Effect of sea salt aerosol on tropospheric bromine chemistry Public Deposited

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  • 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.

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Journal Title
Journal Issue/Number
  • 9
Journal Volume
  • 19
Last Modified
  • 2020-05-27
Resource Type
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  • 1680-7375