find a large concentration increase of up to 70% and 90% in OH and NO3, respectively, in downtown Madrid (domain-wide average increase of 10% and 32% for OH and NO3, respectively). The results also show an 11% reduction in the nitric acid concentrations, leading to a remarkable denoxification of this urban atmosphere with implications for lower PM2.5 levels and nitrogen input into ecosystems. This study suggests that projected worldwide NOx emission reductions, following air quality standards, will lead to important changes in the oxidizing capacity of the atmosphere in and around large cities.

Investigating differences in DOAS retrieval codes using MAD-CAT campaign data

Enno Peters , Gaia Pinardi, André Seyler, Andreas Richter, Folkard Wittrock, Tim Bösch, Michel Van Roozendael, François Hendrick, Theano Drosoglou, Alkiviadis F. Bais, Yugo Kanaya, Xiaoyi Zhao, Kimberly Strong, Johannes Lampel, Rainer Volkamer, Theodore Koenig, Ivan Ortega, Olga Puentedura, Mónica Navarro-Comas, Laura Gómez, Margarita Yela González, Ankie Piters, Julia Remmers, Yang Wang, ThomasWagner, ShanshanWang,  Alfonso Saiz-Lopez, David García-Nieto, Carlos A. Cuevas, Nuria Benavent, Richard Querel, Paul Johnston, Oleg Postylyakov, Alexander Borovski, Alexander Elokhov, Ilya Bruchkouski, Haoran Liu, Cheng Liu, Qianqian Hong, Claudia Rivera, Michel Grutter, Wolfgang Stremme, M. Fahim Khokhar, Junaid Khayyam, John P. Burrows

Atmospheric Measurement Techniques, Volume 10, Issue 3, pp  955-978, doi:10.5194/amt-10-955-2017, 2017.Atmospheric Environment, Volume 155, pp 97-107;, 2017.02.018



The differential optical absorption spectroscopy (DOAS) method is a well-known remote sensing technique that is nowadays widely used for measurements of atmospheric trace gases, creating the need for harmonization and characterization efforts. In this study, an intercomparison exercise of DOAS retrieval codes from 17 international groups is presented, focusing on NO2 slant columns. The study is based on data collected by one instrument during the Multi-Axis DOAS Comparison campaign for Aerosols and Trace gases (MAD-CAT) in Mainz, Germany, in summer 2013. As data from the same instrument are used by all groups, the results are free of biases due to instrumental differences, which is in contrast to previous intercomparison exercises. While in general an excellent correlation of NO2 slant columns between groups of >99.98% (noon reference fits) and >99.2% (sequential reference fits) for all elevation angles is found, differences between individual retrievals are as large as 8% for NO2 slant columns and 100% for rms residuals
in small elevation angles above the horizon. Comprehensive sensitivity studies revealed that absolute slant column differences result predominantly from the choice of the reference spectrum while relative differences originate from the numerical approach for solving the DOAS equation as well as the treatment of the slit function. Furthermore, differences in the implementation of the intensity offset correction were found to produce disagreements for measurements close to sunrise (8–10% for NO2, 80% for rms residual). The largest effect of 8% difference in NO2 was found to arise from the reference treatment; in particular
for fits using a sequential reference. In terms of rms fit residual, the reference treatment has only a minor impact. In contrast, the wavelength calibration as well as the intensity offset correction were found to have the largest impact (up to 80 %) on rms residual while having only a minor impact on retrieved NO2 slant columns.

700 years reconstruction of mercury and lead atmospheric deposition in the Pyrenees (NE Spain)

J.P. Corella, B.L. Valero-Garcés,  F. Wang , A. Martínez-Cortizas, C.A. Cuevas, A. Saiz-Lopez

Atmospheric Environment, Volume 155, pp 97-107;, 2017.02.018



Geochemical analyses in varved lake sediment cores (Lake Montcortes, Pre-Pyrenees) allowed reconstruction of mercury (Hg) and lead (Pb) atmospheric deposition over the past seven centuries in the Pyrenees (NE Spain). Accumulation Rates (AR) from the Middle Ages to the Industrial Period ranged from 2500 to 26130 mg m2.y1 and 15e152 mg m2.y1 for Pb and Hg respectively. Significant metal pollution started ca CE 1550 during a period of increased exploitation of ore resources in Spain. Colder and humid conditions in the Pyrenees during the Little Ice Age may have also favoured Hg and Pb atmospheric deposition in the lake. Therefore, the interplay between increased rainfall (wet deposition) and mining activities in the Iberian Peninsula has driven Hg and Pb AR during the Pre-industrial Period. More recently, the use of leaded gasoline in Europe in the mid-20th century may explain the highest Pb AR between CE 1953 and 1971. The highest Hg AR occurred in CE 1940 synchronous with the highest Hg production peak in Almaden mining district (southern Spain) and the Second World War. The record of Hg enrichment in Lake Montcortes shows a decrease during the last decades in Western Europe similar to other regional records and global emission models. This study highlights the exceptional quality of varved sequences to tease apart pollutants depositional mechanisms, identify historical periods of increased atmospheric pollution and provide a historical context for pollutant baseline values to make correct assessments of recent (atmospheric) pollution in lake ecosystems.

Sea-ice-related halogen enrichment at Law Dome, coastal East Antarctica

Paul Vallelong, Niccolo Maffezzoli, Andrew D. Moy, Mark A. J. Curran, Tessa R. Vance, Ross Edwards, Gwyn Hughes, Emily Barker, Gunnar Spreen, Alfonso Saiz-Lopez, J. Pablo Corella6, Carlos A. Cuevas, and Andrea Spolaor.

Climate of the Past, Vol 13, Issue 2, 27 February 2017, Pages 171-184 ; doi:10.5194/cp-13-171-2017, 2017



The Law Dome site is ideal for the evaluation of sea ice proxies due to its location near to the Antarctic coast, regular and high accumulation throughout the year, an absence of surface melting or remobilization, and minimal multiyear sea ice.We present records of bromine and iodine concentrations and their enrichment beyond seawater compositions and compare these to satellite observations of first-year sea ice area in the 90–130 E sector of the Wilkes coast. Our findings support the results of previous studies of sea ice variability from Law Dome, indicating that Wilkes coast sea ice area is currently at its lowest level since the start of the 20th century. From the Law Dome DSS1213 firn core, 26 years of monthly deposition data indicate that the period of peak bromine enrichment is during austral spring–summer, from November to February. Results from a traverse along the lee (western) side of Law Dome show low levels of sodium and bromine deposition, with the greatest fluxes in the vicinity of the Law Dome summit. Finally, multidecadal variability in iodine enrichment appears well correlated to bromine enrichment, suggesting a common source of variability that may be related to the Interdecadal Pacific Oscillation (IPO).

On the summertime air quality and related photochemical processes in the megacity Shanghai, China

Ka Lok Chan, ShanshanWang, Cheng Liu, Bin Zhou, Mark O.Wenig, Alfonso Saiz-Lopez.

Science of The Total Environment, Vol. 580, 15 February 2017, Pages 974–983;



Summertime surface ozone (O3) and related secondary formation of fine particles are the major air quality concerns in the megacity of Shanghai. We performed mobile Cavity Enhanced Differential Optical Absorption Spectroscopy (CE-DOAS) measurements to investigate the spatial distribution of on-road nitrogen dioxide (NO2) concentrations along the Inner Ring Elevated Road (IRER) in Shanghai. The observations show a ratio of 4 between CE-DOAS averaged on-road NO2 and the in-situ ambient measurements, illustrating the strong impact of vehicle emissions over the urban area. The air mass transport analysis suggests that the observed episodic ozone events arise from both the abundance of volatile organic compounds (VOCs) precursors in the sampled plume and the regional transport of ozone-rich air masses. Analysis of the sources of PM2.5 shows that the secondary heterogeneous gas-to-particle conversion of sulfate and nitrate from sulfur dioxide (SO2) and nitrogen oxides (NOx) is the largest source of PM2.5 contributing 44.8 ± 9.2% of the total PM2.5. Ozone-related photochemical formation of fine particles is estimated to contribute about 22.5 ± 11.9% of the total PM2.5, which is strongly facilitated by solar radiation in summer. According to our results, nitrous acid (HONO) is the major precursor of hydroxyl radicals (OH) accounting for 40% to 80% of the total OH production during daytime. A significant correlation is found between the HONO levels in the early morning and the daily O3 and PM2.5 levels. The summertime measurements indicate that the photolytic reaction of HONO after sunrise increased the abundance of daytime OH and oxidative capacity, resulting in an enhancement of ground level ozone and secondary organic aerosol formation. This study provides quantitative information to better understand photochemical formation of ozone and fine particles in Shanghai during summertime, which is useful for designing collaborative strategies to mitigate emissions of precursor pollutants.

Impact of biogenic very short-lived bromine on the Antarctic ozone hole during the 21st century

Rafael P. Fernandez, Douglas E. Kinnison, Jean-Francois Lamarque, Simone Tilmes, and Alfonso Saiz-Lopez.

Atmos. Chem. Phys., 17, 1673-1688, 2017; doi:10.5194/acp-17-1673-2017



Active bromine released from the photochemical decomposition of biogenic very short-lived bromocarbons (VSLBr) enhances stratospheric ozone depletion. Based on a dual set of 1960–2100 coupled chemistry–climate simulations (i.e. with and without VSLBr), we show that the maximum Antarctic ozone hole depletion increases by up to 14 % when natural VSLBr are considered, which is in better agreement with ozone observations. The impact of the additional 5 pptv VSLBr on Antarctic ozone is most evident in the periphery of the ozone hole, producing an expansion of the ozone hole area of ∼ 5 million km2, which is equivalent in magnitude to the recently estimated Antarctic ozone healing due to the implementation of the Montreal Protocol. We find that the inclusion of VSLBr in CAM-Chem (Community Atmosphere Model with Chemistry, version 4.0) does not introduce a significant delay of the modelled ozone return date to 1980 October levels, but instead affects the depth and duration of the simulated ozone hole. Our analysis further shows that total bromine-catalysed ozone destruction in the lower stratosphere surpasses that of chlorine by the year 2070 and indicates that natural VSLBr chemistry would dominate Antarctic ozone seasonality before the end of the 21st century. This work suggests a large influence of biogenic bromine on the future Antarctic ozone layer.

The Impact of Iodide-Mediated Ozone Deposition and Halogen Chemistry on Surface Ozone Concentrations Across the Continental United States

Brett Gantt, Golam Sarwar, Jia Xing, Heather Simon, Donna Schwede, William T. Hutzell, Rohit Mathur,  Alfonso Saiz-Lopez

Environ. Sci. Technol., 2017, 51 (3), pp 1458–1466; doi: 10.1021/acs.est.6b03556.



The air quality of many large coastal areas in the United States is affected by the confluence of polluted urban and relatively clean marine airmasses, each with distinct atmospheric chemistry. In this context, the role of iodide-mediated ozone (O3) deposition over seawater and marine halogen chemistry accounted for in both the lateral boundary conditions and coastal waters surrounding the continental U.S. is examined using the Community Multiscale Air Quality (CMAQ) model. Several nested simulations are conducted in which these halogen processes are implemented separately in the continental U.S. and hemispheric CMAQ domains, the latter providing lateral boundary conditions for the former. Overall, it is the combination of these processes within both the continental U.S. domain and from lateral boundary conditions that lead to the largest reductions in modeled surface O3 concentrations. Predicted reductions in surface O3 concentrations occur mainly along the coast where CMAQ typically has large overpredictions. These results suggest that a  realistic representation of halogen processes in marine regions can improve model prediction of O3 concentrations near the coast.

Thermochemistry of halogen-containing organic compounds with influence on atmospheric chemistry.

Juan Z. Dávalos, Rafael Notario, Carlos A. Cuevas, Josep M. Oliva, Alfonso Saiz-Lopez.

Computational and Theoretical Chemistry, Volume 1099, 1 January 2017, Pages 36–44; DOI:org/10.1016/j.comptc.2016.11.009



We report a study on the thermochemical properties of a wide variety of halogen-containing organic compounds with relevance on several atmospheric chemical processes, such as catalytic ozone destruction. In particular, we have computationally determined the standard molar enthalpies of formation, Δf Hm° (g), and the carbon-halogen bond dissociation enthalpies, BDE, in the gas phase at 298.15 K. A reliable estimation of these thermodynamic magnitudes was deduced, using atomization and isodesmic reactions methodologies, from ab initio computational methods. The enthalpies of formation of the radicals formed through bond dissociations have also been computed.

The Convective Transport of Active Species in the Tropics (CONTRAST) Experiment

L.L.Pan, E.L.Atlas, R.J.Salawitch, S.B.Honomichl, J.F.Bresch, W.J.Randel, E.C.Apel, R.S.Hornbrook, A.J.Weinheimer, D.C.Anderson, S.J.Andrews, S.Baidar, S.P.Beatn, T.L.Campos, L.J.Carpenter, D.Chen, B.Dix, V.Donets, S.R.Hall, T.F.Hanisco, C.R.Homyer, L.G.Huey, J.B.Jensen, L.Kaser, D.E.Kinnison, T.K.Koenig, J-­FLamarque, C.Liu, J.Luo, Z.J.Luo, D.D.Montzka, J.M.Nicely, R.B.Pierce, D.D.Riemer, T.Robinson, P.Romashkin, A.Saiz­Lopez, S.Schauffler, O.Shieh, M.H.Stell1, G.Vaughan, K.Ullmann, R.Volkamer, G.Wlfe.

Bull. Amer. Meteor. Soc., 0, DOI: 10.1175/BAMS-D-14-00272.1,2016



Airborne observations over the tropical western Pacific warm pool characterize the role of tropical convection in linking oceanic processes to ozone chemistry in the upper troposphere and lower stratosphere

The Convective Transport of Active Species in the Tropics (CONTRAST) experiment was conducted from Guam (13.5° N, 144.8° E) during January-February 2014. Using the NSF/NCAR Gulfstream V research aircraft, the experiment investigated the photochemical environment over the tropical western Pacific (TWP) warm pool, a region of massive deep convection and the major pathway for air to enter the stratosphere during Northern Hemisphere (NH) winter. The new observations provide a wealth of information for quantifying the influence of convection on the vertical distributions of active species. The airborne in situ measurements up to 15 km altitude fill a significant gap by characterizing the abundance and altitude variation of a wide suite of trace gases. These measurements, together with observations of dynamical and microphysical parameters, provide significant new data for constraining and evaluating global chemistry climate models. Measurements include precursor and product gas species of reactive halogen compounds that impact ozone in the upper troposphere/lower stratosphere. High accuracy, in-situ measurements of ozone obtained during CONTRAST quantify ozone concentration profiles in the UT, where previous observations from balloon-borne ozonesondes were often near or below the limit of detection. CONTRAST was one of the three coordinated experiments to observe the TWP during January-February 2014. Together, CONTRAST, ATTREX and CAST, using complementary capabilities of the three aircraft platforms as well as ground-based instrumentation, provide a comprehensive quantification of the regional distribution and vertical structure of natural and pollutant trace gases in the TWP during NH winter, from the oceanic boundary to the lower stratosphere.

# Now at Lanzhou University, Lanzhou, China

Contact information of the corresponding author: Laura L. Pan, National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307-3000, Email: This email address is being protected from spambots. You need JavaScript enabled to view it., Phone: 303-497-1467

Tropospheric emissions: Monitoring of pollution (TEMPO)

P.Zoogman; X.Liu; R.M.Suleiman; W.F.Pennington; D.E.Flittner; J.A.Al-Saadi; B.B.Hilton; D.K.Nicks; M.J.Newchurch; L.Carr; S.J.Janz; M.R. Andraschko; A.Arola; B.D.Baker; B.P.Canova; C.ChanMiller; R.C. Cohen; J.E.Davis; M.E.Dussault; D.P.Edwards; J.Fishman; A.Ghulam; G. GonzálezAbad; M.Grutter; J.R.Hermanm; J.Houck; D.J.Jacob; J.Joiner; B.J. Kerridge; J.Kim; N.A.Krotkov; L.Lamsal; C.Li; A.Lindfors; R.V. Martin; C.T.M. Elroy; C.McLinden; V.Natraj; D.O.Neil; C.R.Nowlan; E.J. O'Sullivan; P.I.Palmer; R.B.Pierce; M.R.Pippin; A.Saiz-Lopez; R.J.D. Spurr; J.J.Szykman; O.Torres; J.P.Veefkind; B.Veihelmann; H. Wang; J.Wang; K.Chance.

J. Quant. Spectrosc. Radiat. Transfer., ,2016



TEMPO was selected in 2012 by NASA as the first Earth Venture Instrument, for launch between 2018 and 2021. It will measure atmospheric pollution for greater North America from space using ultraviolet and visible spectroscopy. TEMPO observes from Mexico City, Cuba, and the Bahamas to the Canadian oil sands, and from the Atlantic to the Pacific, hourly and at high spatial resolution (~2.1 km N/S×4.4 km E/W at 36.5°N, 100°W). TEMPO provides a tropospheric measurement suite that includes the key elements of tropospheric air pollution chemistry, as well as contributing to carbon cycle knowledge. Measurements are made hourly from geostationary (GEO) orbit, to capture the high variability present in the diurnal cycle of emissions and chemistry that are unobservable from current low-Earth orbit (LEO) satellites that measure once per day. The small product spatial footprint resolves pollution sources at sub-urban scale. Together, this temporal and spatial resolution improves emission inventories, monitors population exposure, and enables effective emission-control strategies.

TEMPO takes advantage of a commercial GEO host spacecraft to provide a modest cost mission that measures the spectra required to retrieve ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), formaldehyde (H2CO), glyoxal (C2H2O2), bromine monoxide (BrO), IO (iodine monoxide), water vapor, aerosols, cloud parameters, ultraviolet radiation, and foliage properties. TEMPO thus measures the major elements, directly or by proxy, in the tropospheric O3 chemistry cycle. Multi-spectral observations provide sensitivity to O3 in the lowermost troposphere, substantially reducing uncertainty in air quality predictions. TEMPO quantifies and tracks the evolution of aerosol loading. It provides these near-real-time air quality products that will be made publicly available. TEMPO will launch at a prime time to be the North American component of the global geostationary constellation of pollution monitoring together with the European Sentinel-4 (S4) and Korean Geostationary Environment Monitoring Spectrometer (GEMS) instruments.

Ab initio quantum–chemical computations of the electronic states in HgBr2 and IBr: Molecules of interest on the Earth’s atmosphere

Sebastian P. Sitkiewicz, Josep M. Oliva, Juan Z. Dávalos, Rafael Notario, Alfonso Saiz–Lopez, Diego R. Alcoba, Ofelia B. Oña, and Daniel Roca-Sanjuán

J. Chem. Phys. Volum.145, 244304 (2016), doi: 10.1063/1.4971856



The electronic states of atmospheric relevant molecules IBr and HgBr2 are reported, within the UV-Vis spectrum range (170 nm ≤ λphoton ≤ 600 nm) by means of the complete–active–space self–consistent field/multi–state complete–active–space second–order perturbation theory/spin–orbit restricted–active–space state–interaction (CASSCF/MS–CASPT2/SO–RASSI) quantum–chemical approach and atomic–natural–orbital relativistic–correlation–consistent (ANO–RCC) basis sets. Several analyses of the methodology were carried out in order to reach converged results and therefore to establish a highly accurate level of theory. Good agreement is found with the experimental data with errors not higher than around 0.1 eV. The presented analyses shall allow upcoming studies aimed to accurately determine the absorption cross sections of interhalogen molecules and compounds with Hg that are relevant to better comprehend the photochemical processes taking place in the atmosphere.

Nighttime atmospheric chemistry of iodine

Alfonso Saiz-Lopez, John M. C. Plane, Carlos A. Cuevas, Anoop S. Mahajan, Jean-François Lamarque, and Douglas E. Kinnison

J. Chem. Phys. Volum.145, 244304 (2016), doi: 10.1063/1.4971856



Little attention has so far been paid to the nighttime atmospheric chemistry of iodine species. Current atmospheric models predict a buildup of HOI and I2 during the night that leads to a spike of IO at sunrise, which is not observed by measurements. In this work, electronic structure calculations are used to survey possible reactions that HOI and I2 could undergo at night in the lower troposphere, and hence reduce their nighttime accumulation. The new reaction NO3+ HOI  →  IO + HNO3 is proposed, with a rate coefficient calculated from statistical rate theory over the temperature range 260–300 K and at a pressure of 1000 hPa to be k(T)  =  2.7  ×  10−12(300 K/T)2.66 cm3 molecule−1 s−1. This reaction is included in two atmospheric models, along with the known reaction between I2 and NO3, to explore a new nocturnal iodine radical activation mechanism. The results show that this iodine scheme leads to a considerable reduction of nighttime HOI and I2, which results in the enhancement of more than 25 % of nighttime ocean emissions of HOI + I2and the removal of the anomalous spike of IO at sunrise. We suggest that active nighttime iodine can also have a considerable, so far unrecognized, impact on the reduction of the NO3 radical levels in the marine boundary layer (MBL) and hence upon the nocturnal oxidizing capacity of the marine atmosphere. The effect of this is exemplified by the indirect effect on dimethyl sulfide (DMS) oxidation.

A global model of tropospheric chlorine chemistry: Organic versus inorganic sources and impact on methane oxidation

Ryan Hossaini, Martyn P. Chipperfield, Alfonso Saiz-Lopez, Rafael Fernández, Sarah Monks, Wufu Feng, Peter Brauer, Roland von Glasow

J. Geophys. Res. Atmos. Volum.121, Pag. 14271-14297, doi: 10.1002/2016JD025756



Chlorine atoms (Cl) are highly reactive toward hydrocarbons in the Earth's troposphere, including the greenhouse gas methane (CH4). However, the regional and global CH4 sink from Cl is poorly quantified as tropospheric Cl concentrations ([Cl]) are uncertain by ~2 orders of magnitude. Here we describe the addition of a detailed tropospheric chlorine scheme to the TOMCAT chemical transport model. The model includes several sources of tropospheric inorganic chlorine (Cly), including (i) the oxidation of chlorocarbons of natural (CH3Cl, CHBr2Cl, CH2BrCl, and CHBrCl2) and anthropogenic (CH2Cl2, CHCl3, C2Cl4, C2HCl3, and CH2ClCH2Cl) origin and (ii) sea-salt aerosol dechlorination. Simulations were performed to quantify tropospheric [Cl], with a focus on the marine boundary layer, and quantify the global significance of Cl atom CH4 oxidation. In agreement with observations, simulated surface levels of hydrogen chloride (HCl), the most abundant Cly reservoir, reach several parts per billion (ppb) over polluted coastal/continental regions, with sub-ppb levels typical in more remote regions. Modeled annual mean surface [Cl] exhibits large spatial variability with the largest levels, typically in the range of 1–5 × 104 atoms cm−3, in the polluted northern hemisphere. Chlorocarbon oxidation provides a tropospheric Cly source of up to ~4320 Gg Cl/yr, sustaining a background surface [Cl] of <0.1 to 0.5 × 103 atoms cm−3 over large areas. Globally, we estimate a tropospheric methane sink of ~12–13 Tg CH4/yr due the CH4 + Cl reaction (~2.5% of total CH4 oxidation). Larger regional effects are predicted, with Cl accounting for ~10 to >20% of total boundary layer CH4 oxidation in some locations.

