Global tropospheric halogen (Cl, Br, I) chemistry and its impact on oxidants

We present an updated mechanism for tropospheric halogen (Cl&thinsp;+&thinsp;Br&thinsp;+&thinsp;I) chemistry in the GEOS-Chem global atmospheric chemical transport model and apply it to investigate halogen radical cycling and implications for tropospheric oxidants. Improved representation of HOBr heterogeneous chemistry and its pH dependence in our simulation leads to less efficient recycling and mobilization of bromine radicals and enables the model to include mechanistic sea salt aerosol debromination without generating excessive BrO. The resulting global mean tropospheric BrO mixing ratio is 0.19&thinsp;ppt (parts per trillion), lower than previous versions of GEOS-Chem. Model BrO shows variable consistency and biases in comparison to surface and aircraft observations in marine air, which are often near or below the detection limit. The model underestimates the daytime measurements of Cl2 and BrCl from the ATom aircraft campaign over the Pacific and Atlantic, which if correct would imply a very large missing primary source of chlorine radicals. Model IO is highest in the marine boundary layer and uniform in the free troposphere, with a global mean tropospheric mixing ratio of 0.08&thinsp;ppt, and shows consistency with surface and aircraft observations. The modeled global mean tropospheric concentration of Cl atoms is 630&thinsp;cm&minus;3, contributing 0.8&thinsp;% of the global oxidation of methane, 14&thinsp;% of ethane, 8&thinsp;% of propane, and 7&thinsp;% of higher alkanes. Halogen chemistry decreases the global tropospheric burden of ozone by 11&thinsp;%, NOx by 6&thinsp;%, and OH by 4&thinsp;%. Most of the ozone decrease is driven by iodine-catalyzed loss. The resulting GEOS-Chem ozone simulation is unbiased in the Southern Hemisphere but too low in the Northern Hemisphere. &nbsp; Full List of Authors: Xuan Wang1,2, Daniel J. Jacob3, William Downs3, Shuting Zhai4, Lei Zhu5, Viral Shah3, Christopher D. Holmes6, Tom&aacute;s Sherwen7,8, Becky Alexander4, Mathew J. Evans7,8, Sebastian D. Eastham9, J. Andrew Neuman10,11, Patrick R. Veres10, Theodore K. Koenig11,12, Rainer Volkamer11,12, L. Gregory Huey13, Thomas J. Bannan14, Carl J. Percival14,a, Ben H. Lee4, and Joel A. Thornton4 1School of Energy and Environment, City University of Hong Kong, Hong Kong SAR, China 2City University of Hong Kong Shenzhen Research Institute, Shenzhen, China 3School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA 4Department of Atmospheric Sciences, University of Washington, Seattle, Washington, USA 5School of Environmental Science and Engineering, Southern University of Science and Technology, Shenzhen, China 6Department of Earth, Ocean, and Atmospheric Science, Florida State University, Tallahassee, Florida, USA 7Wolfson Atmospheric Chemistry Laboratories, Department of Chemistry, University of York, York, UK 8National Centre for Atmospheric Science, University of York, York, UK 9Laboratory for Aviation and the Environment, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA 10NOAA Chemical Sciences Laboratory (CSL), Boulder, Colorado, USA 11Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA 12Department of Chemistry, University of Colorado, Boulder, Colorado, USA 13School of Earth and Atmospheric Science, Georgia Institute of Technology, Atlanta, Georgia, USA 14School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, UK anow at: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA &nbsp;</p

The driving factors of new particle formation and growth in the polluted boundary layer

