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Discussion papers
https://doi.org/10.5194/acp-2018-1239
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2018-1239
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 30 Nov 2018

Research article | 30 Nov 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Effect of sea-salt aerosol on tropospheric bromine chemistry

Lei Zhu1, Daniel J. Jacob1,2, Sebastian D. Eastham3, Melissa P. Sulprizio1, Xuan Wang1, Tomás Sherwen4,5, Mat J. Evans4,5, Qianjie Chen6,a, Becky Alexander6, Theodore K. Koenig7,8, Rainer Volkamer7,8, L. Gregory Huey9, Michael Le Breton10,11, Thomas J. Bannan10, and Carl J. Percival10,b Lei Zhu et al.
  • 1John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
  • 2Department of Earth and Planetary Sciences, Harvard Univ ersity, Cambridge, MA, USA
  • 3Laboratory for Aviation and the Environment, Massachusetts Institute of Technology, Cambridge, MA, USA
  • 4Wolfson Atmospheric Chemistry Laboratories, Department of Chemistry, University of York, York, UK
  • 5National Centre for Atmos pheric Science (NCAS), University of York, York, UK
  • 6Department of Atmospheric Sciences, University of Washington, Seattle, WA, USA
  • 7Department of Chemistry, University of Colorado, Boulder, CO, USA
  • 8Cooperative Institute for Research in Environmental Scie nces (CIRES), Boulder, CO, USA
  • 9School of Earth & Atmospheric Sciences, Georgia Tech, Atlanta, Georgia, USA
  • 10The Centre for Atmospheric Science, School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Simon Building, Brunswick Street, Manchester, M13 9PL, UK
  • 11Department of Chemistry and Molecular Biology, University of Gothenburg , Medicinaregatan 9 C, 40530, Gothenburg, Sweden
  • anow at: Department of Chemistry, University of Michigan, Ann Arbor, MI, USA
  • bnow at: Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA, USA

Abstract. Bromine radicals influence global tropospheric chemistry by depleting ozone and OH, and by oxidizing elemental mercury, sulfur species, and volatile organic compounds. Observations typically indicate a 50% depletion of sea salt aerosol (SSA) bromide relative to seawater composition, implying that SSA debromination could be the dominant global source of tropospheric bromine. However, it has been difficult to reconcile this large source with the relatively low BrO concentrations observed in the marine boundary layer (MBL). Here we present a new mechanistic description of SSA debromination in the GEOS-Chem global atmospheric chemistry model with a detailed representation of halogen (Cl, Br, and I) chemistry. We show, for the first time, observed levels of SSA debromination can be reproduced in a manner consistent with observed BrO concentrations. Bromine radical sinks from the HOBr + S(IV) heterogeneous reactions and from ocean emission of acetaldehyde are found to be critical in moderating tropospheric BrO levels. The resulting HBr is rapidly taken up by SSA and also deposited. We find that the source of bromine radicals is mostly from SSA in the MBL, but from organobromines in the free troposphere. Simulated BrO in the MBL is generally much higher in winter than in summer due to a combination of greater SSA emission and weaker radiation. Outstanding issues are the model underestimate of free tropospheric BrO, driven by the HOBr + S(IV) reactions, and uncertainty regarding HBr uptake by SSA.

Lei Zhu et al.
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GEOS-Chem 12.0.0 The International GEOS-Chem User Community https://doi.org/10.5281/zenodo.1343547

Lei Zhu et al.
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Short summary
We quantify the effect of sea-salt aerosol on tropospheric bromine chemistry with a new mechanistic description of the halogen chemistry in a global atmospheric chemistry model. For the first time, we are able to reproduce the observed levels of bromide activation from the sea-salt aerosol in a manner consistent with bromine oxide radical measured from various platforms. Sea-salt aerosol plays a far more complex role in global tropospheric chemistry than previously recognized.
We quantify the effect of sea-salt aerosol on tropospheric bromine chemistry with a new...
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