Photolysis of frozen iodate salts as a source of active iodine in the polar environment.

Oscar Gálvez, M. Teresa Baeza-Romero, Mikel Sanz and Alfonso Saiz-Lopez.

Atmos. Chem. Phys., 16, doi:10.5194/acp-16-12703-2016



Reactive halogens play a key role in the oxidation capacity of the polar troposphere. However, sources and mechanisms, particularly those involving active iodine, are still poorly understood. In this paper, the photolysis of an atmospherically relevant frozen iodate salt has been experimentally studied using infrared (IR) spectroscopy. The samples were generated at low temperatures in the presence of different amounts of water. The IR spectra have confirmed that, under near-ultraviolet–visible (UV–Vis) radiation, iodate is efficiently photolysed. The integrated IR absorption coefficient of the iodate anion on the band at 750 cm−1 has been measured to be A  =  9.8 ± 0.5  ×  10−17 cm molecule−1. The photolysis rate of the ammonium iodate salt was measured by monitoring the decay of ammonium or iodate IR bands (1430 and 750 cm−1 respectively) in the presence of a solar simulator. The absorption cross section of the liquid solutions of ammonium iodate at wavelengths relevant for the troposphere (250 to 400 nm) has been obtained and used to estimate the photolytic quantum yield for the frozen salt. Finally, using an atmospheric model, constrained with the experimental data, we suggest that the photolysis of iodate in frozen salt can potentially provide a pathway for the release of active iodine to the polar atmosphere.

MAX-DOAS retrieval of aerosol extinction properties in Madrid (Spain).

Shanshan Wang, Carlos A. Cuevas, Udo FrieB, and Alfonso Saiz-Lopez.

Atmos. Meas. Tech., 9, DOI:10.5194/amt-9-5089-2016



Multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements were performed in the urban environment of Madrid, Spain, from March to September 2015. The O4 absorption in the ultraviolet (UV) spectral region was used to retrieve the aerosol extinction profile using an inversion algorithm. The results show a good agreement between the hourly retrieved aerosol optical depth (AOD) and the correlative Aerosol Robotic Network (AERONET) product, with a correlation coefficient of R =  0.87. Higher AODs are found in the summer season due to the more frequent occurrence of Saharan dust intrusions. The surface aerosol extinction coefficient as retrieved by the MAX-DOAS measurements was also compared to in situ PM2.5 concentrations. The level of agreement between both measurements indicates that the MAX-DOAS retrieval has the ability to characterize the extinction of aerosol particles near the surface. The retrieval algorithm was also used to study a case of severe dust intrusion on 12 May 2015. The capability of the MAX-DOAS retrieval to recognize the dust event including an elevated particle layer is investigated along with air mass back-trajectory analysis.

The polar iodine paradox.

Alfonso Saiz-Lopez; Christopher Shawn Blaszczak-Boxe. J.

Atmos. Environ, 140, pp 72-73;, 2016



The uneven presence of iodine in the polar regions presents a scientific challenge, which connects marine algae, ice and atmosphere.

Global impacts of tropospheric halogens (Cl, Br, I) on oxidants and composition in GEOS-Chem.

Tomás Sherwen; Johan A. Schmidt; Mat J. Evans; Lucy J. Carpenter; Katja Großmann; Sebastian D. Eastham; Daniel J. Jacob; Barbara Dix; Theodore K. Koenig; Roman Sinreich, Ivan Ortega; Rainer Volkamer; Alfonso Saiz-Lopez; Cristina Prados-Roman; Anoop S. Mahajan; Carlos Ordóñez.

Atmos. Chem. Phys., 16, 12239-12271, DOI:10.5194/acp-16-12239-2016, 2016.



We present a simulation of the global present-day composition of the troposphere which includes the chemistry of halogens (Cl, Br, I). Building on previous work within the GEOS-Chem model we include emissions of inorganic iodine from the oceans, anthropogenic and biogenic sources of halogenated gases, gas phase chemistry, and a parameterised approach to heterogeneous halogen chemistry. Consistent with Schmidt et al. (2016) we do not include sea-salt debromination. Observations of halogen radicals (BrO, IO) are sparse but the model has some skill in reproducing these. Modelled IO shows both high and low biases when compared to different datasets, but BrO concentrations appear to be modelled low. Comparisons to the very sparse observations dataset of reactive Cl species suggest the model represents a lower limit of the impacts of these species, likely due to underestimates in emissions and therefore burdens. Inclusion of Cl, Br, and I results in a general improvement in simulation of ozone (O3) concentrations, except in polar regions where the model now underestimates O3 concentrations. Halogen chemistry reduces the global tropospheric O3 burden by 18.6 %, with the O3 lifetime reducing from 26 to 22 days. Global mean OH concentrations of 1.28  ×  106 molecules cm−3 are 8.2 % lower than in a simulation without halogens, leading to an increase in the CH4 lifetime (10.8 %) due to OH oxidation from 7.47 to 8.28 years. Oxidation of CH4 by Cl is small (∼  2 %) but Cl oxidation of other VOCs (ethane, acetone, and propane) can be significant (∼  15–27 %). Oxidation of VOCs by Br is smaller, representing 3.9 % of the loss of acetaldehyde and 0.9 % of the loss of formaldehyde.

On the variability of ozone in the equatorial eastern Pacific boundary layer.

J. C. Gómez Martín; H. Vömel; T. D. Hay; A. S. Mahajan; C. Ordóñez; M. C. Parrondo Sempere; M. Gil-Ojeda; A. Saiz-Lopez.

J. Geophys. Res. Atmos., 121, DOI:10.1002/2016JD025392 (2016)



Observations of surface ozone (O3) mixing ratios carried out during two ground-based field campaigns in the Galápagos Islands are reported. The first campaign, Primera Investigación sobre la Química, Evolución y Reparto de Ozono, was carried out from September 2000 to July 2002. The second study, Climate and HAlogen Reactivity tropicaL EXperiment, was conducted from September 2010 to March 2012. These measurements complement the Southern Hemisphere ADditional OZonesonde observations made with weekly to monthly frequency at Galápagos. In this work, the daily, intraseasonal, seasonal and interannual variability of O3 in the marine boundary layer are described and compared to those observed in other tropical locations. The O3 diurnal cycle shows two regimes: (i) photochemical destruction followed by nighttime recovery in the cold season (July to November) and (ii) daytime advection and photochemical loss followed by nighttime depositional loss associated to windless conditions in the warm season (February to April). Wavelet spectral analysis of the intraseasonal variability of O3 reveals components with periods characteristic of tropical instability waves. The O3 seasonal variation in Galápagos is typical of the Southern Hemisphere, with a maximum in August and a minimum in February–March. Comparison with other measurements in remote tropical ocean locations shows that the change of the surface O3 seasonal cycle across the equator is explained by the position of the Intertropical Convergence Zone and the O3 levels upwind.

Canadian Arctic sea ice reconstructed from bromine in the Greenland NEEM ice core.

Andrea Spolaor; Paul Vallelonga; Clara Turetta; Niccolò Maffezzoli; Giulio Cozzi; Jacopo Gabrieli; Carlo Barbante; Kumiko Goto-Azuma; Alfonso Saiz-Lopez; Carlos A. Cuevas; Dorthe Dahl-Jensen.

Sci. Rep. 6, 33925; DOI: 10.1038/srep33925 (2016)



Reconstructing the past variability of Arctic sea ice provides an essential context for recent multi-year sea ice decline, although few quantitative reconstructions cover the Holocene period prior to the earliest historical records 1,200 years ago. Photochemical recycling of bromine is observed over first-year, or seasonal, sea ice in so-called “bromine explosions” and we employ a 1-D chemistry transport model to quantify processes of bromine enrichment over first-year sea ice and depositional transport over multi-year sea ice and land ice. We report bromine enrichment in the Northwest Greenland Eemian NEEM ice core since the end of the Eemian interglacial 120,000 years ago, finding the maximum extension of first-year sea ice occurred approximately 9,000 years ago during the Holocene climate optimum, when Greenland temperatures were 2 to 3 °C above present values. First-year sea ice extent was lowest during the glacial stadials suggesting complete coverage of the Arctic Ocean by multi-year sea ice. These findings demonstrate a clear relationship between temperature and first-year sea ice extent in the Arctic and suggest multi-year sea ice will continue to decline as polar amplification drives Arctic temperatures beyond the 2 °C global average warming target of the recent COP21 Paris climate agreement.

A multi-model intercomparison of halogenated very short-lived substances (TransCom-VSLS): linking oceanic emissions and tropospheric transport for a reconciled estimate of the stratospheric source gas injection of bromine.

R. Hossaini, P. K. Patra, A. A. Leeson, G. Krysztofiak, N. L. Abraham, S. J. Andrews, A. T. Archibald, J. Aschmann, E. L. Atlas, D. A. Belikov, H. Bönisch, R. Butler, L. J. Carpenter, S. Dhomse, M. Dorf, A. Engel, L. Feng, W. Feng, S. Fuhlbrügge, P. T. Griffiths, N. R. P. Harris, R. Hommel, T. Keber, K. Krüger, S. T. Lennartz, S. Maksyutov, H. Mantle, G. P. Mills, B. Miller, S. A. Montzka, F. Moore, M. A. Navarro, D. E. Oram, P. I. Palmer, K. Pfeilsticker, J. A. Pyle, B. Quack, A. D. Robinson, E. Saikawa, A. Saiz-Lopez, S. Sala, B.-M. Sinnhuber, S. Taguchi, S. Tegtmeier, R. T. Lidster, C. Wilson, and F. Ziska.

Atmos. Chem. Phys., DOI:10.5194/acp-16-9163-2016



The first concerted multi-model intercomparison of halogenated very short-lived substances (VSLS) has been performed, within the framework of the ongoing Atmospheric Tracer Transport Model Intercomparison Project (TransCom). Eleven global models or model variants participated (nine chemical transport models and two chemistry–climate models) by simulating the major natural bromine VSLS, bromoform (CHBr3) and dibromomethane (CH2Br2), over a 20-year period (1993–2012). Except for three model simulations, all others were driven offline by (or nudged to) reanalysed meteorology. The overarching goal of TransCom-VSLS was to provide a reconciled model estimate of the stratospheric source gas injection (SGI) of bromine from these gases, to constrain the current measurement-derived range, and to investigate inter-model differences due to emissions and transport processes. Models ran with standardised idealised chemistry, to isolate differences due to transport, and we investigated the sensitivity of results to a range of VSLS emission inventories. Models were tested in their ability to reproduce the observed seasonal and spatial distribution of VSLS at the surface, using measurements from NOAA's long-term global monitoring network, and in the tropical troposphere, using recent aircraft measurements – including high-altitude observations from the NASA Global Hawk platform.

The models generally capture the observed seasonal cycle of surface CHBr3 and CH2Br2 well, with a strong model–measurement correlation (r  ≥  0.7) at most sites. In a given model, the absolute model–measurement agreement at the surface is highly sensitive to the choice of emissions. Large inter-model differences are apparent when using the same emission inventory, highlighting the challenges faced in evaluating such inventories at the global scale. Across the ensemble, most consistency is found within the tropics where most of the models (8 out of 11) achieve best agreement to surface CHBr3 observations using the lowest of the three CHBr3 emission inventories tested (similarly, 8 out of 11 models for CH2Br2). In general, the models reproduce observations of CHBr3 and CH2Br2 obtained in the tropical tropopause layer (TTL) at various locations throughout the Pacific well. Zonal variability in VSLS loading in the TTL is generally consistent among models, with CHBr3 (and to a lesser extent CH2Br2) most elevated over the tropical western Pacific during boreal winter. The models also indicate the Asian monsoon during boreal summer to be an important pathway for VSLS reaching the stratosphere, though the strength of this signal varies considerably among models.

We derive an ensemble climatological mean estimate of the stratospheric bromine SGI from CHBr3 and CH2Br2 of 2.0 (1.2–2.5) ppt,  ∼  57 % larger than the best estimate from the most recent World Meteorological Organization (WMO) Ozone Assessment Report. We find no evidence for a long-term, transport-driven trend in the stratospheric SGI of bromine over the simulation period. The transport-driven interannual variability in the annual mean bromine SGI is of the order of ±5 %, with SGI exhibiting a strong positive correlation with the El Niño–Southern Oscillation (ENSO) in the eastern Pacific. Overall, our results do not show systematic differences between models specific to the choice of reanalysis meteorology, rather clear differences are seen related to differences in the implementation of transport processes in the models.

An observationally constrained evaluation of the oxidative capacity in the tropical western Pacific troposphere

Julie M. Nicely, Daniel C. Anderson, Timothy P. Canty, Ross J. Salawitch, Glenn M. Wolfe, Eric C. Apel, Steve R. Arnold, Elliot L. Atlas, Nicola J. Blake, James F. Bresch, Teresa L. Campos, Russell R. Dickerson, Bryan Duncan, Louisa K. Emmons, Mathew J. Evans, Rafael P. Fernandez, Johannes Flemming, Samuel R. Hall, Thomas F. Hanisco, Shawn B. Honomichl, Rebecca S. Hornbrook, Vincent Huijnen, Lisa Kaser, Douglas E. Kinnison, Jean-Francois Lamarque, Jingqiu Mao, Sarah A. Monks, Denise D. Montzka, Laura L. Pan, Daniel D. Riemer, Alfonso Saiz-Lopez, Stephen D. Steenrod, Meghan H. Stell, Simone Tilmes, Solene Turquety, Kirk Ullmann, Andrew J. Weinheimer.

J. Geophys. Res. Atmos., 121, 7461–7488, DOI:10.1002/2016JD025067, 2016



Hydroxyl radical (OH) is the main daytime oxidant in the troposphere and determines the atmospheric lifetimes of many compounds. We use aircraft measurements of O3, H2O, NO, and other species from the Convective Transport of Active Species in the Tropics (CONTRAST) field campaign, which occurred in the tropical western Pacific (TWP) during January–February 2014, to constrain a photochemical box model and estimate concentrations of OH throughout the troposphere. We find that tropospheric column OH (OHCOL) inferred from CONTRAST observations is 12 to 40% higher than found in chemical transport models (CTMs), including CAM-chem-SD run with 2014 meteorology as well as eight models that participated in POLMIP (2008 meteorology). Part of this discrepancy is due to a clear-sky sampling bias that affects CONTRAST observations; accounting for this bias and also for a small difference in chemical mechanism results in our empirically based value of OHCOL being 0 to 20% larger than found within global models. While these global models simulate observed O3 reasonably well, they underestimate NOx (NO + NO2) by a factor of 2, resulting in OHCOL ~30% lower than box model simulations constrained by observed NO. Underestimations by CTMs of observed CH3CHO throughout the troposphere and of HCHO in the upper troposphere further contribute to differences between our constrained estimates of OH and those calculated by CTMs. Finally, our calculations do not support the prior suggestion of the existence of a tropospheric OH minimum in the TWP, because during January–February 2014 observed levels of O3 and NO were considerably larger than previously reported values in the TWP.

Evidence of atmospheric nanoparticle formation from emissions of marine microorganisms

K. Sellegri1, J. Pey; C. Rose; A. Culot; H. L. DeWitt; S. Mas; A. N. Schwier; B. Temime-Roussel; B. Charriere; A. Saiz-Lopez; A. S. Mahajan; D. Parin; A. Kukui;R. Sempere; B. D’Anna; N. Marchand.

Geophys. Res. Lett.,43, DOI: 10.1002/2016GL069389, 2016



Earth, as a whole, can be considered as a living organism emitting gases and particles into its atmosphere, in order to regulate its own temperature. In particular, oceans may respond to climate change by emitting particles that ultimately will influence cloud coverage. At the global scale, a large fraction of the aerosol number concentration is formed by nucleation of gas-phase species, but this process has never been directly observed above oceans. Here we present, using semicontrolled seawater-air enclosures, evidence that nucleation may occur from marine biological emissions in the atmosphere of the open ocean. We identify iodine-containing species as major precursors for new particle clusters' formation, while questioning the role of the commonly accepted dimethyl sulfide oxidation products, in forming new particle clusters in the region investigated and within a time scale on the order of an hour. We further show that amines would sustain the new particle formation process by growing the new clusters to larger sizes. Our results suggest that iodine-containing species and amines are correlated to different biological tracers. These observations, if generalized, would call for a substantial change of modeling approaches of the sea-to-air interactions.

On the formation of tropical rings of atomic halogens: Causes and implications

Alfonso Saiz-Lopez; Rafael P. Fernandez

Geophys. Res. Lett., 43, DOI:10.1002/2015GL067608, 2016



Halogens produced by ocean biological and photochemical processes reach the tropical tropopause layer (TTL), where cold temperatures and the prevailing low ozone abundances favor the diurnal photochemical enhancement of halogen atoms. Under these conditions atomic bromine and iodine are modeled to be the dominant inorganic halogen species in the sunlit TTL, surpassing the abundance of the commonly targeted IO and BrO radicals. We suggest that due to the rapid photochemical equilibrium between halogen oxides and halogen atoms a natural atmospheric phenomenon evolves, which we have collectively termed “tropical rings of atomic halogens.” We describe the main causes controlling the modeled appearance and variability of these superposed rings of bare bromine and iodine atoms that circle the tropics following the Sun. Some potential implications for atmospheric oxidizing capacity are also explored. Our model results suggest that if experimentally confirmed, the extent and intensity of the halogen rings would directly respond to changes in oceanic halocarbon emissions, their atmospheric transport, and photochemistry.

Iodine’s impact on tropospheric oxidants: a global model study in GEOS-Chem

T. Sherwen, M. J. Evans, L. J. Carpenter, S. J. Andrews, R. T. Lidster, B. Dix, T. K. Koenig, R. Sinreich, I. Ortega, R. Volkamer, A. Saiz-Lopez, C. Prados-Roman, A. S. Mahajan, and C. Ordóñez

Atmos. Chem. Phys., 16, 1161–1186, 2016, DOI:10.5194/acp-16-1161-2016



We present a global simulation of tropospheric iodine chemistry within the GEOS-Chem chemical transport model. This includes organic and inorganic iodine sources, standard gas-phase iodine chemistry, and simplified higher iodine oxide (I2OX, X  = 2, 3, 4) chemistry, photolysis, deposition, and parametrized heterogeneous reactions. In comparisons with recent iodine oxide (IO) observations, the simulation shows an average bias of  ∼ +90 % with available surface observations in the marine boundary layer (outside of polar regions), and of  ∼ +73 % within the free troposphere (350 hPa  <  p  <  900 hPa) over the eastern Pacific. Iodine emissions (3.8 Tg yr−1) are overwhelmingly dominated by the inorganic ocean source, with 76 % of this emission from hypoiodous acid (HOI). HOI is also found to be the dominant iodine species in terms of global tropospheric IY burden (contributing up to 70 %). The iodine chemistry leads to a significant global tropospheric O3 burden decrease (9.0 %) compared to standard GEOS-Chem (v9-2). The iodine-driven OX loss rate1 (748 Tg OX yr−1) is due to photolysis of HOI (78 %), photolysis of OIO (21 %), and reaction between IO and BrO (1 %). Increases in global mean OH concentrations (1.8 %) by increased conversion of hydroperoxy radicals exceeds the decrease in OH primary production from the reduced O3 concentration. We perform sensitivity studies on a range of parameters and conclude that the simulation is sensitive to choices in parametrization of heterogeneous uptake, ocean surface iodide, and I2OX (X  = 2, 3, 4) photolysis. The new iodine chemistry combines with previously implemented bromine chemistry to yield a total bromine- and iodine-driven tropospheric O3 burden decrease of 14.4 % compared to a simulation without iodine and bromine chemistry in the model, and a small increase in OH (1.8 %). This is a significant impact and so halogen chemistry needs to be considered in both climate and air quality models.

1 Here OX is defined as O3 + NO2 + 2NO3 + PAN + PMN+PPN + HNO4 + 3N2O5 + HNO3 + BrO + HOBr + BrNO2+2BrNO3 + MPN + IO + HOI + INO2 + 2INO3 + 2OIO+2I2O2 + 3I2O3 + 4I2O4, where PAN  =  peroxyacetyl nitrate, PPN  =  peroxypropionyl nitrate, MPN  =  methyl peroxy nitrate, and MPN  =  peroxymethacryloyl nitrate.

Halogen-based reconstruction of Russian Arctic sea ice area from the Akademii Nauk ice core (Severnaya Zemlya)

A. Spolaor; T. Opel; J. R. McConnell; O. J. Maselli; G. Spreen; C. Varin; T. Kirchgeorg; D. Fritzsche; A. Saiz-Lopez; P. Vallelonga.

The Cryosphere, 10, 245-256, DOI:10.5194/tc-10-245-2016, 2016.


The role of sea ice in the Earth climate system is still under debate, although it is known to influence albedo, ocean circulation, and atmosphere–ocean heat and gas exchange. Here we present a reconstruction of 1950 to 1998 AD sea ice in the Laptev Sea based on the Akademii Nauk ice core (Severnaya Zemlya, Russian Arctic). The chemistry of halogens bromine (Br) and iodine (I) is strongly active and influenced by sea ice dynamics, in terms of physical, chemical and biological process. Bromine reacts on the sea ice surface in autocatalyzing "bromine explosion" events, causing an enrichment of the Br / Na ratio and hence a bromine excess (Brexc) in snow compared to that in seawater. Iodine is suggested to be emitted from algal communities growing under sea ice. The results suggest a connection between Brexc and spring sea ice area, as well as a connection between iodine concentration and summer sea ice area. The correlation coefficients obtained between Brexc and spring sea ice (r  =  0.44) as well as between iodine and summer sea ice (r   =  0.50) for the Laptev Sea suggest that these two halogens could become good candidates for extended reconstructions of past sea ice changes in the Arctic.

