Article open access publication

Modeling the observed tropospheric BrO background: Importance of multiphase chemistry and implications for ozone, OH, and mercury

Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), ISSN 2169-8996

Volume 121, 19, 2016

DOI:10.1002/2015jd024229, Dimensions: pub.1025614661,

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  1. (1) University of Copenhagen, grid.5254.6, KU
  2. (2) Harvard University, grid.38142.3c
  3. (3) Wolfson Atmospheric Chemistry Laboratories (WACL), Department of Chemistry University of York York UK
  4. (4) Goddard Space Flight Center, grid.133275.1
  5. (5) Harvard-Smithsonian Center for Astrophysics, grid.455754.2
  6. (6) Centre for Oceanography and Atmospheric Science, National Centre for Atmospheric Science University of East Anglia Norwich UK
  7. (7) Centre for Atmospheric Science, School of Earth, Atmospheric and Environmental Sciences University of Manchester Manchester UK
  8. (8) University of Michigan, grid.214458.e
  9. (9) University of Colorado Boulder, grid.266190.a
  10. (10) Cooperative Institute for Research in Environmental Sciences, grid.464551.7

Description

Aircraft and satellite observations indicate the presence of ppt (ppt ≡ pmol/mol) levels of BrO in the free troposphere with important implications for the tropospheric budgets of ozone, OH, and mercury. We can reproduce these observations with the GEOS-Chem global tropospheric chemistry model by including a broader consideration of multiphase halogen (Br-Cl) chemistry than has been done in the past. Important reactions for regenerating BrO from its nonradical reservoirs include HOBr + Br−/Cl− in both aerosols and clouds, and oxidation of Br− by ClNO3 and ozone. Most tropospheric BrO in the model is in the free troposphere, consistent with observations and originates mainly from the photolysis and oxidation of ocean-emitted CHBr3. Stratospheric input is also important in the upper troposphere. Including production of gas phase inorganic bromine from debromination of acidified sea salt aerosol increases free tropospheric Bry by about 30%. We find HOBr to be the dominant gas-phase reservoir of inorganic bromine. Halogen (Br-Cl) radical chemistry as implemented here in GEOS-Chem drives 14% and 11% decreases in the global burdens of tropospheric ozone and OH, respectively, a 16% increase in the atmospheric lifetime of methane, and an atmospheric lifetime of 6 months for elemental mercury. The dominant mechanism for the Br-Cl driven tropospheric ozone decrease is oxidation of NOx by formation and hydrolysis of BrNO3 and ClNO3.

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Times Cited: 61

Field Citation Ratio (FCR): 10.2

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Green, Accepted