Document Type

Article

Publication Date

2016

Publication Title

Atmospheric Chemistry and Physics

ISSN

1680-7324

Volume

16

Issue

18

First Page

12239

Last Page

12271

DOI

http://dx.doi.org/10.5194/acp-16-12239-2016

PubMed ID

27484477

Abstract

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.

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AUTHORS

T. Sherwen (Wolfson Atmospheric Chemistry Laboratories (WACL), Department of Chemistry, University of York, York, YO10 5DD, UK) J. A. Schmidt (Department of Chemistry, University of Copenhagen, Universitetsparken, 2100 Copenhagen O, Denmark) M. J. Evans (Wolfson Atmospheric Chemistry Laboratories (WACL), Department of Chemistry, University of York, York, YO10 5DD, UK) M. J. Evans (National Centre for Atmospheric Science (NCAS), University of York, York, YO10 5DD, UK) L. J. Carpenter (Wolfson Atmospheric Chemistry Laboratories (WACL), Department of Chemistry, University of York, York, YO10 5DD, UK) K. Großmann (Institute of Environmental Physics, University of Heidelberg, Heidelberg, Germany) K. Großmann (now at: Joint Institute For Regional Earth System Science and Engineering (JIFRESSE), University of California Los Angeles, Los Angeles, CA, 90095, USA ) S. D. Eastham (School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA) D. J. Jacob (School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA) B. Dix (Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309-0215, USA) T. K. Koenig (Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309-0215, USA) T. K. Koenig (Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309-021, USA) R. Sinreich (Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309-0215, USA) I. Ortega (Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309-0215, USA) I. Ortega (Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309-021, USA) R. Volkamer (Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309-0215, USA) R. Volkamer (Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309-021, USA) A. Saiz-Lopez (Department of Atmospheric Chemistry and Climate, Institute of Physical Chemistry Rocasolano, CSIC, Madrid, 28006, Spain) C. Prados-Roman (Department of Atmospheric Chemistry and Climate, Institute of Physical Chemistry Rocasolano, CSIC, Madrid, 28006, Spain) C. Prados-Roman (now at: Atmospheric Research and Instrumentation Branch, National Institute for Aerospace Technology (INTA), Madrid, Spain) A. S. Mahajan (Indian Institute of Tropical Meteorology, Maharashtra, 411008, India) C. Ordóñez (Dpto. Física de la Tierra II, Facultad de Ciencias Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain)

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