A pervasive role for biomass burning in tropical high ozone/low water structures

Daniel C. Anderson; Julie M. Nicely; Ross J. Salawitch; Timothy P. Canty; Russell R. Dickerson; Thomas F. Hanisco; Glenn M. Wolfe; Eric C. Apel; Elliot Atlas; Thomas Bannan; Stephane Bauguitte; Nicola J. Blake; James F. Bresch; Teresa L. Campos; Lucy J. Carpenter; Mark D. Cohen; Mathew Evans; Rafael P. Fernandez; Brian H. Kahn; Douglas E. Kinnison; Samuel R. Hall; Neil R.P. Harris;Rebecca S. Hornbrook; Jean-Francois Lamarque; Michael Le Breton; James D. Lee; Carl Percival; Leonhard Pfister; R. Bradley Pierce; Daniel D. Riemer; Alfonso Saiz-Lopez; Barbara J.B. Stunder; Anne M. Thompson; Kirk Ullmann; Adam Vaughan; Andrew J. Weinheimer.

Nature Communications, 7, Article number: 10267. DOI: 10.1038/ncomms10267


Air parcels with mixing ratios of high O3 and low H2O (HOLW) are common features in the tropical western Pacific (TWP) mid-troposphere (300–700 hPa). Here, using data collected during aircraft sampling of the TWP in winter 2014, we find strong, positive correlations of O3 with multiple biomass burning tracers in these HOLW structures. Ozone levels in these structures are about a factor of three larger than background. Models, satellite data and aircraft observations are used to show fires in tropical Africa and Southeast Asia are the dominant source of high O3 and that low H2O results from large-scale descent within the tropical troposphere. Previous explanations that attribute HOLW structures to transport from the stratosphere or mid-latitude troposphere are inconsistent with our observations. This study suggest a larger role for biomass burning in the radiative forcing of climate in the remote TWP than is commonly appreciated.

Fuction of Molecular Iodine and Tri-iodide in the Frozen Solution of Iodide: Implication for Polar Atmosphere

Kitae Kim; Akihiro Yabushita; Masanori Okumura; Alfonso Saiz-Lopez; Carlos A. Cuevas; Christopher S. Blaszczak-Boxe; Dae Wi Min; Ho-Il Yoon; Wonyong Choi.

Environ. Sci. Technol., 2016, 50 (3), pp 1280–1287. DOI: 10.1021/acs.est.5b05148



The chemistry of reactive halogens in the polar atmosphere plays important roles in ozone and mercury depletion events, oxidizing capacity, and dimethylsulfide oxidation to form cloud-condensation nuclei. Among halogen species, the sources and emission mechanisms of inorganic iodine compounds in the polar boundary layer remain unknown. Here, we demonstrate that the production of tri-iodide (I3) via iodide oxidation, which is negligible in aqueous solution, is significantly accelerated in frozen solution, both in the presence and the absence of solar irradiation. Field experiments carried out in the Antarctic region (King George Island, 62°13′S, 58°47′W) also showed that the generation of tri-iodide via solar photo-oxidation was enhanced when iodide was added to various ice media. The emission of gaseous I2 from the irradiated frozen solution of iodide to the gas phase was detected by using cavity ring-down spectroscopy, which was observed both in the frozen state at 253 K and after thawing the ice at 298 K. The accelerated (photo-)oxidation of iodide and the subsequent formation of tri-iodide and I2 in ice appear to be related with the freeze concentration of iodide and dissolved O2 trapped in the ice crystal grain boundaries. We propose that an accelerated abiotic transformation of iodide to gaseous I2 in ice media provides a previously unrecognized formation pathway of active iodine species in the polar atmosphere.

Bimodal distribution of free tropospheric ozone over the tropical western Pacific revealed by airborne observations

L. L. Pan; S. B. Honomichl; W. J. Randel; E. C. Apel; E. L. Atlas; S. P. Beaton; J. F. Bresch; R. Hornbrook; D. E. Kinnison; J.-F. Lamarque; A. Saiz-Lopez; R. J. Salawitch; A. J. Weinheimer.

Geophysical Research Letters Volume 42, Issue 18 Pages 7844–7851. DOI: 10.1002/2015GL065562


A recent airborne field campaign over the remote western Pacific obtained the first intensive in situ ozone sampling over the warm pool region from oceanic surface to 15 km altitude (near 360 K potential temperature level). The new data set quantifies ozone in the tropical tropopause layer under significant influence of convective outflow. The analysis further reveals a bimodal distribution of free tropospheric ozone mixing ratio. A primary mode, narrowly distributed around 20 ppbv, dominates the troposphere from the surface to 15 km. A secondary mode, broadly distributed with a 60 ppbv modal value, is prominent between 3 and 8 km (320 K to 340 K potential temperature levels). The latter mode occurs as persistent layers of ozone-rich drier air and is characterized by relative humidity under 45%. Possible controlling mechanisms are discussed. These findings provide new insight into the physical interpretation of the “S”-shaped mean ozone profiles in the tropics.

Atmospheric ammonia and its impacts on regional air quality over the megacity of Shanghai, China

Shanshan Wang; Jialiang Nan; Chanzhen Shi; Qingyan Fu; Song Gao; Dongfang Wang; Huxiong Cui; Alfonso Saiz-Lopez; Bin Zhou.

Scientific Reports 5, Article number: 15842 (2015) doi:10.1038/srep15842


Atmospheric ammonia (NH3) has great environmental implications due to its important role in ecosystem and global nitrogen cycle, as well as contribution to secondary particle formation. Here, we report long-term continuous measurements of NH3 at different locations (i.e. urban, industrial and rural) in Shanghai, China, which provide an unprecedented portrait of temporal and spatial characteristics of atmospheric NH3 in and around this megacity. In addition to point emission sources, air masses originated from or that have passed over ammonia rich areas, e.g. rural and industrial sites, increase the observed NH3 concentrations inside the urban area of Shanghai. Remarkable high-frequency NH3 variations were measured at the industrial site, indicating instantaneous nearby industrial emission peaks. Additionally, we observed strong positive exponential correlations between NH4+/(NH4++NH3) and sulfate-nitrate-ammonium (SNA) aerosols, PM2.5 mass concentrations, implying a considerable contribution of gas-to-particle conversion of ammonia to SNA aerosol formation. Lower temperature and higher humidity conditions were found to favor the conversion of gaseous ammonia to particle ammonium, particularly in autumn. Although NH3 is currently not included in China’s emission control policies of air pollution precursors, our results highlight the urgency and importance of monitoring gaseous ammonia and improving its emission inventory in and around Shanghai.

On the concentration and size distribution of sub-micron aerosol in the Galápagos Islands

M. Sorribas, J.C. Gómez Martín; T.D. Hay; A.S. Mahajan; C.A. Cuevas; M.V. Agama Reyes; Paredes Mora; M. Gil-Ojeda; A. Saiz-Lopez.

Atmospheric Environment Volume 123, Part A, December 2015, Pages 39–48 doi:10.1016/j.atmosenv.2015.10.028


During the CHARLEX campaign in the Galápagos Islands, a Scanning Particle Mobility Sizer was deployed on San Cristobal Island in July–August 2011 to carry out size-resolved measurements of the concentration of submicron aerosols. To our knowledge these are the first measurements of aerosol concentrations in this unique environment. The particles with marine origin displayed a tri-modal number size distribution with peak diameters of 0.016 μm, 0.050 μm and 0.174 μm and a cloud-processed intermodal minimum at 0.093 μm. The mean total aerosol number concentration for the marine contribution was 470 ± 160 cm−3. A low particle concentration of 70 ± 50 cm−3 for the nucleation size range was measured, but no evidence of new particle production in the atmospheric marine boundary layer (MBL) was observed. The concentration of the Aitken size mode was found to be related to aerosol entrainment from the free troposphere off the coast of Chile followed by transport within the MBL to the Galápagos Islands. Cloud processing may activate the particles in the Aitken size range, growing through ‘in-cloud’ sulphate production and increasing the particle concentration in the accumulation size range. The 0.093 μm cloud processed minima suggests that the critical supersaturation at which the particle is activated to a cloud droplet is in the 0.14–0.21% range. The daytime marine particle background concentration was influenced by human activity around the sampling site, as well as by new particle formation triggered by biogenic emissions from the vegetation cover of the island's semiarid lowlands. Effective CCN formation may play a role in the formation and properties of the stratus clouds, which permanently cover the top of the windward side of the islands and establish one of their characteristic climatic bands.

Airborne measurements of organic bromine compounds in the Pacific tropical tropopause layer

Maria A. Navarro; Elliot L. Atlasa; Alfonso Saiz-Lopez; Xavier Rodriguez-Lloveras; Douglas E. Kinnison; Jean-Francois Lamarque; Simone Tilmes; Michal Filus; Neil R. P. Harris; Elena Meneguz; Matthew J. Ashfold; Alistair J. Manning; Carlos A. Cuevas; Sue M. Schauffler; and Valeria Donets.

PNAS November 10, 2015 vol. 112 no. 45 13789-13793,


Very short-lived brominated substances (VSLBr) are an important source of stratospheric bromine, an effective ozone destruction catalyst. However, the accurate estimation of the organic and inorganic partitioning of bromine and the input to the stratosphere remains uncertain. Here, we report near-tropopause measurements of organic brominated substances found over the tropical Pacific during the NASA Airborne Tropical Tropopause Experiment campaigns. We combine aircraft observations and a chemistry−climate model to quantify the total bromine loading injected to the stratosphere. Surprisingly, despite differences in vertical transport between the Eastern and Western Pacific, VSLBr (organic + inorganic) contribute approximately similar amounts of bromine [∼6 (4−9) parts per thousand] to the stratospheric input at the tropical tropopause. These levels of bromine cause substantial ozone depletion in the lower stratosphere, and any increases in future abundances (e.g., as a result of aquaculture) will lead to larger depletions.


A nocturnal atmospheric loss of CH2I2 in the remote marine boundary layer

Lucy J. Carpenter; Stephen J. Andrews; Richard T. Lidster; Alfonso Saiz-Lopez; Miguel Fernandez-Sanchez; William J. Bloss; Bin Ouyang; Roderic L. Jones.

J Atmos Chem., 1-12, 10.1007/s10874-015-9320-6


Ocean emissions of inorganic and organic iodine compounds drive the biogeochemical cycle of iodine and produce reactive ozone-destroying iodine radicals that influence the oxidizing capacity of the atmosphere. Di-iodomethane (CH2I2) and chloro-iodomethane (CH2ICl) are the two most important organic iodine precursors in the marine boundary layer. Ship-borne measurements made during the TORERO (Tropical Ocean tRoposphere Exchange of Reactive halogens and Oxygenated VOC) field campaign in the east tropical Pacific Ocean in January/February 2012 revealed strong diurnal cycles of CH2I2 and CH2ICl in air and of CH2I2 in seawater. Both compounds are known to undergo rapid photolysis during the day, but models assume no night-time atmospheric losses. Surprisingly, the diurnal cycle of CH2I2 was lower in amplitude than that of CH2ICl, despite its faster photolysis rate. We speculate that night-time loss of CH2I2 occurs due to reaction with NO3 radicals. Indirect results from a laboratory study under ambient atmospheric boundary layer conditions indicate a k CH2I2+NO3 of ≤4 × 10−13 cm3 molecule−1 s−1; a previous kinetic study carried out at ≤100 Torr found k CH2I2+NO3 of 4 × 10−13 cm3 molecule−1 s−1. Using the 1-dimensional atmospheric THAMO model driven by sea-air fluxes calculated from the seawater and air measurements (averaging 1.8 +/− 0.8 nmol m−2 d−1 for CH2I2 and 3.7 +/− 0.8 nmol m−2 d−1 for CH2ICl), we show that the model overestimates night-time CH2I2 by >60 % but reaches good agreement with the measurements when the CH2I2 + NO3 reaction is included at 2–4 × 10−13 cm3 molecule−1 s−1. We conclude that the reaction has a significant effect on CH2I2 and helps reconcile observed and modeled concentrations. We recommend further direct measurements of this reaction under atmospheric conditions, including of product branching ratios.

NO2 seasonal evolution in the subtropical free troposphere

M. Gil-Ojeda, M. Navarro-Comas, L. Gómez-Martin, J.A. Adame, A. Saiz-Lopez, C.A. Cuevas, Y. González, O. Puentedura, E. Cuevas, J.-F. Lamarque, D. Kinnison, and S. Tilmes

Atmos. Chem. Phys., 15, 10567-10579, 2015

Abstract:three years of multi-axis differential optical absorption spectroscopy (MAXDOAS) measurements (2011–2013) have been used for estimating the NO2 mixing ratio along a horizontal line of sight from the high mountain subtropical observatory of Izaña, at 2370 m a.s.l. (NDACC station, 28.3° N, 16.5° W). The method is based on horizontal path calculation from the O2–O2 collisional complex at the 477 nm absorption band which is measured simultaneously to the NO2 column density, and is applicable under low aerosol-loading conditions.

The MAXDOAS technique, applied in horizontal mode in the free troposphere, minimizes the impact of the NO2 contamination resulting from the arrival of marine boundary layer (MBL) air masses from thermally forced upwelling breeze during middle hours of the day. Comparisons with in situ observations show that during most of the measuring period, the MAXDOAS is insensitive or very slightly sensitive to the upwelling breeze. Exceptions are found for pollution events during southern wind conditions. On these occasions, evidence of fast, efficient and irreversible transport from the surface to the free troposphere is found.

Background NO2 volume mixing ratio (vmr), representative of the remote free troposphere, is in the range of 20–45 pptv. The observed seasonal evolution shows an annual wave where the peak is in phase with the solar radiation. Model simulations with the chemistry–climate CAM-Chem model are in good agreement with the NO2 measurements, and are used to further investigate the possible drivers of the NO2 seasonality observed at Izaña.

Injection of iodine to the stratosphere

A. Saiz-Lopez, S. Baidar, C.A. Cuevas, T.K. Koening, R.P. Fernandez, B. Dix, D.E. Kinnison, J.-F. Lamarque, X. Rodriguez-Lloveras, T.L. Campos, R. Volkamer

Geophys. Res. Lett., 42, doi:10.1002/2015GL064796

Abstract: We report a new estimation of the injection of iodine into the stratosphere based on novel daytime (solar zenith angle < 45°) aircraft observations in the tropical tropopause layer and a global atmospheric model with the most recent knowledge about iodine photochemistry. The results indicate that significant levels of total reactive iodine (0.25–0.7 parts per trillion by volume), between 2 and 5 times larger than the accepted upper limits, can be injected into the stratosphere via tropical convective outflow. At these iodine levels, modeled iodine catalytic cycles account for up to 30% of the contemporary ozone loss in the tropical lower stratosphere and can exert a stratospheric ozone depletion potential equivalent to, or even larger than, that of very short-lived bromocarbons. Therefore, we suggest that iodine sources and chemistry need to be considered in assessments of the historical and future evolution of the stratospheric ozone layer.

A mechanism for biologically induced iodine emissions from sea ice

A. Saiz-Lopez, C.S. Blaszczak-Boxe and L.J. Carpenter

Atmos. Chem. Phys., 15, 9731-9746, 2015

Abstract: Ground- and satellite-based measurements have reported high concentrations of iodine monoxide (IO) in coastal Antarctica. The sources of such a large iodine burden in the coastal Antarctic atmosphere remain unknown. We propose a mechanism for iodine release from sea ice based on the premise that micro-algae are the primary source of iodine emissions in this environment. The emissions are triggered by the biological production of iodide (I) and hypoiodous acid (HOI) from micro-algae (contained within and underneath sea ice) and their diffusion through sea-ice brine channels, ultimately accumulating in a thin brine layer (BL) on the surface of sea ice. Prior to reaching the BL, the diffusion timescale of iodine within sea ice is depth-dependent. The BL is also a vital component of the proposed mechanism as it enhances the chemical kinetics of iodine-related reactions, which allows for the efficient release of iodine to the polar boundary layer. We suggest that iodine is released to the atmosphere via three possible pathways: (1) emitted from the BL and then transported throughout snow atop sea ice, from where it is released to the atmosphere; (2) released directly from the BL to the atmosphere in regions of sea ice that are not covered with snowpack; or (3) emitted to the atmosphere directly through fractures in the sea-ice pack. To investigate the proposed biology–ice–atmosphere coupling at coastal Antarctica we use a multiphase model that incorporates the transport of iodine species, via diffusion, at variable depths, within brine channels of sea ice. Model simulations were conducted to interpret observations of elevated springtime IO in the coastal Antarctic, around the Weddell Sea. While a lack of experimental and observational data adds uncertainty to the model predictions, the results nevertheless show that the levels of inorganic iodine (i.e. I2, IBr, ICl) released from sea ice through this mechanism could account for the observed IO concentrations during this timeframe. The model results also indicate that iodine may trigger the catalytic release of bromine from sea ice through phase equilibration of IBr. Considering the extent of sea ice around the Antarctic continent, we suggest that the resulting high levels of iodine may have widespread impacts on catalytic ozone destruction and aerosol formation in the Antarctic lower troposphere.

Particles and iodine compounds in coastal Antarctica

Howard K. Roscoe, Anna E. Jones, Neil Brough, Rolf Weller, Alfonso Saiz-Lopez, Anoop S. Mahajan, Anja Schönhardt, John P. Burrows and Zoe L. Fleming

J. Geophys. Res. Atmos., 120, doi:10.1002/2015JD023301

Abstract. Aerosol particle number concentrations have been measured at Halley and Neumayer on the Antarctic coast, since 2004 and 1984, respectively. Sulphur compounds known to be implicated in particle formation and growth were independently measured: sulphate ions and methane sulphonic acid in filtered aerosol samples and gas phase dimethyl sulphide for limited periods. Iodine oxide, IO, was determined by a satellite sensor from 2003 to 2009 and by different ground-based sensors at Halley in 2004 and 2007. Previous model results and midlatitude observations show that iodine compounds consistent with the large values of IO observed may be responsible for an increase in number concentrations of small particles. Coastal Antarctica is useful for investigating correlations between particles, sulphur, and iodine compounds, because of their large annual cycles and the source of iodine compounds in sea ice. After smoothing all the measured data by several days, the shapes of the annual cycles in particle concentration at Halley and Neumayer are approximated by linear combinations of the shapes of sulphur compounds and IO but not by sulphur compounds alone. However, there is no short-term correlation between IO and particle concentration. The apparent correlation by eye after smoothing but not in the short term suggests that iodine compounds and particles are sourced some distance offshore. This suggests that new particles formed from iodine compounds are viable, i.e., they can last long enough to grow to the larger particles that contribute to cloud condensation nuclei, rather than being simply collected by existing particles. If so, there is significant potential for climate feedback near the sea ice zone via the aerosol indirect effect.

Impact of Enhanced Ozone Deposition and Halogen Chemistry on Tropospheric Ozone over the Northen Hemisphere

Golam Sarwar, Brett Gantt, Donna Schewede, Kristen Foley, Robit Mathur and Alfonso Saiz-Lopez

Environ. Sci. Technol. DOI_10.1021/acs.est.5b01657

Abstract. Fate of ozone in marine environments has been receiving increased attention due to the tightening of ambient air quality standards. The role of deposition and halogen chemistry is examined through incorporation of an enhanced ozone deposition algorithm and inclusion of halogen chemistry in a comprehensive atmospheric modeling system. The enhanced ozone deposition treatment accounts for the interaction of iodide in seawater with ozone and increases deposition velocities by 1 order of magnitude. Halogen chemistry includes detailed chemical reactions of organic and inorganic bromine and iodine species. Two different simulations are completed with the halogen chemistry: without and with photochemical reactions of higher iodine oxides. Enhanced deposition reduces mean summer-time surface ozone by ∼3% over marine regions in the Northern Hemisphere. Halogen chemistry without the photochemical reactions of higher iodine oxides reduces surface ozone by ∼15% whereas simulations with the photochemical reactions of higher iodine oxides indicate ozone reductions of ∼48%. The model without these processes overpredicts ozone compared to observations whereas the inclusion of these processes improves predictions. The inclusion of photochemical reactions for higher iodine oxides leads to ozone predictions that are lower than observations, underscoring the need for further refinement of the halogen emissions and chemistry scheme in the model.

Growth in stratospheric chlorine from short-lived chemicals not controlled by the Montreal Protocol

R. Hossaini, M.P. Chipperfield, A. Saiz-Lopez, J.J. Harrison, R. von Glasow, R. Sommariva, E. Atlas, M. Navarro, S.A. Montzka, W. Feng, S. Dhomse, C. Harth, J. Mühle, C. Lunder, S. O'Doherty, D. Young, S. Reimann, M.K. Vollmer, P.B. Krummel, P.F. Bernath.

Geophys. Res. Lett., 42, doi:10.1002/2015GL063783.

Abstract. We have developed a chemical mechanism describing the tropospheric degradation of chlorine containing very short-lived substances (VSLS). The scheme was included in a global atmospheric model and used to quantify the stratospheric injection of chlorine from anthropogenic VSLS (ClyVSLS) between 2005 and 2013. By constraining the model with surface measurements of chloroform (CHCl3), dichloromethane (CH2Cl2), tetrachloroethene (C2Cl4), trichloroethene (C2HCl3), and 1,2-dichloroethane (CH2ClCH2Cl), we infer a 2013 (ClyVSLS) mixing ratio of 123 parts per trillion (ppt). Stratospheric injection of source gases dominates this supply, accounting for ∼83% of the total. The remainder comes from VSLS-derived organic products, phosgene (COCl2, 7%) and formyl chloride (CHClO, 2%), and also hydrogen chloride (HCl, 8%). Stratospheric (ClyVSLS)  increased by ∼52% between 2005 and 2013, with a mean growth rate of 3.7 ppt Cl/yr. This increase is due to recent and ongoing growth in anthropogenic CH2Cl2—the most abundant chlorinated VSLS not controlled by the Montreal Protocol.