New particle formation (NPF) is a significant source of atmospheric particles, affecting climate and air quality. Understanding the mechanisms involved in urban aerosols is important to develop effective mitigation strategies. However, NPF rates reported in the polluted boundary layer span more than 4 orders of magnitude, and the reasons behind this variability are the subject of intense scientific debate. Multiple atmospheric vapours have been postulated to participate in NPF, including sulfuric acid, ammonia, amines and organics, but their relative roles remain unclear. We investigated NPF in the CLOUD chamber using mixtures of anthropogenic vapours that simulate polluted boundary layer conditions. We demonstrate that NPF in polluted environments is largely driven by the formation of sulfuric acid&ndash;base clusters, stabilized by the presence of amines, high ammonia concentrations and lower temperatures. Aromatic oxidation products, despite their extremely low volatility, play a minor role in NPF in the chosen urban environment but can be important for particle growth and hence for the survival of newly formed particles. Our measurements quantitatively account for NPF in highly diverse urban environments and explain its large observed variability. Such quantitative information obtained under controlled laboratory conditions will help the interpretation of future ambient observations of NPF rates in polluted atmospheres. Full List of Authors: Mao Xiao1, Christopher R. Hoyle1,2, Lubna Dada3, Dominik Stolzenburg4, Andreas K&uuml;rten5, Mingyi Wang6, Houssni Lamkaddam1, Olga Garmash3, Bernhard Mentler7, Ugo Molteni1, Andrea Baccarini1, Mario Simon5, Xu-Cheng He3, Katrianne Lehtipalo3,8, Lauri R. Ahonen3, Rima Baalbaki3, Paulus S. Bauer4, Lisa Beck3, David Bell1, Federico Bianchi3, Sophia Brilke4, Dexian Chen6, Randall Chiu9, Ant&oacute;nio Dias10, Jonathan Duplissy3,11, Henning Finkenzeller9, Hamish Gordon6, Victoria Hofbauer6, Changhyuk Kim13,14, Theodore K. Koenig9,a, Janne Lampilahti3, Chuan Ping Lee1, Zijun Li15, Huajun Mai13, Vladimir Makhmutov16, Hanna E. Manninen17, Ruby Marten1, Serge Mathot17, Roy L. Mauldin18,19, Wei Nie20, Antti Onnela17, Eva Partoll7, Tuukka Pet&auml;j&auml;3, Joschka Pfeifer5,17, Veronika Pospisilova1, Lauriane L. J. Qu&eacute;l&eacute;ver3, Matti Rissanen3,b, Siegfried Schobesberger15, Simone Schuchmann17,c, Yuri Stozhkov16, Christian Tauber4, Yee Jun Tham3, Ant&oacute;nio Tom&eacute;21, Miguel Vazquez-Pufleau4, Andrea C. Wagner5,9,d, Robert Wagner3, Yonghong Wang3, Lena Weitz5, Daniela Wimmer3,4, Yusheng Wu3, Chao Yan3, Penglin Ye6,22, Qing Ye6, Qiaozhi Zha3, Xueqin Zhou5, Antonio Amorim10, Ken Carslaw12, Joachim Curtius5, Armin Hansel7, Rainer Volkamer9,19, Paul M. Winkler4, Richard C. Flagan13, Markku Kulmala3,11,20,23, Douglas R. Worsnop3,22, Jasper Kirkby5,17, Neil M. Donahue6, Urs Baltensperger1, Imad El Haddad1, and Josef Dommen1 1Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland 2Institute for Atmospheric and Climate Science, ETH Zurich, 8092 Zurich, Switzerland 3Institute for Atmospheric and Earth System Research (INAR)/Physics, University of Helsinki, 00014 Helsinki, Finland 4Faculty of Physics, University of Vienna, 1090 Vienna, Austria 5Institute for Atmospheric and Environmental Sciences, Goethe University Frankfurt, 60438 Frankfurt am Main, Germany 6Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA 15213, USA 7Institute of Ion Physics and Applied Physics, University of Innsbruck, 6020 Innsbruck, Austria 8Atmospheric Composition Research Unit, Finnish Meteorological Institute, 00560 Helsinki, Finland 9Department of Chemistry &amp; CIRES, University of Colorado Boulder, Boulder, CO 80309, USA 10CENTRA and FCUL, University of Lisbon, 1749-016 Lisbon, Portugal 11Helsinki Institute of Physics, University of Helsinki, 00014 Helsinki, Finland 12School of Earth and Environment, University of Leeds, LS2 9JT Leeds, United Kingdom 13Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA 14School of Civil and Environmental Engineering, Pusan National University, 46241 Busan, Republic of Korea 15Department of Applied Physics, University of Eastern Finland, 70211 Kuopio, Finland 16Solar and Cosmic Ray Physics Laboratory, P.N. Lebedev Physical Institute of the Russian Academy of Sciences, 119991 Moscow, Russian Federation 17CERN, 1211 Geneva, Switzerland 18Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA 15213, USA 19Department of Oceanic and Atmospheric Sciences, University of Colorado Boulder, Boulder, CO 80309, USA 20Joint International Research Laboratory of Atmospheric and Earth System Sciences, School of Atmospheric Sciences, Nanjing University, Nanjing, Jiangsu Province, China 21IDL-Universidade da Beira Interior, Covilh&atilde;, Portugal 22Aerodyne Research Inc., Billerica, MA 01821-3976, USA 23Aerosol and Haze Laboratory, Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing University of Chemical Technology, Beijing, China anow at: College of Environmental Sciences and Engineering, Peking University, 100871 Beijing, China bnow at: Aerosol Physics Laboratory, Physics Unit, Faculty of Engineering and Natural Sciences, Tampere University, 33720 Tampere, Finland cnow at: Experimentelle Teilchen- und Astroteilchenphysik, Johannes Gutenberg University Mainz, 55128 Mainz, Germany dnow at: Department of Chemistry &amp; CIRES, University of Colorado Boulder, Boulder, CO 80305, USA Correspondence: Urs Baltensperger ([email protected]) and Imad El Haddad ([email protected])</p