Quantifying the impacts of an updated global dimethyl sulfide climatology on cloud microphysics and aerosol radiative forcing

Anoop S. Mahajan, Suvarna Fadnavis, Manu A. Thomas, Luca Pozzoli, Smrati Gupta, Sarah-Jeanne Royer, Alfonso Saiz-Lopez, Rafel Simó.

J. Geophys. Res. 120, 6, 2524-2536. DOI: 10.1002/2014JD022687

Abstract. One of the critical parameters in assessing the global impacts of dimethyl sulfide (DMS) on cloud properties and the radiation budget is the estimation of phytoplankton-induced ocean emissions, which are derived from prescribed, climatological surface seawater DMS concentrations. The most widely used global ocean DMS climatology was published 15 years ago and has recently been updated using a much larger database of observations. The updated climatology displays significant differences in terms of the global distribution and regional monthly averages of sea surface DMS. In this study, we use the ECHAM5-HAMMOZ aerosol-chemistry-climate general circulation model to quantify the influence of the updated DMS climatology in computed atmospheric properties, namely, the spatial and temporal distributions of atmospheric DMS concentration, sulfuric acid concentration, sulfate aerosols, number of activated aerosols, cloud droplet number concentration, and the aerosol radiative forcing at the top of the atmosphere. Significant differences are observed for all the modeled variables. Comparison with observations of atmospheric DMS and total sulfate also shows that in places with large DMS emissions, the updated climatology shows a better match with the observations. This highlights the importance of using the updated climatology for projecting future impacts of oceanic DMS emissions, especially considering that the relative importance of the natural sulfur fluxes is likely to increase due to legislation to “clean up” anthropogenic emissions. The largest estimated differences are in the Southern Ocean, Indian Ocean, and parts of the Pacific Ocean, where the climatologies differ in seasonal concentrations over large geographical areas. The model results also indicate that the former DMS climatology underestimated the effect of DMS on the globally averaged annual aerosol radiative forcing at the top of the atmosphere by about 20%.

Tropospheric Halogen Chemistry: Sources, Cycling, and Impacts

William R. Simpson, Steven S. Brown, Alfonso Saiz-Lopez, Joel A. Thornton, and Roland von Glasow

Chem. Rev., Article. DOI: 10.1021/cr5006638

A negative feedback between anthropogenic ozone pollution and enhanced ocean emissions of iodine

C. Prados-Roman, C.A. Cuevas, R.P. Fernandez, D.E. Kinnison, J.-F. Lamarque, and A. Saiz-Lopez

Atmos. Chem. Phys., 15, 2215-2224, 2015

Abstract. Naturally emitted from the oceans, iodine compounds efficiently destroy atmospheric ozone and reduce its positive radiative forcing effects in the troposphere. Emissions of inorganic iodine have been experimentally shown to depend on the deposition to the oceans of tropospheric ozone, whose concentrations have significantly increased since 1850 as a result of human activities. A chemistry–climate model is used herein to quantify the current ocean emissions of inorganic iodine and assess the impact that the anthropogenic increase in tropospheric ozone has had on the natural cycle of iodine in the marine environment since pre-industrial times. Our results indicate that the human-driven enhancement of tropospheric ozone has doubled the oceanic inorganic iodine emissions following the reaction of ozone with iodide at the sea surface. The consequent build-up of atmospheric iodine, with maximum enhancements of up to 70% with respect to pre-industrial times in continental pollution outflow regions, has in turn accelerated the ozone chemical loss over the oceans with strong spatial patterns. We suggest that this ocean–atmosphere interaction represents a negative geochemical feedback loop by which current ocean emissions of iodine act as a natural buffer for ozone pollution and its radiative forcing in the global marine environment.

Iodine oxide in the global marine boundary layer

C. Prados-Roman, C.A. Cuevas, T. Hay, R.P. Fernandez, A.S. Mahajan, S.-J. Royer, M. Gali, R. Simó, J. Dachs, K. Groβmann, D.E. Kinnison, J.-F. Lamarque, and A. Saiz-Lopez

Atmos. Chem. Phys., 15, 583-593, 2015

Abstract. Emitted mainly by the oceans, iodine is a halogen compound important for atmospheric chemistry due to its high ozone depletion potential and effect on the oxidizing capacity of the atmosphere. Here we present a comprehensive dataset of iodine oxide (IO) measurements in the open marine boundary layer (MBL) made during the Malaspina 2010 circumnavigation. Results show IO mixing ratios ranging from 0.4 to 1 pmol mol−1 and, complemented with additional field campaigns, this dataset confirms through observations the ubiquitous presence of reactive iodine chemistry in the global marine environment. We use a global model with organic (CH3I, CH2ICl, CH2I2 and CH2IBr) and inorganic (HOI and I2) iodine ocean emissions to investigate the contribution of the different iodine source gases to the budget of IO in the global MBL. In agreement with previous estimates, our results indicate that, globally averaged, the abiotic precursors contribute about 75% to the iodine oxide budget. However, this work reveals a strong geographical pattern in the contribution of organic vs. inorganic precursors to reactive iodine in the global MBL.

Perspectives and Integration in SOLAS Science

Véronique C. Garçon, Thomas G. Bell,  Wallace, R. Arnold, Alex Baker, Dorothee C. E. Bakker, Hermann W. Bange, Nicholas R. Bates, Laurent Bopp, Jacqueline Boutin, Philip W. Boyd, Astrid Bracher, John P. Burrows, Lucy J. Carpenter, Gerrit de Leeuw, Katja Fennel, Jordi Font, Tobias Friedrich, Christoph S. Garbe, Nicolas Gruber, Lyatt Jaegl, éArancha Lana, James D. Lee, Peter S. Liss, Lisa A. Miller, Nazli Olgun, Are Olsen, Benjamin Pfeil, Birgit Quack, Katie A. Read, Nicolas Reul, Christian Rödenbeck, Shital S. Rohekar, Alfonso Saiz-Lopez, Eric S. Saltzman, Oliver Schneising, Ute Schuster, Roland Seferian, Tobias Steinhoff, Pierre-Yves Le Traon, Franziska Ziska

Ocean-Atmosphere Interactions of Gases and Particles pp 247-306



Why a chapter on Perspectives and Integration in SOLAS Science in this book? SOLAS science by its nature deals with interactions that occur: across a wide spectrum of time and space scales, involve gases and particles, between the ocean and the atmosphere, across many disciplines including chemistry, biology, optics, physics, mathematics, computing, socio-economics and consequently interactions between many different scientists and across scientific generations. This chapter provides a guide through the remarkable diversity of cross-cutting approaches and tools in the gigantic puzzle of the SOLAS realm.

Here we overview the existing prime components of atmospheric and oceanic observing systems, with the acquisition of ocean–atmosphere observables either from in situ or from satellites, the rich hierarchy of models to test our knowledge of Earth System functioning, and the tremendous efforts accomplished over the last decade within the COST Action 735 and SOLAS Integration project frameworks to understand, as best we can, the current physical and biogeochemical state of the atmosphere and ocean commons. A few SOLAS integrative studies illustrate the full meaning of interactions, paving the way for even tighter connections between thematic fields. Ultimately, SOLAS research will also develop with an enhanced consideration of societal demand while preserving fundamental research coherency.

The exchange of energy, gases and particles across the air-sea interface is controlled by a variety of biological, chemical and physical processes that operate across broad spatial and temporal scales. These processes influence the composition, biogeochemical and chemical properties of both the oceanic and atmospheric boundary layers and ultimately shape the Earth system response to climate and environmental change, as detailed in the previous four chapters. In this cross-cutting chapter we present some of the SOLAS achievements over the last decade in terms of integration, upscaling observational information from process-oriented studies and expeditionary research with key tools such as remote sensing and modelling.

Here we do not pretend to encompass the entire legacy of SOLAS efforts but rather offer a selective view of some of the major integrative SOLAS studies that combined available pieces of the immense jigsaw puzzle. These include, for instance, COST efforts to build up global climatologies of SOLAS relevant parameters such as dimethyl sulphide, interconnection between volcanic ash and ecosystem response in the eastern subarctic North Pacific, optimal strategy to derive basin-scale CO2 uptake with good precision, or significant reduction of the uncertainties in sea-salt aerosol source functions. Predicting the future trajectory of Earth’s climate and habitability is the main task ahead. Some possible routes for the SOLAS scientific community to reach this overarching goal conclude the chapter.


New insights into martian atmospheric chemistry

C.S. Boxe, J.S. Francisco, R.-L. Shia, Y.L. Yung, H. Nair, M.-C. Liang, A. Saiz-Lopez

Icarus 242 (2014) 97-104

Abstract. HOx radicals are produced in the martian atmosphere by the photolysis of water vapor and subsequently participate in catalytic cycles that recycle carbon dioxide (CO2) from its photolysis product carbon monoxide (CO), providing a qualitative explanation for the stability of its atmosphere. Balancing CO2 production and loss based on our current understanding of martian gas-phase chemistry has, however, proven to be difficult. The photolysis of O3 produces O(1D), while oxidation of CO produces HOCO radicals, a new member of the HOx family. The O(1D) quantum yield has recently been updated, which quantifies nonzero quantum yields in the Huggins bands. In Earth’s atmosphere HOCO is considered to be unimportant since it is quickly removed by abundant oxygen molecules. The smaller amount of O2 in the Mars’ atmosphere causes HOCO’s lifetime to be longer in Mars’ atmosphere than Earth’s (3 × 10−5 s to 1.2 days from Mars’s surface to 240 km, respectively). Limited kinetic data on reactions involving HOCO prevented consideration of its reactions directly in atmospheric models. Therefore, the impact of HOCO reactions on martian chemistry is currently unknown. Here, we incorporate new literature rate constants for HOCO chemistry and an updated representation of the O(1D) quantum yield in the Caltech/JPL 1-D photochemical model for Mars’ atmosphere. Our simulations exemplify perturbations to NOy, HOx, and COx species, ranging from 5% to 50%. The modified O(1D) quantum yield and new HOCO chemistry cause a 10% decrease and a 50% increase in OH and H2O2 total column abundances, respectively. At low altitudes, HOCO production contributes 5% towards CO2 production. Given recent experimentally-obtained branching ratios for the oxidation of CO, HOCO may contribute up to 70% toward the production of NOy, where HOx and NOy species are enhanced up to a factor 3, which has implications for rethinking the fundamental understanding of NOy, HOx, and CO/CO2 cycling on Mars. Two new reaction mechanisms for converting CO to CO2 using HOCO reactions are proposed, which reveal that H2O2 is more intimately coupled to COx chemistry. Our simulations are in good agreement with satellite/spacecraft measurements of CO and H2O2 on Mars.

Iodine chemistry in the troposphere and its effect on ozone

A. Saiz-Lopez, R.P. Fernandez, C. Ordoñez, D.E. Kinnison, J.C. Gómez Martín, J.-F. Lamarque and S. Tilmes.

Atmos. Chem. Phys., 14, 13119-13143, 2014

Abstract. Despite the potential influence of iodine chemistry on the oxidizing capacity of the troposphere, reactive iodine distributions and their impact on tropospheric ozone remain almost unexplored aspects of the global atmosphere. Here we present a comprehensive global modelling experiment aimed at estimating lower and upper limits of the inorganic iodine burden and its impact on tropospheric ozone. Two sets of simulations without and with the photolysis of IxOy oxides (i.e. I2O2, I2O3 and I2O4) were conducted to define the range of inorganic iodine loading, partitioning and impact in the troposphere. Our results show that the most abundant daytime iodine species throughout the middle to upper troposphere is atomic iodine, with an annual average tropical abundance of (0.15–0.55) pptv. We propose the existence of a "tropical ring of atomic iodine" that peaks in the tropical upper troposphere (~11–14 km) at the equator and extends to the sub-tropics (30° N–30° S). Annual average daytime I / IO ratios larger than 3 are modelled within the tropics, reaching ratios up to ~20 during vigorous uplift events within strong convective regions. We calculate that the integrated contribution of catalytic iodine reactions to the total rate of tropospheric ozone loss (IOx Loss) is 2–5 times larger than the combined bromine and chlorine cycles. When IxOy photolysis is included, IOx Loss represents an upper limit of approximately 27, 14 and 27% of the tropical annual ozone loss for the marine boundary layer (MBL), free troposphere (FT) and upper troposphere (UT), respectively, while the lower limit throughout the tropical troposphere is ~9%. Our results indicate that iodine is the second strongest ozone-depleting family throughout the global marine UT and in the tropical MBL. We suggest that (i) iodine sources and its chemistry need to be included in global tropospheric chemistry models, (ii) experimental programs designed to quantify the iodine budget in the troposphere should include a strategy for the measurement of atomic I, and (iii) laboratory programs are needed to characterize the photochemistry of higher iodine oxides to determine their atmospheric fate since they can potentially dominate halogen-catalysed ozone destruction in the troposphere.

Bromine partitioning in the tropical tropopause layer: implications for stratospheric injection

R.P. Fernandez, R.J. Salawitch, D.E. Kinnison, J.-F. Lamarque and A. Saiz-Lopez

Atmos. Chem. Phys., 14, 13391-13410, 2014

Abstract. Very short-lived (VSL) bromocarbons are produced at a prodigious rate by ocean biology and these source compounds (SGVSL), together with their inorganic degradation products (PGVSL), are lofted by vigorous convection to the tropical tropopause layer (TTL). Using a state-of-the-art photochemical mechanism within a global model, we calculate annual average stratospheric injection of total bromine due to VSL sources to be 5 pptv (parts per trillion by volume), with ~ 3 pptv entering the stratosphere as PGVSL and ~ 2 pptv as SGVSL. The geographic distribution and partitioning of VSL bromine within the TTL, and its consequent stratospheric injection, is highly dependent on the oceanic flux, the strength of convection and the occurrence of heterogeneous recycling reactions. Our calculations indicate atomic Br should be the dominant inorganic species in large regions of the TTL during daytime, due to the low ozone and cold conditions of this region. We propose the existence of a "tropical ring of atomic bromine" located approximately between 15 and 19 km and between 30° N and 30° S. Daytime Br / BrO ratios of up to ~ 4 are predicted within this inhomogeneous ring in regions of highly convective transport, such as the tropical Western Pacific. Therefore, we suggest that experimental programs designed to quantify the bromine budget of the TTL and the stratospheric injection of VSL biogenic bromocarbons should include a strategy for the measurement of atomic Br during daytime as well as HOBr and BrCl during nighttime.

Evolution of NO2 levels in Spain from 1996 to 2012

C.A. Cuevas, A. Notario, J.A. Adame, A. Hilboll, A. Richter, J.P. Burrows and A. Saiz-Lopez

Sci. Rep. 4, 5887; DOI:10.1038/srep05887 (2014).

Abstract. We report on the evolution of tropospheric nitrogen dioxide (NO2) over Spain, focusing on the densely populated cities of Barcelona, Bilbao, Madrid, Sevilla and Valencia, during 17 years, from 1996 to 2012. This data series combines observations from in-situ air quality monitoring networks and the satellite-based instruments GOME and SCIAMACHY. The results in these five cities show a smooth decrease in the NO2 concentrations of ~2% per year in the period 1996–2008, due to the implementation of emissions control environmental legislation, and a more abrupt descend of ~7% per year from 2008 to 2012 as a consequence of the economic recession. In the whole Spanish territory the NO2 levels have decreased by ~22% from 1996 to 2012. Statistical analysis of several economic indicators is used to investigate the different factors driving the NO2 concentration trends over Spain during the last two decades.

A laboratory characterisation of inorganic iodine emissions from the sea surface: dependence on oceanic variables and parameterisation for global modelling

S.M. MacDonald, J.C. Gómez Martín, R. Chance, S.Warriner, A. Saiz-Lopez, L.J. Carpenter, and J.M.C. Plane

Atmos. Chem. Phys., 14, 5841-5852, 2014

Abstract. Reactive iodine compounds play a significant role in the atmospheric chemistry of the oceanic boundary layer by influencing the oxidising capacity through catalytically removing O3 and altering the HOx and NOx balance. The sea-to-air flux of iodine over the open ocean is therefore an important quantity in assessing these impacts on a global scale. This paper examines the effect of a number of relevant environmental parameters, including water temperature, salinity and organic compounds, on the magnitude of the HOI and I2 fluxes produced from the uptake of O3 and its reaction with iodide ions in aqueous solution. The results of these laboratory experiments and those reported previously (Carpenter et al., 2013), along with sea surface iodide concentrations measured or inferred from measurements of dissolved total iodine and iodate reported in the literature, were then used to produce parameterised expressions for the HOI and I2 fluxes as a function of wind speed, sea-surface temperature and O3. These expressions were used in the Tropospheric HAlogen chemistry MOdel (THAMO) to compare with MAX-DOAS measurements of iodine monoxide (IO) performed during the HaloCAST-P cruise in the eastern Pacific ocean (Mahajan et al., 2012). The modelled IO agrees reasonably with the field observations, although significant discrepancies are found during a period of low wind speeds (< 3 m s−1), when the model overpredicts IO by up to a factor of 3. The inorganic iodine flux contributions to IO are found to be comparable to, or even greater than, the contribution of organo-iodine compounds and therefore its inclusion in atmospheric models is important to improve predictions of the influence of halogen chemistry in the marine boundary layer.

Glyoxal observations in the marine boundary layer

Anoop S. Mahajan, Cristina Prados-Roman, Timothy D. Hay, Johannes Lampel, Denis Pöhler, Katia Grossmann, Jens Tschritter, Udo Friess, Ulrich Platt, Paul Johnston, Karin Kreher, Folkard Wittrock, John P. Burrows, John M.C. Plane and Alfonso Saiz-Lopez.

J. of Geophys. Res.: atmos. DOI: 10.1002/2013JD021388

Abstract: Glyoxal is an important intermediate species formed by the oxidation of common biogenic and anthropogenic volatile organic compounds such as isoprene, toluene and acetylene. Although glyoxal has been shown to play an important role in urban and forested environments, its role in the open ocean environment is still not well understood, with only a few observations showing evidence for its presence in the open ocean marine boundary layer (MBL). In this study, we report observations of glyoxal from ten field campaigns in different parts of the world's oceans. These observations together represent the largest database of glyoxal in the MBL. The measurements are made with similar instruments that have been used in the past, although the open ocean values reported here, average of about 25 pptv with an upper limit of 40 pptv, are much lower than previously reported observations that were consistently higher than 40 pptv and had an upper limit of 140 pptv, highlighting the uncertainties in the Differential Optical Absorption Spectroscopy (DOAS) method for the retrieval of glyoxal. Despite retrieval uncertainties, the results reported in this work support previous suggestions that the currently known sources of glyoxal are insufficient to explain the average MBL concentrations. This suggests that there is an additional missing source, more than a magnitude larger than currently known sources, which is necessary to account for the observed atmospheric levels of glyoxal. Therefore it could play a more important role in the MBL than previously considered.

Observations of I2 at a remote marine site

M. J. Lawler, A. S. Mahajan, A. Saiz-Lopez, and E. S. Saltzman

Atmos. Chem. Phys., 14, 2669-2678, 2014

Abstract. Inorganic iodine plays a significant role in the photochemistry of the marine boundary layer, but the sources and cycling of iodine are not well understood. We report the first I2 observations in marine air that is not impacted by coastal macroalgal emissions or sea ice chemistry. The data clearly demonstrate that the very high I2 levels previously reported for coastal air are not representative of open ocean conditions. In this study, gas phase I2 was measured at the Cape Verde Atmospheric Observatory, a semi-remote site in the eastern tropical Atlantic, using atmospheric pressure chemical ionization tandem mass spectrometry. Atmospheric I2 levels typically increased beginning at sunset, leveled off after midnight, and then rapidly decreased at sunrise. There was also a smaller midday maximum in I2 that was probably caused by a measurement artifact. Ambient I2 mixing ratios ranged from <0.02–0.6 pmol mol−1 in May 2007 and <0.03–1.67 pmol mol−1 in May 2009. The sea-air flux implied by the nighttime buildup of I2 is too small to explain the observed daytime IO levels at this site. Iodocarbon measurements made in this region previously are also insufficient to explain the observed 1–2 pmol mol−1 of daytime IO. The observations imply the existence of an unknown daytime source of gas phase inorganic iodine. Carpenter et al. (2013) recently proposed that sea surface emissions of HOI are several times larger than the flux of I2. Such a flux could account for both the nighttime I2 and the daytime IO observations.

Enhanced production of oxidised mercury over the tropical Pacific Ocean: a key missing oxidation pathway

F. Wang, A. Saiz-Lopez, A. S. Mahajan, J. C. Gómez Martín, D. Armstrong, M. Lemes, T. Hay, and C. Prados-Roman

Atmos. Chem. Phys., 14, 1323-1335, 2014

Abstract. Mercury is a contaminant of global concern. It is transported in the atmosphere primarily as gaseous elemental mercury, but its reactivity and deposition to the surface environment, through which it enters the aquatic food chain, is greatly enhanced following oxidation. Measurements and modelling studies of oxidised mercury in the polar to sub-tropical marine boundary layer (MBL) have suggested that photolytically produced bromine atoms are the primary oxidant of mercury. We report year-round measurements of elemental and oxidised mercury, along with ozone, halogen oxides (IO and BrO) and nitrogen oxides (NO2), in the MBL over the Galápagos Islands in the equatorial Pacific. Elemental mercury concentration remained low throughout the year, while higher than expected levels of oxidised mercury occurred around midday. Our results show that the production of oxidised mercury in the tropical MBL cannot be accounted for by bromine oxidation only, or by the inclusion of ozone and hydroxyl. As a two-step oxidation mechanism, where the HgBr intermediate is further oxidised to Hg(II), depends critically on the stability of HgBr, an additional oxidant is needed to react with HgBr to explain more than 50% of the observed oxidised mercury. Based on best available thermodynamic data, we show that atomic iodine, NO2, or HO2 could all play the potential role of the missing oxidant, though their relative importance cannot be determined explicitly at this time due to the uncertainties associated with mercury oxidation kinetics. We conclude that the key pathway that significantly enhances atmospheric mercury oxidation and deposition to the tropical oceans is missing from the current understanding of atmospheric mercury oxidation.


Overview of IGAC/SPARC Chemistry-Climate Model Initiative (CCMI) Community Simulations in Support of Upcoming Ozone and Climate Assessments

V. Eyring, J.-F. Lamarque, P. Hess, F. Arfeuille, K. Bowman, M. P. Chipperfiel, B. Duncan, A. Fiore, A. Gettelman, M. A. Giorgetta, C. Granier, M. Hegglin, D. Kinnison, M. Kunze, U. Langematz, B. Luo, R. Martin, K. Matthes, P. A. Newman, T. Peter, A. Robock, T. Ryerson, A. Saiz-Lopez, et al.

SPARC Newsletter, 40, 48-66, 2013



The IGAC and SPARC communi-ties are jointly defining new refer-ence and sensitivity simulations to address emerging science ques-tions, improve process understand-ing and support upcoming ozone and climate assessments. These simulations were discussed as part of the IGAC/SPARC Global Chem-istry-Climate Modelling and Evalu-ation Workshop (Davos, May 2012) and are described in this documentThe IGAC and SPARC communi-ties are jointly defining new refer-ence and sensitivity simulations to address emerging science ques-tions, improve process understand-ing and support upcoming ozone and climate assessments. These simulations were discussed as part of the IGAC/SPARC Global Chem-istry-Climate Modelling and Evalu-ation Workshop (Davos, May 2012) and are described in this document.

Evaluating global emission inventories of biogenic bromocarbons

R. Hossaini, H. Mantle, M.P. Chipperfield, S.A. Montzka, P. Hamer, F. Ziska, B. Quack, K. Krüger, S. Tegtmeier, E. Atlas, S. Sala, A. Engel, H. Bönisch, T. Keber, D. Oram, G. Mills, C. Ordoñez, A. Saiz-Lopez, N. Warnick, Q.Liang, W. Feng, F. Moore, B.R. Miller, V. Marécal, N.A. Richards, M. Dorf, and K. Pfeilsticker.

Atmos. Chem. Phys., 13, 11819-11838, 2013

Abstract. Emissions of halogenated very short-lived substances (VSLS) are poorly constrained. However, their inclusion in global models is required to simulate a realistic inorganic bromine (Bry) loading in both the troposphere, where bromine chemistry perturbs global oxidising capacity, and in the stratosphere, where it is a major sink for ozone (O3). We have performed simulations using a 3-D chemical transport model (CTM) including three top-down and a single bottom-up derived emission inventory of the major brominated VSLS bromoform (CHBr3) and dibromomethane (CH2Br2). We perform the first concerted evaluation of these inventories, comparing both the magnitude and spatial distribution of emissions. For a quantitative evaluation of each inventory, model output is compared with independent long-term observations at National Oceanic and Atmospheric Administration (NOAA) ground-based stations and with aircraft observations made during the NSF (National Science Foundation) HIAPER Pole-to-Pole Observations (HIPPO) project. For CHBr3, the mean absolute deviation between model and surface observation ranges from 0.22 (38%) to 0.78 (115%) parts per trillion (ppt) in the tropics, depending on emission inventory. For CH2Br2, the range is 0.17 (24%) to 1.25 (167%) ppt. We also use aircraft observations made during the 2011 Stratospheric Ozone: Halogen Impacts in a Varying Atmosphere (SHIVA) campaign, in the tropical western Pacific. Here, the performance of the various inventories also varies significantly, but overall the CTM is able to reproduce observed CHBr3 well in the free troposphere using an inventory based on observed sea-to-air fluxes. Finally, we identify the range of uncertainty associated with these VSLS emission inventories on stratospheric bromine loading due to VSLS (BryVSLS). Our simulations show BryVSLS ranges from ~4.0 to 8.0 ppt depending on the inventory. We report an optimised estimate at the lower end of this range (~4 ppt) based on combining the CHBr3 and CH2Br2 inventories which give best agreement with the compilation of observations in the tropics.



A theoretical study on the formation of iodine oxides aggregates and monohydrates

Óscar Gálvez, Juan Carlos Gomez Martin, Pedro C Gomez, Alfonso Saiz-Lopez and Luis F Palacios

Phys. Chem. Chem. Phys., 2013, 15, 15572. DOI: 10.1039/c3cp51219c

Abstract. Biotic and abiotic emissions of molecular iodine and iodocarbons from the sea or ice surface and the intertidal zone to the coastal/polar marine boundary layer lead to the formation of iodine oxides, which subsequently nucleate forming iodine oxide particles (IOPs). Although the link between coastal iodine emissions and ultrafine aerosol bursts is well established, the details of the nucleation mechanism have not yet been elucidated. In this paper, results of a theoretical study of a range of potentially relevant aggregation reactions of different iodine oxides, as well as complexation with water molecules, are reported. Thermochemical properties for these reactions are obtained from high level ab initio correlated calculations including spin-orbit corrections. The results show that the nucleation path most likely proceeds through dimerisation of I2O4. It is also shown that water can hinder gas-to-particle conversion to some extent, although complexation with key iodine oxides does not remove enough of these to stop IOP formation. A consistent picture of this process emerges from the theoretical study presented here and the findings of a new laboratory study reported in the accompanying paper (Gomez Martin, et al., 2013).



Iodine chemistry in the eastern Pacific marine boundary layer

Juan C. Gómez Martín, Anoop S. Mahajan, Timothy D. Hay, Cristina Prados-Román, Carlos Ordóñez, Samantha M . McDonals, John M.C. Plane, Mar Sorribas, Manuel Gil, J. Francisco Paredes Mora, Mario V. Agama Reyes, David E. Oram, Emma Leedham, Alfonso Saiz-Lopez.

Journal of Geophysical Research: Atmospheres, vol, 118, 1-14, doi:10.1002/jgrd.50550, 2013


Abstract. Observations of gas-phase iodine species were made during a field campaign in the eastern Pacific marine boundary layer (MBL). The Climate and Halogen Reactivity Tropical Experiment (CHARLEX) in the Galápagos Islands, running from September 2010 to present, is the first long-term ground-based study of trace gases in this region. Observations of gas-phase iodine species were made using long-path differential optical absorption spectroscopy (LP-DOAS), multi-axis DOAS (MAX-DOAS), and resonance and off-resonance fluorescence by lamp excitation (ROFLEX). These measurements were supported by ancillary measurements of ozone, nitrogen oxides, and meteorological variables. Selective halocarbon and ultrafine aerosol concentration measurements were also made. MAX-DOAS observations of iodine monoxide (IO) display a weak seasonal variation. The maximum differential slant column density was 3.8 × 1013 molecule cm−2 (detection limit ~7 × 1012 molecule cm−2). The seasonal variation of reactive iodine IOx (= I + IO) is stronger, peaking at 1.6 pptv during the warm season (February–April). This suggests a dependence of the iodine sources on the annual cycle in sea surface temperature, although perturbations by changes in ocean surface iodide concentration and solar radiation are also possible. An observed negative correlation of IOx with chlorophyll-a indicates a predominance of abiotic sources. The low IO mixing ratios measured (below the LP-DOAS detection limit of 0.9 pptv) are not consistent with satellite observations if IO is confined to the MBL. The IOx loading is consistent with the observed absence of strong ozone depletion and nucleation events, indicating a small impact of iodine chemistry on these climatically relevant factors in the eastern Pacific MBL.



Modelling future changes to the stratosphere source gas injection of biogenic bromocarbons

R. Hossaini, M.P. Chipperfield, S. Dhomse, C. Ordoñez, A. Saiz-Lopez, N.H. Abraham, A. Archibald, P. Braesicke, P. Telford, N. Warwick, X. Yang and J. Pyle

Geophysical Research Letters Vol 39 issue 20, 2012, DOI: 10.1029/2012GL053401

Abstract. [1] Simulations with a chemistry-climate model (CCM) show a future increase in the stratospheric source gas injection (SGI) of biogenic very short-lived substances (VSLS). For 2000, the modelled SGI of bromine from VSLS is ∼1.7 parts per trillion (pptv) and largest over the tropical West Pacific. For 2100, this increases to ∼2.0 and ∼2.7 pptv when the model is forced with Intergovernmental Panel on Climate Change (IPCC) representative concentration pathways (RCPs) 4.5 and 8.5. The increase is largely due to stronger tropical deep convection transporting more CHBr3 to the lower stratosphere. For CH2Br2, CHBr2Cl, CH2BrCl and CHBrCl2, changes to primary oxidant OH determines their SGI contribution. Under RCP 4.5 (moderate warming), OH increases in a warmer, more humid troposphere. Under RCP 8.5 (extreme warming) OH decreases significantly due to a large methane increase, allowing greater SGI of bromine from these VSLS. Potentially enhanced VSLS emissions in the future would further increase these estimates.



Summertime NOx measurements during the CHABLIS campaign: can source and sink estimates unravel observed diurnal cycles?

S. J.-B. Bauguitte, W. J. Bloss, M. J. Evans, R. A. Salmon, P. S. Anderson, A. E. Jones, J. D. Lee, A. Saiz-Lopez, H. K. Roscoe, E. W. Wolff, and J. M. C. Plane

Atmos. Chem. Phys., 12, 989-1002, 2012

Abstract. NOx measurements were conducted at the Halley Research Station, coastal Antarctica, during the austral summer period 1 January–10 February 2005. A clear NOx diurnal cycle was observed with minimum concentrations close to instrumental detection limit (5 pptv) measured between 04:00–05:00 GMT. NOx concentrations peaked (24 pptv) between 19:00–20:00 GMT, approximately 5 h after local solar noon. An optimised box model of NOx concentrations based on production from in-snow nitrate photolysis and chemical loss derives a mean noon emission rate of 3.48 × 108 molec cm−2 s−1, assuming a 100 m boundary layer mixing height, and a relatively short NOx lifetime of ~6.4 h. This emission rate compares to directly measured values ranging from 2.1 to 12.6 × 108 molec cm−2 s−1 made on 3 days at the end of the study period. Calculations of the maximum rate of NO2 loss via a variety of conventional HOx and halogen oxidation processes show that the lifetime of NOx is predominantly controlled by halogen processing, namely BrNO3 and INO3 gas-phase formation and their subsequent heterogeneous uptake. Furthermore the presence of halogen oxides is shown to significantly perturb NOx concentrations by decreasing the NO/NO2 ratio. We conclude that in coastal Antarctica, the potential ozone production efficiency of NOx emitted from the snowpack is mitigated by the more rapid NOx loss due to halogen nitrate hydrolysis.



Reactive halogen chemistry in the troposphere

Alfonso Saiz-Lopez, Roland von Glasow

Chem. Soc. Rev., 2012, 41, 6448-6472, DOI:10.1039/C2CS35208G

Abstract. Halogen chemistry is well known for ozone destruction in the stratosphere, however reactive halogens also play an important role in the chemistry of the troposphere. In the last two decades, an increasing number of reactive halogen species have been detected in a wide range of environmental conditions from the polar to the tropical troposphere. Growing observational evidence suggests a regional to global relevance of reactive halogens for the oxidising capacity of the troposphere. This critical review summarises our current understanding and uncertainties of the main halogen photochemistry processes, including the current knowledge of the atmospheric impact of halogen chemistry as well as open questions and future research needs.



Atmospheric chemistry

Dwayne E. Heard and Alfonso Saiz-Lopez

Chem. Soc. Rev., 2012, 41, 6229-6230. DOI: 10.1039/C2CS90076A



On the sodium D line emission in the terrestrial nightglow

J.M.C. Plane, H. Oetjen, M. de Miranda, A. Saiz-Lopez, M. Gausa, B. Williams

J. Atmos. and Solar-Terrestrial Physics, 74, 181-188, 2012

Abstract. Emission from atomic Na, consisting of a doublet of lines at 589.0 and 589.6 nm, is a prominent feature of the earth’s nightglow. A large data-base of measurements of the relative intensities of the D lines (RD) was gathered at three locations: the ALOMAR observatory, Andenes (Norway, 69°N), Kuujjuarapik (Canada, 55°N) and the Danum Valley (Borneo, 8°N). RD varies between 1.5 and 2.0, with an average value of 1.67. These results were interpreted using a theoretical model of the Na nightglow which involves initial production of electronically excited NaO(A2Σ) from the reaction between Na and O3, followed either by reaction with O to generate Na(2PJ) with a branching ratio of 1/6 and a J=3/2 to 1/2 propensity of 2.0, or quenching of NaO(A) to NaO(X2Π) by O2. The resulting NaO(X) then reacts with O to generate Na(2PJ) with a branching ratio of 1/6 and a J=3/2 to 1/2 propensity of 1.5. These branching ratios and spin-orbit propensities are derived from statistical correlation of the electronic potential energy surfaces connecting the reactants NaO(A)+O and NaO(X)+O with the products Na+O2, through the Na+O2 ion-pair intermediate. A fit of this statistical model to the results of an earlier laboratory study (Slanger et al., 2005), where RD was measured as a function of the ratio [O]/[O2], indicates that the rate coefficient for the quenching of NaO(A) by O2 is around 1×10−11 cm3 molecule−1 s−1. The statistical model is also in good accord with recent high resolution observations of the Na D line widths (Harrell et al., 2010). An atmospheric model is then used to show that gravity wave-driven perturbations to the Na layer can account for the observed variability of RD.



Latitudinal distribution of reactive iodine in the Eastern Pacific and its link to open ocean sources

A. S. Mahajan, J. C. Gómez Martín, T. D. Hay, S.-J. Royer, S. Yvon-Lewis, Y. Liu, L. Hu, C. Prados-Roman, C. Ordóñez, J. M. C. Plane, and A. Saiz-Lopez.

Atmos. Chem. Phys., 12, 11609-11617, 2012

Abstract. Ship-based Multi-Axis Differential Optical Absorption Spectroscopy measurements of iodine monoxide (IO) and atmospheric and seawater Gas Chromatography-Mass Spectrometer observations of methyl iodide (CH3I) were made in the Eastern Pacific marine boundary layer during April 2010 as a part of the HaloCarbon Air Sea Transect-Pacific (HaloCAST-P) scientific cruise. The presence of IO in the open ocean environment was confirmed, with a maximum differential slant column density of 5 × 1013 molecules cm−2 along the 1° elevation angle (corresponding to approximately 1 pptv) measured in the oligotrophic region of the Southeastern Pacific. Such low IO mixing ratios and their observed geographical distribution are inconsistent with satellite estimates and with previous understanding of oceanic sources of iodine. A strong correlation was observed between reactive iodine (defined as IO + I) and CH3I, suggesting common sources. In situ measurements of meteorological parameters and physical ocean variables, along with satellite-based observations of Chlorophyll a (Chl a) and Chromophoric Dissolved Organic Matter (CDOM) were used to gain insight into the possible sources of iodine in this remote environment. Surprisingly, reactive iodine showed a negative correlation (> 99% confidence) to Chl a and CDOM across the cruise transect. However, a significant positive correlation (> 99% confidence) with sea surface temperature (SST) and salinity instead suggests a widespread abiotic source related to the availability of aqueous iodine and to temperature. 



Iodine monoxide in the north subtropical free troposphere

O. Puentedura, M. Gil, A. Saiz-Lopez, T. Hay, M. Navarro-Comas, A. Gómez-Pelaez, E. Cuevas, J. Iglesias, and L. Gomez

Atmos. Chem. Phys., 12, 4909-4921, 2012

Abstract. Iodine monoxide (IO) differential slant column densities (DSCD) have been retrieved from a new multi-axis differential optical absorption spectroscopy (MAX-DOAS) instrument deployed at the Izaña subtropical observatory as part of the Network for the Detection of Atmospheric Composition Change (NDACC) programme. The station is located at 2370 m a.s.l., well above the trade wind inversion that limits the top of the marine boundary layer, and hence is representative of the free troposphere. We report daily observations from May to August 2010 at different viewing angles. During this period, the spectral signature of IO was unequivocally detected on every day of measurement. A mean IO DSCD of 1.52×1013 molecules cm−2 was observed at the 5° instrument elevation angle (IEA) on clear days using a single zenith reference for the reported period, with a day-to-day variability of 33% at one standard deviation. Based on the simulation of the DSCDs using radiative transfer calculations with five different hypothesized IO profiles, the IO mixing ratio is estimated to range between 0.2 and 0.4 pptv in the free troposphere. Episodes of Saharan dust outbreaks were also observed, with large increases in the DSCDs at higher IEA, suggesting an enhancement of IO inside the dust cloud.


Iodine emissions from the sea ice of the Weddell Sea

H. M. Atkinson, R.-J. Huang, R. Chance, H. K. Roscoe, C. Hughes, B. Davison, A. Schönhardt, A. S. Mahajan, A. Saiz-Lopez, T. Hoffmann, and P. S. Liss

Atmos. Chem. Phys., 12, 11229-11244, 2012

Abstract. Iodine compounds were measured above, below and within the sea ice of the Weddell Sea during a cruise in 2009, to make progress in elucidating the mechanism of local enhancement and volatilisation of iodine. I2 mixing ratios of up to 12.4 pptv were measured 10 m above the sea ice, and up to 31 pptv was observed above surface snow on the nearby Brunt Ice Shelf – large amounts. Atmospheric IO of up to 7 pptv was measured from the ship, and the average sum of HOI and ICl was 1.9 pptv. These measurements confirm the Weddell Sea as an iodine hotspot. Average atmospheric concentrations of CH3I, C2H5I, CH2ICl, 2-C3H7I, CH2IBr and 1-C3H7I were each 0.2 pptv or less. On the Brunt Ice Shelf, enhanced concentrations of CH3I and C2H5I (up to 0.5 and 1 pptv respectively) were observed in firn air, with a diurnal profile that suggests the snow may be a source. In the sea ice brine, iodocarbons concentrations were over 10 times those of the sea water below. The sum of iodide + iodate was depleted in sea ice samples, suggesting some missing iodine chemistry. Flux calculations suggest I2 dominates the iodine atom flux to the atmosphere, but models cannot reconcile the observations and suggest either a missing iodine source or other deficiencies in our understanding of iodine chemistry. The observation of new particle formation, consistent with the model predictions, strongly suggests an iodine source. This combined study of iodine compounds is the first of its kind in this unique region of sea ice rich in biology and rich in iodine chemistry.



Halogen activation via interactions with environmental ice and snow in the polar lower troposphere and other regions

J. P. D. Abbatt, J. L. Thomas, K. Abrahamsson, C. Boxe, A. Granfors, A. E. Jones, M. D. King, A. Saiz-Lopez, P. B. Shepson, J. Sodeau, D. W. Toohey, C. Toubin, R. von Glasow, S. N. Wren, and X. Yang

Atmos. Chem. Phys., 12, 6237-6271, 2012

Abstract. The role of ice in the formation of chemically active halogens in the environment requires a full understanding because of its role in atmospheric chemistry, including controlling the regional atmospheric oxidizing capacity in specific situations. In particular, ice and snow are important for facilitating multiphase oxidative chemistry and as media upon which marine algae live. This paper reviews the nature of environmental ice substrates that participate in halogen chemistry, describes the reactions that occur on such substrates, presents the field evidence for ice-mediated halogen activation, summarizes our best understanding of ice-halogen activation mechanisms, and describes the current state of modeling these processes at different scales. Given the rapid pace of developments in the field, this paper largely addresses advances made in the past five years, with emphasis given to the polar boundary layer. The integrative nature of this field is highlighted in the presentation of work from the molecular to the regional scale, with a focus on understanding fundamental processes. This is essential for developing realistic parameterizations and descriptions of these processes for inclusion in larger scale models that are used to determine their regional and global impacts.



Estimating the climate significance of halogen-driven ozone loss in the tropical marine troposphere

A. Saiz-Lopez, J.-F. Lamarque, D. E. Kinnison, S. Tilmes, C. Ordóñez, J. J. Orlando, A. J. Conley, J. M. C. Plane, A. S. Mahajan, G. Sousa Santos, E. L. Atlas, D. R. Blake, S. P. Sander, S. Schauffler, A. M. Thompson, and G. Brasseur

Atmos. Chem. Phys., 12, 3939-3949, 2012


Abstract. We have integrated observations of tropospheric ozone, very short-lived (VSL) halocarbons and reactive iodine and bromine species from a wide variety of tropical data sources with the global CAM-Chem chemistry-climate model and offline radiative transfer calculations to compute the contribution of halogen chemistry to ozone loss and associated radiative impact in the tropical marine troposphere. The inclusion of tropospheric halogen chemistry in CAM-Chem leads to an annually averaged depletion of around 10% (~2.5 Dobson units) of the tropical tropospheric ozone column, with largest effects in the middle to upper troposphere. This depletion contributes approximately −0.10 W m−2 to the radiative flux at the tropical tropopause. This negative flux is of similar magnitude to the ~0.33 W m−2 contribution of tropospheric ozone to present-day radiative balance as recently estimated from satellite observations. We find that the implementation of oceanic halogen sources and chemistry in climate models is an important component of the natural background ozone budget and we suggest that it needs to be considered when estimating both preindustrial ozone baseline levels and long term changes in tropospheric ozone.



Bromine and iodine chemistry in a global chemistry-climate model: description and evaluation of very short-lived oceanic sources

C. Ordóñez, J.-F. Lamarque, S. Tilmes, D. E. Kinnison, E. L. Atlas, D. R. Blake, G. Sousa Santos, G. Brasseur, and A. Saiz-Lopez

Atmos. Chem. Phys., 12, 1423-1447, 2012

Abstract. The global chemistry-climate model CAM-Chem has been extended to incorporate an expanded bromine and iodine chemistry scheme that includes natural oceanic sources of very short-lived (VSL) halocarbons, gas-phase photochemistry and heterogeneous reactions on aerosols. Ocean emissions of five VSL bromocarbons (CHBr3, CH2Br2, CH2BrCl, CHBrCl2, CHBr2Cl) and three VSL iodocarbons (CH2ICl, CH2IBr, CH2I2) have been parameterised by a biogenic chlorophyll-a (chl-a) dependent source in the tropical oceans (20° N–20° S). Constant oceanic fluxes with 2.5 coast-to-ocean emission ratios are separately imposed on four different latitudinal bands in the extratropics (20°–50° and above 50° in both hemispheres). Top-down emission estimates of bromocarbons have been derived using available measurements in the troposphere and lower stratosphere, while iodocarbons have been constrained with observations in the marine boundary layer (MBL). Emissions of CH3I are based on a previous inventory and the longer lived CH3Br is set to a surface mixing ratio boundary condition. The global oceanic emissions estimated for the most abundant VSL bromocarbons – 533 Gg yr−1 for CHBr3 and 67.3 Gg yr−1 for CH2Br2 – are within the range of previous estimates. Overall the latitudinal and vertical distributions of modelled bromocarbons are in good agreement with observations. Nevertheless, we identify some issues such as the reduced number of aircraft observations to validate models in the Southern Hemisphere, the overestimation of CH2Br2 in the upper troposphere – lower stratosphere and the underestimation of CH3I in the same region. Despite the difficulties involved in the global modelling of the shortest lived iodocarbons (CH2ICl, CH2IBr, CH2I2), modelled results are in good agreement with published observations in the MBL. Finally, sensitivity simulations show that knowledge of the diurnal emission cycle for these species, in particular for CH2I2, is key to assess their global source strength.