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

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 3ĝ€¯%-4ĝ€¯% reduction in the ozone column, which is greatest at high latitudes. The model indicates the strongest influence of iodine in the lower stratosphere with 30ĝ€¯ppbv less ozone at low latitudes and up to 100ĝ€¯ppbv less at high latitudes. In the troposphere, the account of the iodine chemistry reduces the tropospheric ozone concentration by 5ĝ€¯%-10ĝ€¯% depending on geographical location. In the lower troposphere, 75ĝ€¯% of the modeled ozone reduction originates from inorganic sources of iodine, 25ĝ€¯% from organic sources of iodine. At 50ĝ€¯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 1.5ĝ€¯%-2.5ĝ€¯%. 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.Fil: Karagodin Doyennel, Arseniy. The Institute for Atmospheric and Climate Science; Suiza. Physikalisch-Meteorologisches Observatorium Davos/World Radiation Center; SuizaFil: Rozanov, Eugene. The Institute for Atmospheric and Climate Science; Suiza. Physikalisch-Meteorologisches Observatorium Davos/World Radiation Center; Suiza. Saint Petersburg State University; RusiaFil: Sukhodolov, Timofei. Physikalisch-Meteorologisches Observatorium Davos/World Radiation Center; Suiza. Saint Petersburg State University; Rusia. University of Natural Resources and Life Sciences; AustriaFil: Egorova, Tatiana. Physikalisch-Meteorologisches Observatorium Davos/World Radiation Center; SuizaFil: Saiz López, Alfonso. Consejo Superior de Investigaciones Científicas. Instituto de Química Física; EspañaFil: Cuevas, Carlos A.. Consejo Superior de Investigaciones Científicas. Instituto de Química Física; EspañaFil: Fernandez, Rafael Pedro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Interdisciplinario de Ciencias Básicas. - Universidad Nacional de Cuyo. Instituto Interdisciplinario de Ciencias Básicas; Argentina. Consejo Superior de Investigaciones Científicas. Instituto de Química Física; EspañaFil: Sherwen, Tomás. University of York; Reino UnidoFil: Volkamer, Rainer. The Institute for Atmospheric and Climate Science ; Suiza. State University of Colorado at Boulder; Estados Unidos. Cooperative Institute for Research in Environmental Sciences; Estados Unidos. Paul Scherrer Institute; SuizaFil: Koenig, Theodore K.. State University of Colorado at Boulder; Estados Unidos. Cooperative Institute for Research in Environmental Sciences; Estados UnidosFil: Giroud, Tanguy. The Institute for Atmospheric and Climate Science; SuizaFil: Peter, Thomas. The Institute for Atmospheric and Climate Science; Suiz

Observed in-plume gaseous elemental mercury depletion suggests significant mercury scavenging by volcanic aerosols

Terrestrial volcanism is known to emit mercury (Hg) into the atmosphere. However, despite many years of investigation, its net impact on the atmospheric Hg budget remains insufficiently constrained, in part because the transformations of Hg in volcanic plumes as they age and mix with background air are poorly understood. Here we report the observation of complete gaseous elemental mercury (GEM) depletion events in dilute and moderately aged (&amp; SIM;3-7 hours) volcanic plumes from Piton de la Fournaise on Reunion Island. While it has been suggested that co-emitted bromine could, once photochemically activated, deplete GEM in a volcanic plume, we measured low bromine concentrations in both the gas- and particle-phase and observed complete GEM depletion even before sunrise, ruling out a leading role of bromine chemistry here. Instead, we hypothesize that the GEM depletions were mainly caused by gas-particle interactions with sulfate-rich volcanic particles (mostly of submicron size), abundantly present in the dilute plume. We consider heterogeneous GEM oxidation and GEM uptake by particles as plausible manifestations of such a process and derive empirical rate constants. By extrapolation, we estimate that volcanic aerosols may scavenge 210 Mg y(-1) (67-480 Mg y(-1)) of Hg from the atmosphere globally, acting effectively as atmospheric mercury sink. While this estimate is subject to large uncertainties, it highlights that Hg transformations in aging volcanic plumes must be better understood to determine the net impact of volcanism on the atmospheric Hg budget and Hg deposition pathways