Atmospheric Chemistry of Iodine

Alfonso Saiz-Lopez, John M. C. Plane, Alex R. Baker, Lucy J. Carpenter, Roland von Glasow, Juan C. Gómez Martín, Gordon McFiggans, and Russell W. Saunders

Chem. Rev., 2012, 112 (3), pp 1773–1804, doi: 10.1021/cr200029u



An active nitrogen cycle on Mars sufficient to support a subsurface biosphere

C.S. Boxe, K.P. Hand, K.H. Nealson, Y.L. Yung and A. Saiz-Lopez

International Journal of Astrobiology, 1(2): 109-115 (2012)

Abstract. Mars' total atmospheric nitrogen content is 0.2 mbar. One-dimensional (1D) photochemical simulations of Mars' atmosphere show that nitric acid (HNO3(g)), the most soluble nitrogen oxide, is the principal reservoir species for nitrogen in its lower atmosphere, which amounts to a steady-state value of 6×10−2 kg or 4 moles, conditions of severe nitrogen deficiency. Mars could, however, support ∼1015 kg of biomass (∼1 kg N m−2) from its current atmospheric nitrogen inventory. The terrestrial mass ratio of nitrogen in biomass to that in the atmosphere is ∼10−5; applying this ratio to Mars yields ∼1010 kg of total biomass – also, conditions of severe nitrogen deficiency. These amounts, however, are lower limits as the maximum surface-sink of atmospheric nitrogen is 2.8 mbar (9×1015 kg of N), which indicates, in contradistinction to the Klingler et al. (1989), that biological metabolism would not be inhibited in the subsurface of Mars. Within this context, we explore HNO3 deposition on Mars' surface (i.e. soil and ice-covered regions) on pure water metastable thin liquid films. We show for the first time that the negative change in Gibbs free energy increases with decreasing HNO3(g) (NO3(aq)) in metastable thin liquid films that may exist on Mars' surface. We also show that additional reaction pathways are exergonic and may proceed spontaneously, thus providing an ample source of energy for nitrogen fixation on Mars. Lastly, we explore the dissociation of HNO3(g) to form NO3(aq) in metastable thin liquid films on the Martian surface via condensed phase simulations. These simulations show that photochemically produced fixed nitrogen species are not only released from the Martian surface to the gas-phase, but more importantly, transported to lower depths from the Martian surface in transient thin liquid films. A putative biotic layer at 10 m depth would produce HNO3 and N2 sinks of −54 and −5×1012 molecules cm−2 s−1, respectively, which is an ample supply of available nitrogen that can be efficiently transported to the subsurface. The downward transport as well as the release to the atmosphere of photochemically produced fixed nitrogen species (e.g. NO2, NO and NO2) suggests the existence of a transient but active nitrogen cycle on Mars.



Adsorbed water and thin liquid films on Mars,

C.S. Boxe, K. P. Hand, K. H. Nealson, Y. L. Yung, A. S. Yen, and A. Saiz-Lopez

International Journal of Astrobiology, doi:10.1017/S147355041200080, 2012

Abstract. At present, bulk liquid water on the surface and near-subsurface of Mars does not exist due to the scarcity of condensed- and gas-phase water, pressure and temperature constraints. Given that the nuclei of soil and ice, that is, the soil solid and ice lattice, respectively, are coated with adsorbed and/or thin liquid films of water well below 273 K and the availability of water limits biological activity, we quantify lower and upper limits for the thickness of such adsorbed/water films on the surface of the Martian regolith and for subsurface ice. These limits were calculated based on experimental and theoretical data for pure water ice and water ice containing impurities, where water ice containing impurities exhibit thin liquid film enhancements, ranging from 3 to 90. Close to the cold limit of water stability (i.e. 273 K), thin liquid film thicknesses at the surface of the Martian regolith is 0.06 nm (pure water ice) and ranges from 0.2 to 5 nm (water ice with impurities). An adsorbed water layer of 0.06 nm implies a dessicated surface as the thickness of one monolayer of water is 0.3 nm but represents 0.001–0.02% of the Martian atmospheric water vapour inventory. Taking into account the specific surface area (SSA) of surface-soil (i.e. top 1 mm of regolith and 0.06 nm adsorbed water layer), shows Martian surface-soil may contain interfacial water that represents 6–66% of the upper- and lower-limit atmospheric water vapour inventory and almost four times and 33%, the lower- and upper-limit Martian atmospheric water vapour inventory. Similarly, taking the SSA of Martian soil, the top 1 mm or regolith at 5 nm thin liquid water thickness, yields 1.10×1013 and 6.50×1013 litres of waters, respectively, 55–325 times larger than Mars’ atmospheric water vapour inventory. Film thicknesses of 0.2 and 5 nm represent 2.3×104–1.5×106 litres of water, which is 6.0×10−7–4.0×10−4%, respectively, of a 10 pr μm water vapour column, and 3.0×10−6–4.0×10−4% and 6.0×10−6–8.0×10−4%, respectively, of the Martian atmospheric water vapour inventory. Thin liquid film thicknesses on/in subsurface ice were investigated via two scenarios: (i) under the idealistic case where it is assumed that the diurnal thermal wave is equal to the temperature of ice tens of centimetres below the surface, allowing for such ice to experience temperatures close to 273 K and (ii) under the, likely, realistic scenario where the diurnal thermal wave allows for the maximum subsurface ice temperature of 235 K at 1 m depth between 30°N and 30°S. Scenario 1 yields thin liquid film thicknesses ranging from 11 to 90 nm; these amounts represent 4×106–3.0×107 litres of water. For pure water ice, Scenario 2 reveals that the thickness of thin liquid films contained on/within Martian subsurface is less than 1.2 nm, several molecular layers thick. Conversely, via the effect of impurities at 235 K allows for a thin liquid film thickness on/within subsurface ice of 0.5 nm, corresponding to 6.0×104 litres of water. The existence of thin films on Mars is supported by data from the Mars Exploration Rovers (MERs) Spirit and Opportunity's Alpha Proton X-ray Spectrometer instrumentation, which have detected increased levels of bromine beneath the immediate surface, suggestive of the mobilization of soluble salts by thin films of liquid water towards local cold traps. These findings show that biological activity on the Martian surface and subsurface is not limited by nanometre dimensions of available water.



The multi-seasonal NOy budget in coastal Antarctica and its link with surface snow and ice core nitrate: results from the CHABLIS campaign

A. E. Jones, E. W. Wolff, D. Ames, S. J.-B. Bauguitte, K. C. Clemitshaw, Z. Fleming, G. P. Mills, A. Saiz-Lopez, R. A. Salmon, W. T. Sturges, and D. R. Worton

Atmos. Chem. Phys., 11, 9271-9285, 2011

Abstract. Measurements of a suite of individual NOy components were carried out at Halley station in coastal Antarctica as part of the CHABLIS campaign (Chemistry of the Antarctic Boundary Layer and the Interface with Snow). Conincident measurements cover over half a year, from austral winter 2004 through to austral summer 2005. Results show clear dominance of organic NOy compounds (PAN and MeONO2) during the winter months, with low concentrations of inorganic NOy. During summer, concentrations of inorganic NOy compounds are considerably greater, while those of organic compounds, although lower than in winter, are nonetheless significant. The relative concentrations of the alkyl nitrates, as well as their seasonality, are consistent with an oceanic source. Multi-seasonal measurements of surface snow nitrate correlate strongly with inorganic NOy species (especially HNO3) rather than organic. One case study in August suggested that, on that occasion, particulate nitrate was the dominant source of nitrate to the snowpack, but this was not the consistent picture throughout the measurement period. An analysis of NOx production rates showed that emissions of NOx from the snowpack overwhelmingly dominate over gas-phase sources. This result suggests that, for certain periods in the past, the flux of NOx into the Antarctic boundary layer can be calculated from ice core nitrate data.



In situ detection of atomic and molecular iodine using Resonance and Off-Resonance Fluorescence by Lamp Excitation: ROFLEX

Gómez Martín, J. C., Blahins, J., Gross, U., Ingham, T., Goddard, A., Mahajan, A. S., Ubelis, A., and Saiz-Lopez, A.

Atmos. Meas. Tech., 4, 29-45, doi:10.5194/amt-4-29-2011, 2011

Abstract. We demonstrate a new instrument for in situ detection of atmospheric iodine atoms and molecules based on atomic and molecular resonance and off-resonance ultraviolet fluorescence excited by lamp emission. The instrument combines the robustness, light weight, low power consumption and efficient excitation of radio-frequency discharge light sources with the high sensitivity of the photon counting technique. Calibration of I2 fluorescence is achieved via quantitative detection of the molecule by Incoherent Broad Band Cavity-enhanced Absorption Spectroscopy. Atomic iodine fluorescence signal is calibrated by controlled broad band photolysis of known I2 concentrations in the visible spectral range at atmospheric pressure. The instrument has been optimised in laboratory experiments to reach detection limits of 1.2 pptv for I atoms and 13 pptv for I2, for S/N = 1 and 10 min of integration time. The ROFLEX system has been deployed in a field campaign in northern Spain, representing the first concurrent observation of ambient mixing ratios of iodine atoms and molecules in the 1–350 pptv range.



DOAS observations of formaldehyde and its impact on the HOx balance in the tropical Atlantic marine boundary layer

Mahajan, A. S., Whalley, L. K., Kozlova, E., Oetjen, H., Mendez, L., Furneaux, K. L., Goddard, A., Heard, D. E., Plane, J. M. C. and Saiz-Lopez, A.

J. Atmos. Chem., doi:10.1007/s10874-011-9200-7, 2011

Abstract. Measurements of formaldehyde (HCHO) were made at the Cape Verde Atmospheric Observatory between November 2006 and June 2007 using the Long-Path Differential Optical Absorption Spectroscopy (LP-DOAS) technique. Observations show that typical HCHO mixing ratios ranged between 350 and 550 pptv (with typical 2-σ uncertainties of ~110 pptv), with several events of high HCHO, the maximum being 1,885 ± 149 pptv. The observations indicate a lack of strong seasonal or diurnal variations, within the uncertainty of the measurements. A box model is employed to test whether the observations can be explained using known hydrocarbon photochemistry; the model replicates well the typical diurnal profile and monthly mean values. The model results indicate that on average 20% of HO2 production and 10% of OH destruction can be attributed to the mean HCHO levels, suggesting that even at these low average mixing ratios HCHO plays an important role in determining the HOx (HO2+OH) balance of the remote marine boundary layer.



Concurrent observations of atomic iodine, molecular iodine and ultrafine particles in a coastal environment

A. S. Mahajan, M. Sorribas, J. C. Gómez Martín, S. M. MacDonald, M. Gil, J. M. C. Plane, and A. Saiz-Lopez

Atmos. Chem. Phys., 11, 2545-2555, 2011

Abstract. Simultaneous measurements of atomic iodine (I), molecular iodine (I2) and ultrafine particles were made at O Grove, Galicia (42.50° N, 8.87° W), on the northwest coast of Spain. The observations show a strong tidal signature, and indicate that the most probable sources of reactive iodine species are the exposed macroalgae during low tide. For the first time, I2 and I were concurrently measured revealing a high average I2/I ratio of ~32, which is higher than previously inferred by modelling studies. A 1-dimensional photochemical model is employed to simulate the observations showing that the high I2/I ratio can be reproduced in the presence of fast vertical mixing close to the surface, or using an extra chemical loss for I atoms with an unknown species. There is a lack of strong correlation between the I2/I and ultrafine particles, indicating that although they both have macroalgal sources, these were not at the same location. The model simulations also suggest that the source of the observed ultrafine particles is likely not very close to the measurement site, in order for the particles to form and grow, but the source for I and I2 must be local. Finally, the effect of NOx levels on iodine oxides, and the conditions under which iodine particle bursts will be suppressed, are explored.



Reactive Halogens in the Marine Boundary Layer (RHaMBLe): the tropical North Atlantic experiments

J. D. Lee, G. McFiggans, J. D. Allan, A. R. Baker, S. M. Ball, A. K. Benton, L. J. Carpenter, R. Commane, B. D. Finley, M. Evans, E. Fuentes, K. Furneaux, A. Goddard, N. Good, J. F. Hamilton, D. E. Heard, H. Herrmann, A. Hollingsworth, J. R. Hopkins, T. Ingham, M. Irwin, C. E. Jones, R. L. Jones, W. C. Keene, M. J. Lawler, S. Lehmann, A. C. Lewis, M. S. Long, A. Mahajan, J. Methven, S. J. Moller, K. Müller, T. Müller, N. Niedermeier, S. O'Doherty, H. Oetjen, J. M. C. Plane, A. A. P. Pszenny, K. A. Read, A. Saiz-Lopez, E. S. Saltzman, R. Sander, R. von Glasow, L. Whalley, A. Wiedensohler, and D. Young

Atmos. Chem. Phys., 10, 1031-1055, 2010


Abstract. The NERC UK SOLAS-funded Reactive Halogens in the Marine Boundary Layer (RHaMBLe) programme comprised three field experiments. This manuscript presents an overview of the measurements made within the two simultaneous remote experiments conducted in the tropical North Atlantic in May and June 2007. Measurements were made from two mobile and one ground-based platforms. The heavily instrumented cruise D319 on the RRS Discovery from Lisbon, Portugal to São Vicente, Cape Verde and back to Falmouth, UK was used to characterise the spatial distribution of boundary layer components likely to play a role in reactive halogen chemistry. Measurements onboard the ARSF Dornier aircraft were used to allow the observations to be interpreted in the context of their vertical distribution and to confirm the interpretation of atmospheric structure in the vicinity of the Cape Verde islands. Long-term ground-based measurements at the Cape Verde Atmospheric Observatory (CVAO) on São Vicente were supplemented by long-term measurements of reactive halogen species and characterisation of additional trace gas and aerosol species during the intensive experimental period.

This paper presents a summary of the measurements made within the RHaMBLe remote experiments and discusses them in their meteorological and chemical context as determined from these three platforms and from additional meteorological analyses. Air always arrived at the CVAO from the North East with a range of air mass origins (European, Atlantic and North American continental). Trace gases were present at stable and fairly low concentrations with the exception of a slight increase in some anthropogenic components in air of North American origin, though NOx mixing ratios during this period remained below 20 pptv (note the non-IUPAC adoption in this manuscript of pptv and ppbv, equivalent to pmol mol−1 and nmol mol−1 to reflect common practice). Consistency with these air mass classifications is observed in the time series of soluble gas and aerosol composition measurements, with additional identification of periods of slightly elevated dust concentrations consistent with the trajectories passing over the African continent. The CVAO is shown to be broadly representative of the wider North Atlantic marine boundary layer; measurements of NO, O3 and black carbon from the ship are consistent with a clean Northern Hemisphere marine background. Aerosol composition measurements do not indicate elevated organic material associated with clean marine air. Closer to the African coast, black carbon and NO levels start to increase, indicating greater anthropogenic influence. Lower ozone in this region is possibly associated with the increased levels of measured halocarbons, associated with the nutrient rich waters of the Mauritanian upwelling. Bromide and chloride deficits in coarse mode aerosol at both the CVAO and on D319 and the continuous abundance of inorganic gaseous halogen species at CVAO indicate significant reactive cycling of halogens.

Aircraft measurements of O3 and CO show that surface measurements are representative of the entire boundary layer in the vicinity both in diurnal variability and absolute levels. Above the inversion layer similar diurnal behaviour in O3 and CO is observed at lower mixing ratios in the air that had originated from south of Cape Verde, possibly from within the ITCZ. ECMWF calculations on two days indicate very different boundary layer depths and aircraft flights over the ship replicate this, giving confidence in the calculated boundary layer depth.



Measurement and modelling of tropospheric reactive halogen species over the tropical Atlantic Ocean

A. S. Mahajan, J. M. C. Plane, H. Oetjen, L. Mendes, R. W. Saunders, A. Saiz-Lopez, C. E. Jones, L. J. Carpenter, and G. B. McFiggans

Atmos. Chem. Phys., 10, 4611-4624, 2010

Abstract. Although tropospheric reactive halogen chemistry is well studied in coastal and polar environments, the presence of halogens over the open ocean environment has not been widely reported. The impacts of halogens on the tropical open ocean marine boundary layer (MBL), in particular, are not well characterised. This paper describes observations of iodine monoxide (IO) and bromine oxide (BrO) over eight months in the tropical open ocean MBL, on the north-eastern side of São Vicente (Cape Verde Islands, 16.85° N, 24.87° W). The highest BrO mixing ratio observed was 5.6±1 pmol mol−1, while the maximum observed IO mixing ratio was 3.1±0.4 pmol mol−1. The average values seen between 09:00–17:00 GMT were ~2.8 pmol mol−1 for BrO and ~1.5 pmol mol−1 for IO; these averages showed little variability over the entire campaign from November 2006 to June 2007. A 1-dimensional chemistry and transport model is used to study the evolution of iodine species and quantify the combined impact of iodine and bromine chemistry on the oxidising capacity of the MBL. It appears that the measured fluxes of iodocarbons are insufficient to account for the observed levels of IO, and that an additional I atom source is required, possibly caused by the deposition of O3 onto the ocean surface in the presence of solar radiation. Modelling results also show that the O3 depletion observed at Cape Verde cannot be explained in the absence of halogen chemistry, which contributes ~45% of the observed O3 depletion at the height of measurements (10 m) during summer. The model also predicts that halogens decrease the hydroperoxy radical (HO2) concentration by ~14% and increase the hydroxyl radical (OH) concentration by ~13% near the ocean surface. The oxidation of dimethyl sulphide (DMS) by BrO takes place at a comparable rate to oxidation by OH in this environment. Finally, the potential of iodine chemistry to form new particles is explored and conditions under which particle formation could be important in the remote MBL are discussed.



Coupling of HOx, NOx and halogen chemistry in the antarctic boundary layer

W. J. Bloss, M. Camredon, J. D. Lee, D. E. Heard, J. M. C. Plane, A. Saiz-Lopez, S. J.-B. Bauguitte, R. A. Salmon, and A. E. Jones

Atmos. Chem. Phys., 10, 10187-10209, 2010

Abstract. A modelling study of radical chemistry in the coastal Antarctic boundary layer, based upon observations performed in the course of the CHABLIS (Chemistry of the Antarctic Boundary Layer and the Interface with Snow) campaign at Halley Research Station in coastal Antarctica during the austral summer 2004/2005, is described: a detailed zero-dimensional photochemical box model was used, employing inorganic and organic reaction schemes drawn from the Master Chemical Mechanism, with additional halogen (iodine and bromine) reactions added. The model was constrained to observations of long-lived chemical species, measured photolysis frequencies and meteorological parameters, and the simulated levels of HOx, NOx and XO compared with those observed. The model was able to replicate the mean levels and diurnal variation in the halogen oxides IO and BrO, and to reproduce NOx levels and speciation very well. The NOx source term implemented compared well with that directly measured in the course of the CHABLIS experiments. The model systematically overestimated OH and HO2 levels, likely a consequence of the combined effects of (a) estimated physical parameters and (b) uncertainties within the halogen, particularly iodine, chemical scheme. The principal sources of HOx radicals were the photolysis and bromine-initiated oxidation of HCHO, together with O(1D) + H2O. The main sinks for HOx were peroxy radical self- and cross-reactions, with the sum of all halogen-mediated HOx loss processes accounting for 40% of the total sink. Reactions with the halogen monoxides dominated CH3O2-HO2-OH interconversion, with associated local chemical ozone destruction in place of the ozone production which is associated with radical cycling driven by the analogous NO reactions. The analysis highlights the need for observations of physical parameters such as aerosol surface area and boundary layer structure to constrain such calculations, and the dependence of simulated radical levels and ozone loss rates upon a number of uncertain kinetic and photochemical parameters for iodine species.



Reactive iodine species in semi-polluted environments

Mahajan, A. S., Oetjen, H., Saiz-Lopez, A., Lee, J. D., McFiggans, B. G., and Plane, J. M. C.

Geosphys. Res. Letters., 36, L16803, doi:10.1029-2009GL038018, 2009

Abstract. Iodine chemistry in the marine boundary layer has attracted increasing attention over the last few years because iodine oxides cause ozone destruction, change the atmospheric oxidising capacity, and can form ultrafine particles. However, the chemistry of iodine in polluted environments is not well understood: its effects are assumed to be inhibited by reactions involving NOx (NO2 & NO). This paper describes Differential Optical Absorption Spectroscopy (DOAS) observations of iodine species (I2, OIO and IO) and the nitrate radical (NO3) at a semi-polluted coastal site in Roscoff, France. Significant concentrations of IO and I2 were measured during daytime, indicating efficient recycling of iodine from iodine nitrate (IONO2). I2, IO, OIO and NO3 were observed at night. These observations are interpreted using a one dimensional model to demonstrate that iodine plays an important role even in polluted environments due to recycling mechanisms not considered previously.



Iodine in the air: Origin, Transformation and Exchange to Mammals

Saunders, R. W., and A. Saiz-Lopez

In: Comprehensive Handbook of Iodine. V. R. Preedy, G. Burrow, and R. Watson (eds), Oxford: Academic Press, 2009, pp. 76-82


Influence of thin liquid films on polar ice chemistry: Implications for Earth and planetary science

Boxe, C. S., and Saiz-Lopez, A.

Polar Science, 3, 73-81, 2009

Abstract. The polar snowpack (and sea-ice) plays a major role in affecting overlying boundary layer chemistry and has only recently come to light. Furthermore, the understanding of this system and its importance is steadily growing. Investigations done thus far, nonetheless, examined the subsets of the polar environment as an uncoupled system. Analogous to some materials, the surface of snow/ice exhibits thin liquid layers (e.g., the quasi-liquid layer (QLL) and brine layer (BL)). This paper gives an overview of thin liquid films and illustrations of their function in Earth science. The impact of such films in polar science (i.e., polar snowpack photochemistry) is discussed within the context of how field data has been elucidated through laboratory data and modeling techniques. Specifically, what laboratory and modeling investigations have revealed about the effect of thin liquid layers on constraining field observations and, more importantly, the physicochemical mechanisms that govern the behavior of trace gases within the snowpack (and sea-ice) and how they are released from the polar snowpack. Current and future impacts of these findings are discussed, along with putative implications of the effect of thin liquid films in planetary science.



High bromine oxide concentrations in the semi-polluted boundary layer

Mahajan, A. S., Oetjen, H., Lee, J. D., Saiz-Lopez, A., McFiggans, B. G., and Plane, J. M. C.

Atmos. Environ., 43, 3811-3818, 2009

Abstract. Bromine chemistry in the marine boundary layer is recognized to play an important role through catalytic ozone destruction, changes to the atmospheric oxidising capacity (by changing the OH/HO2 and NO/NO2 ratio) and oxidation of compounds such as dimethyl sulphide (DMS). However, the chemistry of bromine in polluted environments is not well understood and its effects are thought to be inhibited by reactions involving NOx (NO2 & NO). This paper describes long-path Differential Optical Absorption Spectroscopy (DOAS) observations of bromine oxide (BrO) at a semi-polluted coastal site in Roscoff, France. Significant concentrations of BrO (up to 7.5 ± 1.0 pptv) were measured during daytime, indicating the presence of unknown sources or efficient recycling of reactive bromine from bromine nitrate (BrONO2), which should be the major reservoir for bromine in a high NOx environment. These measurements indicate that bromine chemistry can play an important role in polluted environments.



A mechanism for biologically-inducediodine emissions from sea-ice

A. Saiz-Lopez and C. S. Boxe

Atmos. Chem. Phys. Discuss., 8, 2953–2976, 2008



Only recently, ground- and satellite-based measurements have reported high concentrations of IO in coastal Antarctica. The sources of such a large iodine burden in the Antarctic atmosphere remain unknown. We propose a novel mechanism for iodine release from sea-ice surfaces. The release is triggered by the biological production of iodide (I-) and hypoiodous acid (HOI) from marine algae, contained within and underneath sea-ice, and their diffusion through sea-ice brine channels to accumulate in the quasi-liquid layer on the surface of sea-ice. A multiphase chemical model of polar atmospheric chemistry has been developed to investigate the biology-ice-atmosphere coupling in the polar environment. Model simulations were conducted to interpret recent observations of elevated IO in the coastal Antarctic springtime. The results show that the levels of inorganic iodine (i.e. I2, IBr, ICl) released from sea-ice through this mechanism account for the observed IO concentrations in the Antarctic springtime environment. The model results also indicate that iodine may trigger the catalytic release of bromine from sea-ice through phase equilibration of IBr. Considering the extent of sea-ice around the Antarctic continent, we suggest that the resulting high levels of iodine may have widespread impact on catalytic ozone destruction and aerosol formation in the Antarctic lower troposphere.

Year- round observations of NO, NO2, O3, SO2 and toluene measured with a DOAS system in Central Spain (Puertollano)

Saiz-Lopez, A., Notario, A., Albaladejo, J., Poblete, J., Adame, J. A., and Bolivar, J. P.

Water Air and Soil Pollution, DOI 10.1007/s11270-008-9912-8, 2008

Abstract. We report observations of primary and secondary atmospheric pollutants such as nitrogen oxides, sulfur dioxide, toluene, and ozone during the period February 2002 to August 2003 in Puertollano, an industrial area located in central–southern Spain. The measurements were performed using a commercial differential optical absorption spectroscopy instrument. From the hourly data, we have analyzed the mean seasonal levels and the daily evolution and we have examined the occurrence of elevated pollution episodes. The daily cycles of NO, NO2, SO2, and toluene were characterized by an early-morning maximum whereas O3 peaks were monitored around noon. Seasonally, the highest hourly mean concentrations of NO, NO2, SO2, and toluene, 14.2, 27.0, 34.4, and 12.1 μg m−3 respectively, were found in the winter while O3 summer levels reached 119.1 μg m−3. The dataset presented here shows episodic occurrences of elevated concentrations that exceeded the maximum levels established in the European Directives. For instance, hourly values for SO2 were repeatedly measured above 350 μg m−3. During the period of measurements, the O3 thresholds (i.e., hourly value of 240 μg m−3) defined to protect the human health have also been exceeded numerous times. Finally, we investigate daily and seasonal patterns in pollution levels within the context of local meteorology and photochemistry, vehicular traffic, and industrial emissions.



Multiphase modelling of nitrate photochemistry in the quasi- liquid layer (QLL): implications for NOx release from the Arctic and coastal Antarctic snowpack

Boxe, C. S. and A. Saiz-Lopez

Atmospheric Chemistry and Physics. 8, 4855-4864, 2008

Abstract. We utilize a multiphase model, CON-AIR (Condensed Phase to Air Transfer Model), to show that the photochemistry of nitrate (NO3) in and on ice and snow surfaces, specifically the quasi-liquid layer (QLL), can account for NOx volume fluxes, concentrations, and [NO]/[NO2] (γ=[NO]/[NO2]) measured just above the Arctic and coastal Antarctic snowpack. Maximum gas phase NOx volume fluxes, concentrations and γ simulated for spring and summer range from 5.0×104 to 6.4×105 molecules cm−3 s−1, 5.7×108 to 4.8×109 molecules cm−3, and ~0.8 to 2.2, respectively, which are comparable to gas phase NOx volume fluxes, concentrations and γ measured in the field. The model incorporates the appropriate actinic solar spectrum, thereby properly weighting the different rates of photolysis of NO3 and NO2. This is important since the immediate precursor for NO, for example, NO2, absorbs at wavelengths longer than nitrate itself. Finally, one-dimensional model simulations indicate that both gas phase boundary layer NO and NO2 exhibit a negative concentration gradient as a function of height although [NO]/[NO2] are approximately constant. This gradient is primarily attributed to gas phase reactions of NOx with halogens oxides (i.e. as BrO and IO), HOx, and hydrocarbons, such as CH3O2.



On the vertical distribution of boundary layer halogens over coastal Antarctica: implications for O3, HOx, NOx and the Hg lifetime

Saiz-Lopez, A., J. M. C. Plane, A. S. Mahajan, P. S. Anderson, S. J.-B. Bauguitte, A. E. Jones, H. K. Roscoe, R. A. Salmon, W. J. Bloss, J. D. Lee and D. E. Heard

Atmospheric Chemistry and Physics, 8, 887-900, 2008

Abstract. A one-dimensional chemical transport model has been developed to investigate the vertical gradients of bromine and iodine compounds in the Antarctic coastal boundary layer (BL). The model has been applied to interpret recent year-round observations of iodine and bromine monoxides (IO and BrO) at Halley Station, Antarctica. The model requires an equivalent I atom flux of ~1010 molecule cm−2 s−1 from the snowpack in order to account for the measured IO levels, which are up to 20 ppt during spring. Using the current knowledge of gas-phase iodine chemistry, the model predicts significant gradients in the vertical distribution of iodine species. However, recent ground-based and satellite observations of IO imply that the radical is well-mixed in the Antarctic boundary layer, indicating a longer than expected atmospheric lifetime for the radical. This can be modelled by including photolysis of the higher iodine oxides (I2O2, I2O3, I2O4 and I2O5), and rapid recycling of HOI and INO3 through sea-salt aerosol. The model also predicts significant concentrations (up to 25 ppt) of I2O5 in the lowest 10 m of the boundary layer. Heterogeneous chemistry involving sea-salt aerosol is also necessary to account for the vertical profile of BrO. Iodine chemistry causes a large increase (typically more than 3-fold) in the rate of O3 depletion in the BL, compared with bromine chemistry alone. Rapid entrainment of O3 from the free troposphere appears to be required to account for the observation that on occasion there is little O3 depletion at the surface in the presence of high concentrations of IO and BrO. The halogens also cause significant changes to the vertical profiles of OH and HO2 and the NO2/NO ratio. The average Hg0 lifetime against oxidation is also predicted to be about 10 h during springtime. An important result from the model is that very large fluxes of iodine precursors into the boundary layer are required to account for the observed levels of IO. The mechanisms which cause these emissions are unknown. Overall, our results show that halogens profoundly influence the oxidizing capacity of the Antarctic troposphere.



DMS and MSA measurements in the Antarctic boundary layer: impact of BrO on MSA production

Read, K. A., A. C. Lewis, S. Bauguitte, A. M. Rankin, R. A. Salmon, E. W. Wolff, A. Saiz- Lopez, W. J. Bloss, D. E. Heard, J. D. Lee, and J. M. C. Plane

Atmospheric Chemistry and Physics, 8, 2985-2997, 2008

Abstract. In situ measurements of dimethyl sulphide (DMS) and methane sulphonic acid (MSA) were made at Halley Station, Antarctica (75°35' S, 26°19' W) during February 2004–February 2005 as part of the CHABLIS (Chemistry of the Antarctic Boundary Layer and the Interface with Snow) project. DMS was present in the atmosphere at Halley all year (average 38.1±43 pptV) with a maximum monthly average value of 113.6±52 pptV in February 2004 coinciding temporally with a minimum in sea extent. Whilst seasonal variability and interannual variability can be attributed to a number of factors, short term variability appeared strongly dependent on air mass origin and trajectory pressure height. The MSA and derived non-sea salt sulphate (nss-SO42−) measurements showed no correlation with those of DMS (regression R2=0.039, and R2=0.001 respectively) in-line with the complexity of DMS fluxes, alternative oxidation routes, transport of air masses and variable spatial coverage of both sea-ice and phytoplankton. MSA was generally low throughout the year, with an annual average of 42 ng m−3 (9.8±13.2 pptV), however MSA: nss-SO42− ratios were high implying a dominance of the addition oxidation route for DMS. Including BrO measurements into MSA production calculations demonstrated the significance of BrO on DMS oxidation within this region of the atmosphere in austral summer. Assuming an 80% yield of DMSO from the reaction of DMS+BrO, an atmospheric concentration of BrO equal to 3 pptV increased the calculated MSA production from DMS by a factor of 9 above that obtained when considering only reaction with the hydroxyl radical. These findings have significant atmospheric implications, but may also impact on the interpretation of ice cores which previously relied on the understanding of MSA and nss-SO42− chemistry to provide information on environmental conditions such as sea ice extent and the origins of sulphur within the ice.



Chemistry of the Antarctic boundary layer and interface with snow: An overview of the CHABLIS campaign

A. E. Jones, E. W. Wolff, R. A. Salmon, S. J.-B. Bauguitte, H. K. Roscoe, P. S. Anderson, D. Ames, K. C. Clemitshaw, Z. L. Fleming, W. J. Bloss, D. E. Heard, J. D. Lee, K. A. Read, P. Hamer, D. E. Shallcross, A. V. Jackson, S. L. Walker, A. C. Lewis, G. P. Mills, J. M. C. Plane, A. Saiz-Lopez, W. T. Sturges, and D. R. Worton

Atmos. Chem. Phys., 8, 3789-3803, 2008

Abstract. CHABLIS (Chemistry of the Antarctic Boundary Layer and the Interface with Snow) was a collaborative UK research project aimed at probing the detailed chemistry of the Antarctic boundary layer and the exchange of trace gases at the snow surface. The centre-piece to CHABLIS was the measurement campaign, conducted at the British Antarctic Survey station, Halley, in coastal Antarctica, from January 2004 through to February 2005. The campaign measurements covered an extremely wide range of species allowing investigations to be carried out within the broad context of boundary layer chemistry. Here we present an overview of the CHABLIS campaign. We provide details of the measurement location and introduce the Clean Air Sector Laboratory (CASLab) where the majority of the instruments were housed. We describe the meteorological conditions experienced during the campaign and present supporting chemical data, both of which provide a context within which to view the campaign results. Finally we provide a brief summary of highlights from the measurement campaign. Unexpectedly high halogen concentrations profoundly affect the chemistry of many species at Halley throughout the sunlit months, with a secondary role played by emissions from the snowpack. This overarching role for halogens in coastal Antarctic boundary layer chemistry was completely unanticipated, and the results have led to a step-change in our thinking and understanding.



A mechanism for biologically-induced iodine emisiones from sea-ice

Saiz-Lopez, A. and C. S. Boxe

Atmospheric Chemistry and Physics Discussions. 8, 2953-2976, 2008

Abstract. Only recently, ground- and satellite-based measurements have reported high concentrations of IO in coastal Antarctica. The sources of such a large iodine burden in the Antarctic atmosphere remain unknown. We propose a novel mechanism for iodine release from sea-ice surfaces. The release is triggered by the biological production of iodide (I-) and hypoiodous acid (HOI) from marine algae, contained within and underneath sea-ice, and their diffusion through sea-ice brine channels to accumulate in the quasi-liquid layer on the surface of sea-ice. A multiphase chemical model of polar atmospheric chemistry has been developed to investigate the biology-ice-atmosphere coupling in the polar environment. Model simulations were conducted to interpret recent observations of elevated IO in the coastal Antarctic springtime. The results show that the levels of inorganic iodine (i.e. I2, IBr, ICl) released from sea-ice through this mechanism account for the observed IO concentrations in the Antarctic springtime environment. The model results also indicate that iodine may trigger the catalytic release of bromine from sea-ice through phase equilibration of IBr. Considering the extent of sea-ice around the Antarctic continent, we suggest that the resulting high levels of iodine may have widespread impact on catalytic ozone destruction and aerosol formation in the Antarctic lower troposphere.


Extensive halogen-mediated ozone destruction over the sub-tropical Atlantic Ocean

Read, K. A., A. A. Mahajan, L. C. Carpenter, M. J. Evans, B. V. Faria, D. E. Heard, J. R. Hopkins, J. D. Lee, S. Moller, A. C. Lewis, L. Mendes, J. B. McQuaid, H. Oetjen, A. Saiz- Lopez, M. J. Pilling and J. M. C. Plane

Nature, 453, 1232-1235, 2008

Abstract. Increasing tropospheric ozone levels over the past 150 years have led to a significant climate perturbation; the prediction of future trends in tropospheric ozone will require a full understanding of both its precursor emissions and its destruction processes. A large proportion of tropospheric ozone loss occurs in the tropical marine boundary layer and is thought to be driven primarily by high ozone photolysis rates in the presence of high concentrations of water vapour. A further reduction in the tropospheric ozone burden through bromine and iodine emitted from open-ocean marine sources has been postulated by numerical models, but thus far has not been verified by observations. Here we report eight months of spectroscopic measurements at the Cape Verde Observatory indicative of the ubiquitous daytime presence of bromine monoxide and iodine monoxide in the tropical marine boundary layer. A year-round data set of co-located in situ surface trace gas measurements made in conjunction with low-level aircraft observations shows that the mean daily observed ozone loss is approx50 per cent greater than that simulated by a global chemistry model using a classical photochemistry scheme that excludes halogen chemistry. We perform box model calculations that indicate that the observed halogen concentrations induce the extra ozone loss required for the models to match observations. Our results show that halogen chemistry has a significant and extensive influence on photochemical ozone loss in the tropical Atlantic Ocean boundary layer. The omission of halogen sources and their chemistry in atmospheric models may lead to significant errors in calculations of global ozone budgets, tropospheric oxidizing capacity and methane oxidation rates, both historically and in the future.



Variability of the mesospheric nightglow during the 2002 Leonid storms

Plane, J. M. C., A. Saiz-Lopez, B. J. Allan, S. H. Ashworth and P. Jenniskens

Advances in Space Research, 39, 562-566, 2007

Abstract. There was no significant increase in the intensities of three prominent components of the terrestrial nightglow during the 2002 Leonid storm peaks. The atomic oxygen line at 557.7 nm, the sodium D lines at 589.0 and 589.6 nm, and the OH(6,2) band at 826–862 nm were monitored using an airborne spectrometer over the North Atlantic (40–50°N). The results indicate that the meteor storm produced a negligible change in both atomic sodium and oxygen compared to the background concentrations. The spectrometer resolved the sodium doublet, and showed that the ratio of the D2 and D1 lines is not 2.0, as had been thought hitherto, but is highly variable on distances of a few tens of kilometers. The mean value is about 1.8, with values ranging from 1.3 to 2.4.



Seasonal variation of NOx loss processes coupled to the HNO3 formation in a daytime urban atmosphere: a model study

Saiz-Lopez, A., Notario, A., Albaladejo, J. and McFiggans, G.

Water Air and Soil Pollution, 182, 197- 206, 2007

Abstract. We studied the seasonal cycle of the coupling between atmospheric denoxification processes and in-situ daytime formation of gas phase HNO3 using a photochemical air pollution model. The model is constrained with urban atmospheric boundary layer observations of O3, NO2 and NO made in Ciudad Real, central Spain. The highest daytime HNO3 mixing ratio of 0.3 ppbv was predicted to occur in summer, following a modelled OH concentration peak of ∼1.4 × 106 molecules cm−3 and subsequent reaction with NO2. During winter, calculated values of HNO3 are lower due to less incoming radiation and higher wet removal of atmospheric HNO3. The predicted mixing ratios are in good agreement with observations of atmospheric HNO3 at similar urban environments in central Spain. Additionally, a marked seasonal cycle is predicted with minimum HNO3 concentrations occurring in winter, indicative that traffic emissions and photochemistry dominate the in-situ formation of gas phase HNO3 at this location. This process has implications in the removal of NOx from the urban atmosphere.



Night-time radical chemistry during the NAMBLEX campaign

Sommariva, R., S. M. Ball, M. Bitter, W. J. Bloss, Z. L. Fleming, D. E. Heard, R. L. Jones, J. D. Lee, P. S. Monks, M. J. Pilling, J. M. C. Plane and A. Saiz-Lopez

Atmospheric Chemistry and Physics, 7, 587-598, 2007

Abstract. Night-time chemistry in the Marine Boundary Layer has been modelled using a number of observationally constrained zero-dimensional box-models. The models were based upon the Master Chemical Mechanism (MCM) and the measurements were taken during the North Atlantic Marine Boundary Layer Experiment (NAMBLEX) campaign at Mace Head, Ireland in July–September 2002.

The model could reproduce, within the combined uncertainties, the measured concentration of HO2 (within 30–40%) during the night 31 August–1 September and of HO2+RO2 (within 15–30%) during several nights of the campaign. The model always overestimated the NO3 measurements made by Differential Optical Absorption Spectroscopy (DOAS) by up to an order of magnitude or more, but agreed with the NO3 Cavity Ring-Down Spectroscopy (CRDS) measurements to within 30–50%. The most likely explanation of the discrepancy between the two instruments and the model is the reaction of the nitrate radical with inhomogeneously distributed NO, which was measured at concentrations of up to 10 ppt, even though this is not enough to fully explain the difference between the DOAS measurements and the model.

A rate of production and destruction analysis showed that radicals were generated during the night mainly by the reaction of ozone with light alkenes. The cycling between HO2/RO2 and OH was maintained during the night by the low concentrations of NO and the overall radical concentration was limited by slow loss of peroxy radicals to form peroxides. A strong peak in [NO2] during the night 31 August–1 September allowed an insight into the radical fluxes and the connections between the HOx and the NO3 cycles.



First observations of iodine oxide from space

Saiz-Lopez, A., K. Chance, X. Liu, T. P. Kurosu and S. P. Sander

Geophysical Research Letters, 34, L12812, doi:10.1029/2007GL030111

Abstract. We present retrievals of IO total columns from the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) satellite instrument. We analyze data for October 2005 in the polar regions to demonstrate for the first time the capability to measure IO column abundances from space. During the period of analysis (i.e. Southern Hemisphere springtime), enhanced IO vertical columns over 3 × 1013 molecules cm−2 are observed around coastal Antarctica; by contrast during that time in the Artic region IO is consistently below the calculated instrumental detection limit for individual radiance spectra (2–4 × 1012 molecules cm−2 for slant columns). The levels reported here are in reasonably good agreement with previous ground-based measurements at coastal Antarctica. These results also demonstrate that IO is widespread over sea-ice covered areas in the Southern Ocean. The occurrence of elevated IO and its hitherto unrecognized spatial distribution suggest an efficient iodine activation mechanism at a synoptic scale over coastal Antarctica.



Boundary layer halogens in coastal Antarctica

Saiz-Lopez, A., A. S. Mahajan, R. A, Salmon, S. Bauguitte, A. E. Jones, H. K. Roscoe, and J. M. C. Plane

Science, 317, 348-351, 2007

Abstract. Halogens influence the oxidizing capacity of Earth's troposphere, and iodine oxides form ultrafine aerosols, which may have an impact on climate. We report year-round measurements of boundary layer iodine oxide and bromine oxide at the near-coastal site of Halley Station, Antarctica. Surprisingly, both species are present throughout the sunlit period and exhibit similar seasonal cycles and concentrations. The springtime peak of iodine oxide (20 parts per trillion) is the highest concentration recorded anywhere in the atmosphere. These levels of halogens cause substantial ozone depletion, as well as the rapid oxidation of dimethyl sulfide and mercury in the Antarctic boundary layer.