Precursors and Pathways Leading to Enhanced Secondary Organic Aerosol Formation during Severe Haze Episodes

Publisher Copyright: © 2021 American Chemical SocietyMolecular analyses help to investigate the key precursors and chemical processes of secondary organic aerosol (SOA) formation. We obtained the sources and molecular compositions of organic aerosol in PM2.5in winter in Beijing by online and offline mass spectrometer measurements. Photochemical and aqueous processing were both involved in producing SOA during the haze events. Aromatics, isoprene, long-chain alkanes or alkenes, and carbonyls such as glyoxal and methylglyoxal were all important precursors. The enhanced SOA formation during the severe haze event was predominantly contributed by aqueous processing that was promoted by elevated amounts of aerosol water for which multifunctional organic nitrates contributed the most followed by organic compounds having four oxygen atoms in their formulae. The latter included dicarboxylic acids and various oxidation products from isoprene and aromatics as well as products or oligomers from methylglyoxal aqueous uptake. Nitrated phenols, organosulfates, and methanesulfonic acid were also important SOA products but their contributions to the elevated SOA mass during the severe haze event were minor. Our results highlight the importance of reducing nitrogen oxides and nitrate for future SOA control. Additionally, the formation of highly oxygenated long-chain molecules with a low degree of unsaturation in polluted urban environments requires further research.Peer reviewe

Quantitative detection of iodine in the stratosphere

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. Gasphase 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.Fil: Koenig, Theodore K.. State University of Colorado at Boulder; Estados UnidosFil: Baidar, Sunil. State University of Colorado at Boulder; Estados UnidosFil: Campuzano Jost, Pedro. State University of Colorado at Boulder; Estados UnidosFil: Cuevas, Carlos Alberto. Consejo Superior de Investigaciones Científicas. Instituto de Química Física; EspañaFil: Dix, Barbara. State University of Colorado at Boulder; Estados UnidosFil: Fernandez, Rafael Pedro. Consejo Superior de Investigaciones Científicas. Instituto de Química Física; España. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Interdisciplinario de Ciencias Básicas. - Universidad Nacional de Cuyo. Instituto Interdisciplinario de Ciencias Básicas; ArgentinaFil: Guo, Hongyu. State University of Colorado at Boulder; Estados UnidosFil: Hall, Samuel R.. National Center for Atmospheric Research; Estados UnidosFil: Kinnison, Douglas. National Center for Atmospheric Research; Estados UnidosFil: Nault, Benjamin A.. State University of Colorado at Boulder; Estados UnidosFil: Ullmann, Kirk. National Center for Atmospheric Research; Estados UnidosFil: Jimenez, Jose L.. State University of Colorado at Boulder; Estados UnidosFil: Saiz López, Alfonso. Consejo Superior de Investigaciones Científicas. Instituto de Química Física; EspañaFil: Volkamer, Rainer. State University of Colorado at Boulder; Estados Unido

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

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 × 106moleculescm-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

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

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.Fil: Koenig, Theodore K.. State University of Colorado at Boulder; Estados Unidos. Cooperative Institute for Research in Environmental Sciences; Estados UnidosFil: Volkamer, Rainer. State University of Colorado at Boulder; Estados Unidos. Cooperative Institute for Research in Environmental Sciences; Estados UnidosFil: Apel, Eric C.. National Center for Atmospheric Research; Estados UnidosFil: Bresch, James F.. National Center for Atmospheric Research; Estados UnidosFil: Cuevas, Carlos A.. Consejo Superior de Investigaciones Científicas. Instituto de Química Física; EspañaFil: Dix, Barbara. State University of Colorado at Boulder; Estados Unidos. Cooperative Institute for Research in Environmental Sciences; Estados UnidosFil: Eloranta, Edwin W.. University of Wisconsin; Estados UnidosFil: Fernandez, Rafael Pedro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Interdisciplinario de Ciencias Básicas. - Universidad Nacional de Cuyo. Instituto Interdisciplinario de Ciencias Básicas; ArgentinaFil: Hall, Samuel R.. National Center for Atmospheric Research; Estados UnidosFil: Hornbrook, Rebecca S.. National Center for Atmospheric Research; Estados UnidosFil: Pierce, R. Bradley. National Environmental Satellite, Data, and Information Service; Estados UnidosFil: Reeves, J. Michael. National Center for Atmospheric Research; Estados UnidosFil: Saiz López, Alfonso. Consejo Superior de Investigaciones Científicas. Instituto de Química Física; EspañaFil: Ullmann, Kirk. National Center for Atmospheric Research; Estados Unido