UV-visible Differential Optical Absorption Spectroscopy (DOAS)

J.M.C. Plane and A. Saiz-Lopez

In: D.E. Heard (ed). Analytical Techniques for Atmospheric Measurement. Blackwell Publishing: Oxford, 2006


The North Atlantic Marine Boundary Layer Experiment (NAMBLEX): Overview of the campaign held at Mace Head, Ireland, in summer 2002

D. E. Heard, K. A. Read, J. Methven, S. Al-Haider, W. J. Bloss, G. P. Johnson, M. J. Pilling, P. W. Seakins, S. C. Smith, R. Sommariva, J. C. Stanton, T. J. Still, T. Ingham, B. Brooks, G. De Leeuw, A. V. Jackson, J. B. McQuaid, R. Morgan, M. H. Smith, L. J. Carpenter, N. Carslaw, J. Hamilton, J. R. Hopkins, J. D. Lee, A. C. Lewis, R. M. Purvis, D. J. Wevill, N. Brough, T. Green, G. Mills, S. A. Penkett, J. M. C. Plane, A. Saiz-Lopez, D. Worton, P. S. Monks, Z. Fleming, A. R. Rickard, M. R. Alfarra, J. D. Allan, K. Bower, H. Coe, M. Cubison, M. Flynn, G. McFiggans, M. Gallagher, E. G. Norton, C. D. O'Dowd, J. Shillito, D. Topping, G. Vaughan, P. Williams, M. Bitter, S. M. Ball, R. L. Jones, I. M. Povey, S. O'Doherty, P. G. Simmonds, A. Allen, R. P. Kinnersley, D. C. S. Beddows, M. Dall'Osto, R. M. Harrison, R. J. Donovan, M. R. Heal, S. G. Jennings, C. Noone, and G. Spain

Atmos. Chem. Phys., 6, 2241-2272, 2006

Abstract. The North Atlantic Marine Boundary Layer Experiment (NAMBLEX), involving over 50 scientists from 12 institutions, took place at Mace Head, Ireland (53.32° N, 9.90° W), between 23 July and 4 September 2002. A wide range of state-of-the-art instrumentation enabled detailed measurements of the boundary layer structure and atmospheric composition in the gas and aerosol phase to be made, providing one of the most comprehensive in situ studies of the marine boundary layer to date. This overview paper describes the aims of the NAMBLEX project in the context of previous field campaigns in the Marine Boundary Layer (MBL), the overall layout of the site, a summary of the instrumentation deployed, the temporal coverage of the measurement data, and the numerical models used to interpret the field data. Measurements of some trace species were made for the first time during the campaign, which was characterised by predominantly clean air of marine origin, but more polluted air with higher levels of NOx originating from continental regions was also experienced. This paper provides a summary of the meteorological measurements and Planetary Boundary Layer (PBL) structure measurements, presents time series of some of the longer-lived trace species (O3, CO, H2, DMS, CH4, NMHC, NOx, NOy, PAN) and summarises measurements of other species that are described in more detail in other papers within this special issue, namely oxygenated VOCs, HCHO, peroxides, organo-halogenated species, a range of shorter lived halogen species (I2, OIO, IO, BrO), NO3 radicals, photolysis frequencies, the free radicals OH, HO2 and (HO2+Σ RO2), as well as a summary of the aerosol measurements. NAMBLEX was supported by measurements made in the vicinity of Mace Head using the NERC Dornier-228 aircraft. Using ECMWF wind-fields, calculations were made of the air-mass trajectories arriving at Mace Head during NAMBLEX, and were analysed together with both meteorological and trace-gas measurements. In this paper a chemical climatology for the duration of the campaign is presented to interpret the distribution of air-mass origins and emission sources, and to provide a convenient framework of air-mass classification that is used by other papers in this issue for the interpretation of observed variability in levels of trace gases and aerosols.



The mass balance of mercury in the springtime polar environment

Brooks, S. B., A. Saiz-Lopez, H. Skov, S. E. Lindberg, J. M. C. Plane and M. E. Goodsite

Geophysical Research Letters, 33, L13812, doi:10.1029/2005GL025525, 2006

Abstract. The load of mercury in the Arctic environment is to a large extent controlled by atmospheric mercury depletion events. At Barrow, Alaska, these depletion events have been linked with the near-surface air formation of reactive gaseous mercury (Hg(II)) (RGM), to a much lesser extent in a particulate-bound form, and the accumulation of total mercury in the snow pack (>100 ng/L in late Spring). This transport of Hg from atmospheric conversion, to deposition, to bio-available forms is likely to be the predominant pathway for mercury into Arctic biota. For the first time we combine flux rate measurements, atmospheric chemistry measurements, and air mass trajectories to give a comprehensive two-week window into the springtime dynamics and mass balance of Arctic mercury. We have conducted polar-sunrise to snowmelt mercury monitoring at Barrow from 1998 to 2004, and the time period March 25th–April 7th (Julian days 84–97), 2003 appears typical for this time of year. A clear link was observed between air of marine origin, the build-up of BrO together with removal of gaseous elemental mercury (GEM)), and the formation of RGM. This provides the most direct evidence so far for Br and Hg chemistry as the direct source of RGM. The fluxes of RGM and GEM were determined and the net flux calculated.



Seasonal evolution of levels of gaseous pollutants in an urban area (Ciudad Real) in central-southern Spain: a DOAS study

Saiz-Lopez, A., A. Notario, E. Martinez and J. Albaladejo

Water Air and Soil Pollution, 171, 153-167, 2006


Abstract. Long term continuous monitoring measurements of urban atmospheric concentrations of O3, NO2, NO, and SO2 were performed for the first time in Ciudad Real, a city in central-southern Spain. The measurements were carried out using the differential optical absorption spectroscopy (DOAS) technique, with a commercial system (OPSIS, Lund-Sweden), covering the summer and winter seasons (from 21st July 2000 to 23rd March 2001). Mean levels of O3, NO2 and SO2 monitored during this period were: 27 μg m−3, 50 μg m−3 and 7 μg m−3 respectively. The highest hourly averaged value of O3 (160 μg m−3) was measured during the summer period, while NO2 was enhanced in wintertime (highest values 90 μg m−3). In the coldest period, when central heating installations were operating, SO2 showed maximum levels of 20 μg m−3. The daily, weekly and seasonal analysis of the data shows that photochemical air pollution dominates in this urban atmosphere and is strongly influenced by levels of motor traffic and domestic heating system emissions. These measurements were compared with other studies in Spain and Europe. Also, the long path averaged DOAS measurements were compared with in situ observations made in Ciudad Real, from 23rd August 2000 to 25th September 2000, using a mobile air pollution control station. All gas concentrations reported in this paper are below the WHO guidelines and the different thresholds introduced by the European Environmental Legislation.



Peroxy radical chemistry and the control of ozone photochemistry at Mace Head, Ireland during the summer of 2002

Fleming, Z. L, P. S. Monks, A. R. Rickard, D. E. Heard, W. J. Bloss, P. I. Seakins, T. J. Still, R. Sommariva, M. J. Pilling, R. Morgan, T. J. Green, N. Brough, S. A. Penkett, A. C. Lewis, J. D. Lee, A. Saiz-Lopez and J. M. C. Plane

Atmos. Chem. Phys., 6, 2193-2214, 2006

Abstract. Peroxy radical (HO2+ΣRO2) measurements, using the PEroxy Radical Chemical Amplification (PERCA) technique at the North Atlantic Marine Boundary Layer EXperiment (NAMBLEX) at Mace Head in summer 2002, are presented and put into the context of marine, boundary-layer chemistry. A suite of other chemical parameters (NO, NO2, NO3, CO, CH4, O3, VOCs, peroxides), photolysis frequencies and meteorological measurements, are used to present a detailed analysis of the role of peroxy radicals in tropospheric oxidation cycles and ozone formation. Under the range of conditions encountered the peroxy radical daily maxima varied from 10 to 40 pptv. The diurnal cycles showed an asymmetric shape typically shifted to the afternoon. Using a box model based on the master chemical mechanism the average model measurement agreement was 2.5 across the campaign. The addition of halogen oxides to the model increases the level of model/measurement agreement, apparently by respeciation of HOx. A good correlation exists between j(HCHO).[HCHO] and the peroxy radicals indicative of the importance of HCHO in the remote atmosphere as a HOx source, particularly in the afternoon. The peroxy radicals showed a strong dependence on [NO2] with a break point at 0.1 ppbv, where the radicals increased concomitantly with the reactive VOC loading, this is a lower value than seen at representative urban campaigns. The HO2/(HO2+ΣRO2) ratios are dependent on [NOx] ranging between 0.2 and 0.6, with the ratio increasing linearly with NOx. Significant night-time levels of peroxy radicals were measured up to 25 pptv. The contribution of ozone-alkenes and NO3-alkene chemistry to night-time peroxy radical production was shown to be on average 59 and 41%. The campaign mean net ozone production rate was 0.11±0.3 ppbv h-1. The ozone production rate was strongly dependent on [NO] having linear sensitivity (dln(P(O3))/dln(NO)=1.0). The results imply that the N(O3) (the in-situ net photochemical rate of ozone production/destruction) will be strongly sensitive in the marine boundary layer to small changes in [NO] which has ramifications for changing NOx loadings in the European continental boundary layer.



Modelling the molecular iodine emissions at coastal marine environments: the link to new particle formation

Saiz-Lopez, A., J. M.C. Plane, G. McFiggans, P. I. Williams, S. M. Ball, M. Bitter, R. L. Jones, C. Hongwei and T. Hoffmann

Atmospheric Chemistry and Physics, 6, 883-895, 2006

Abstract. A model of iodine chemistry in the marine boundary layer (MBL) has been used to investigate the impact of daytime coastal emissions of molecular iodine (I2). The model contains a full treatment of gas-phase iodine chemistry, combined with a description of the nucleation and growth, by condensation and coagulation, of iodine oxide nano-particles. In-situ measurements of coastal emissions of I2 made by the broadband cavity ring-down spectroscopy (BBCRDS) and inductively coupled plasma-mass spectrometry (ICP/MS) techniques are presented and compared to long path differential optical absorption spectroscopy (DOAS) observations of I2 at Mace Head, Ireland. Simultaneous measurements of enhanced I2 emissions and particle bursts show that I2 is almost certainly the main precursor of new particles at this coastal location. The ratio of IO to I2 predicted by the model indicates that the iodine species observed by the DOAS are concentrated over a short distance (about 8% of the 4.2 km light path) consistent with the intertidal zone, bringing them into good agreement with the I2 measurements made by the two in-situ techniques. The model is then used to investigate the effect of iodine emission on ozone depletion, and the production of new particles and their evolution to form stable cloud condensation nuclei (CCN).



Measurements and modelling of I2, IO, OIO, BrO and NO3 in the mid-latitude marine boundary layer

Saiz-Lopez, A., J. A. Shillito, H. Coe and J. M. C. Plane

Atmospheric Chemistry and Physics, 6, 1513-1528, 2006

Abstract. Time series observations of molecular iodine (I2), iodine oxides (IO, OIO), bromine oxide (BrO), and the nitrate radical (NO3) in the mid-latitude coastal marine boundary layer (MBL) are reported. Measurements were made using a new long-path DOAS instrument during a summertime campaign at Mace Head on the B3Π(0+u)-X1Σ+g electronic transition between 535 and 575 nm. The I2 mixing ratio was found to vary from below the detection limit (~5 ppt) up to a nighttime maximum of 93 ppt. Along with I2, observations of IO, OIO and NO3 were also made during the night. Surprisingly, IO and OIO were detected at mixing ratios up to 2.5 and 10.8 ppt, respectively. A model is employed to show that the reaction between I2 and NO3 is the likely nighttime source of these radicals. The BrO mixing ratio varied from below the detection limit at night (~1 ppt) to a maximum of 6 ppt in the first hours after sunrise. A bromine chemistry model is used to simulate the diurnal behaviour of the BrO radical, demonstrating the importance of halogen recycling through sea-salt aerosol. In the same campaign a zenith sky DOAS was employed to determine the column density variation of NO3 as a function of solar zenith angle (SZA) during sunrise, from which vertical profiles of NO3 through the troposphere were obtained. On several occasions a positive gradient of NO3 was observed over the first 2 km, possibly due to dimethyl sulphide (DMS) removing NO3 at the ocean surface.



OH and HO2 chemistry during NAMBLEX: roles of oxygenates, halogen oxides and heterogeneous uptake

Sommariva, R., W. J. Bloss, N. Brough, N. Carslaw, M. Flynn, A.-L. Haggerstone, D. E. Heard, J. R. Hopkins, J. D. Lee, A. C. Lewis, G. McFiggans, P. S. Monks, S. A. Penkett, M. J. Pilling, J. M. C. Plane, K. A Read, A. R. Rickard, A. Saiz-Lopez and P. I. Williams

Atmos. Chem. Phys., 6, 1135-1153, 2006

Abstract. Several zero-dimensional box-models with different levels of chemical complexity, based on the Master Chemical Mechanism (MCM), have been used to study the chemistry of OH and HO2 in a coastal environment in the Northern Hemisphere. The models were constrained to and compared with measurements made during the NAMBLEX campaign (Mace Head, Ireland) in summer 2002.

The base models, which were constrained to measured CO, CH4 and NMHCs, were able to reproduce [OH] within 25%, but overestimated [HO2] by about a factor of 2. Agreement was improved when the models were constrained to oxygenated compounds (acetaldehyde, methanol and acetone), highlighting their importance for the radical budget. When the models were constrained to measured halogen monoxides (IO, BrO) and used a more detailed, measurements-based, treatment to describe the heterogeneous uptake, modelled [OH] increased by up to 15% and [HO2] decreased by up to 30%. The actual impact of halogen monoxides on the modelled concentrations of HOx was dependant on the uptake coefficients used for HOI, HOBr and HO2. Better agreement, within the combined uncertainties of the measurements and of the model, was achieved when using high uptake coefficients for HO2 and HOI (γHO2=1, γHOI=0.6).

A rate of production and destruction analysis of the models allowed a detailed study of OH and HO2 chemistry under the conditions encountered during NAMBLEX, showing the importance of oxygenates and of XO (where X=I, Br) as co-reactants for OH and HO2 and of HOX photolysis as a source for OH.



Impact of halogen monoxide chemistry upon boundary layer OH and HO2 concentrations at a coastal site

W.J. Bloss, J.D. Lee, G.P. Johnson, R. Sommariva, D.E. Heard, A. Saiz-Lopez, J.M.C. Plane, A. Rickard, Z. Fleming,G. McFiggans, H. Coe, M. Flynn and P. Williams

Geophysical Research Letters, 32, L06814, doi: 10.1029/2004GL022084, 2005

Abstract. The impact of iodine oxide chemistry upon OH and HO2 concentrations in the coastal marine boundary layer has been evaluated using data from the NAMBLEX (North Atlantic Marine Boundary Layer Experiment) campaign, conducted at Mace Head, Ireland during the summer of 2002. Observationally constrained calculations show that under low NOx conditions experienced during NAMBLEX (NO ≤ 50 pptv), the reaction IO + HO2 → HOI + O2 accounted for up to 40% of the total HO2 radical sink, and the subsequent photolysis of HOI to form OH + I comprised up to 15% of the total midday OH production rate. The XO + HO2 (X = Br, I) reactions may in part account for model overestimates of measured HO2 concentrations in previous studies at Mace Head, and should be considered in model studies of HOx chemistry at similar coastal locations.



Variability of the mesospheric nightglow sodium D2/D1 ratio

Slanger, T. G., P. C. Cosby, D. L. Huestis, A. Saiz-Lopez, B. J. Murray, D. A. O'Sullivan, J. M. C. Plane, C. Allende Prieto, F. J. Martin-Torres, and P. Jenniskens

Journal of Geophysical Research,110, D23302, doi:10.1029/2005JD006078. 2005

Abstract. Measurements of the intensity ratio of the 589.0/589.6 nm sodium doublet in the terrestrial nightglow over an 8-year period, involving >300 separate determinations, have established that it is variable, the value RD = I(D2)/I(D1) lying between 1.2 and 1.8. Sky spectra from the Keck I telescope with the High-Resolution Échelle Spectrometer (HIRES) échelle spectrograph and the Keck II telescope with the Échellette Spectrograph and Imager (ESI) échelle spectrograph were used in this analysis. The result contrasts with the accepted view, from earlier measurements at midlatitude, that the ratio is 2.0, as expected on statistical grounds. The lack of dependence of the ratio on viewing elevation angle, and hence Na slant column, allows self-absorption to be ruled out as a cause of the variability. The data suggest a semiannual oscillation in the ratio, maximum at the equinoxes and minimum at the solstices. Airborne measurements over the North Atlantic (40°–50°N) in 2002 show an even larger range in the nightglow ratio and no correlation with the upper mesospheric temperature determined from the OH 6–2 bands. A laboratory study confirms that the ratio does not depend on temperature; however, it is shown to be sensitive to the [O]/[O2] ratio. It is therefore postulated that the variable ratio arises from a competition between O reacting with NaO(A3Σ+), produced from the reaction of Na with O3, to yield D-line emission with a D2/D1 ratio greater than about 2.0, and quenching by O2 to produce NaO(X2Π), possibly with vibrational excitation, which then reacts with O to produce emission with a ratio of less than 1.3.



Recent applications of Differential Optical Absorption Spectroscopy: halogen chemistry in the lower troposphere

Saiz-Lopez, A. and J.M.C. Plane

J. Phys. IV France 121 (2004) 223-238

Abstract. This chapter provides a comprehensive review of the atmospheric chemistry of halogens in the lower troposphere, including a discussion of the important ways in which halogens affect this region of the atmosphere. It then describes the recent progress made in observing these species by the Differential Optical Absorption Spectroscopy (DOAS) technique. A brief description of the technique and its capabilities is also provided.



Direct evidence for coastal iodine particles from Laminaria macroalgae – linkage to emissions of molecular iodine

G. McFiggans, H. Coe, R. Burgess, J. Allan, M. Cubison, M. R. Alfarra, R. Saunders, A. Saiz-Lopez, J. M. C. Plane, D. Wevill, L. Carpenter, A. R. Rickard, and P. S. Monks

Atmos. Chem. Phys., 4, 701-713, 2004

Abstract. Renewal of ultrafine aerosols in the marine boundary layer may lead to repopulation of the marine distribution and ultimately determine the concentration of cloud condensation nuclei (CCN). Thus the formation of nanometre-scale particles can lead to enhanced scattering of incoming radiation and a net cooling of the atmosphere. The recent demonstration of the chamber formation of new particles from the photolytic production of condensable iodine-containing compounds from diiodomethane (CH2I2), (O'Dowd et al., 2002; Kolb, 2002; Jimenez et al., 2003a; Burkholder and Ravishankara, 2003), provides an additional mechanism to the gas-to-particle conversion of sulphuric acid formed in the photo-oxidation of dimethylsulphide for marine aerosol repopulation. CH2I2 is emitted from seaweeds (Carpenter et al., 1999, 2000) and has been suggested as an initiator of particle formation. We demonstrate here for the first time that ultrafine iodine-containing particles are produced by intertidal macroalgae exposed to ambient levels of ozone. The particle composition is very similar both to those formed in the chamber photo-oxidation of diiodomethane and in the oxidation of molecular iodine by ozone. The particles formed in all three systems are similarly aspherical. When small, those formed in the molecular iodine system swell only moderately when exposed to increased humidity environments, and swell progressively less with increasing size; this behaviour occurs whether they are formed in dry or humid environments, in contrast to those in the CH2I2 system. Direct coastal boundary layer observations of molecular iodine, ultrafine particle production and iodocarbons are reported. Using a newly measured molecular iodine photolysis rate, it is shown that, if atomic iodine is involved in the observed particle bursts, it is of the order of at least 1000 times more likely to result from molecular iodine photolysis than diiodomethane photolysis. A hypothesis for molecular iodine release from intertidal macroalgae is presented and the potential importance of macroalgal iodine particles in their contribution to CCN and global radiative forcing are discussed.



Absolute absorption cross-section and photolysis rate of I2

A. Saiz-Lopez, R. W. Saunders, D. M. Joseph, S. H. Ashworth, and J. M. C. Plane

Atmos. Chem. Phys., 4, 1443-1450, 2004

Abstract. Following recent observations of molecular iodine (I2) in the coastal marine boundary layer (MBL) (Saiz-Lopez and Plane, 2004), it has become important to determine the absolute absorption cross-section of I2 at reasonably high resolution, and also to evaluate the rate of photolysis of the molecule in the lower atmosphere. The absolute absorption cross-section (σ) of gaseous I2 at room temperature and pressure (295K, 760Torr) was therefore measured between 182 and 750nm using a Fourier Transform spectrometer at a resolution of 4cm-1 (0.1nm at λ=500nm). The maximum absorption cross-section in the visible region was observed at λ=533.0nm to be σ=(4.24±0.50)x10-18cm2molecule-1. The spectrum is available as supplementary material accompanying this paper. The photo-dissociation rate constant (J) of gaseous I2 was also measured directly in a solar simulator, yielding J(I2)=0.12±0.03s-1 for the lower troposphere. This is in excellent agreement with the value of 0.12±0.015s-1 calculated using the measured absorption cross-section, terrestrial solar flux for clear sky conditions and assuming a photo-dissociation yield of unity. A two-stream radiation transfer model was then used to determine the variation in photolysis rate with solar zenith angle (SZA), from which an analytic expression is derived for use in atmospheric models. Photolysis appears to be the dominant loss process for I2 during daytime, and hence an important source of iodine atoms in the lower atmosphere.



Novel iodine chemistry in the marine boundary layer

Alfonso Saiz-Lopez, John M.C. Plane

Geophysical Research Letters, 31, L04112, doi: 10.1029/2003GL019215, 2004

Abstract. The atmospheric chemistry of iodine is important for several reasons, including the influence of iodine oxides on the oxidising capacity of the troposphere, the formation of new particles, and the enrichment of iodine in marine aerosols and the transport of this essential dietary element to the continents. It is shown here that a substantial iodine source is I2, most likely emitted from macro-algae at low tide. This source accounts for the daytime production of new particles in the coastal marine boundary layer, and also explains the discovery of significant night-time levels of iodine oxides.



Bromine oxide in the mid-latitude marine boundary layer

Saiz-Lopez, A., J.M.C. Plane and J. A. Shillito

Geophysical Research Letters, 31, LO3111, doi: 10.1029/2003GL018956, 2004

Abstract. We report direct observations of bromine oxide (BrO) in the mid-latitude marine boundary layer (MBL), using long-path Differential Optical Absorption Spectroscopy (DOAS). The measurements were made at the Mace Head observatory on the west coast of Ireland. Over six days of observations, the BrO concentration varied from below the detection limit (≈0.8 parts per trillion (ppt)) at night, to a maximum daytime concentration of 6.5 ppt. At the average daytime concentration of 2.3 ppt, BrO causes significant O3 depletion in the MBL through catalytic cycles involving the iodine oxide and hydroperoxy radicals, and also oxidises dimethyl sulfide much more rapidly than the hydroxyl radical. A post-sunrise pulse of BrO was observed, consistent with the build up of photolabile precursors produced by heterogeneous reactions on sea-salt aerosol during the previous night. This indicates that significant bromine activation occurs over the open ocean.


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