Tropospheric Bromine Chemistry: Implications for Present and Pre-Industrial Ozone and Mercury

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Tropospheric Bromine Chemistry: Implications for Present and Pre-Industrial Ozone and Mercury

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Title: Tropospheric Bromine Chemistry: Implications for Present and Pre-Industrial Ozone and Mercury
Author: Parrella, J. P.; Jacob, Daniel J.; Liang, Q.; Zhang, Y.; Mickley, Loretta J.; Miller, Benjamin Franklin; Evans, M. J.; Yang, X.; Pyle, J. A.; Theys, N.; Van Roozendael, M.

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Citation: Parrella, J. P., D. J. Jacob, Q. Liang, Y. Zhang, L. J. Mickley, B. Miller, M. J. Evans, et al. 2012. Tropospheric Bromine Chemistry: Implications for Present and Pre-Industrial Ozone and Mercury. Atmospheric Chemistry and Physics 12, no. 15: 6723–6740.
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Abstract: We present a new model for the global tropospheric chemistry of inorganic bromine (Bry) coupled to oxidant-aerosol chemistry in the GEOS-Chem chemical transport model (CTM). Sources of tropospheric Bry include debromination of sea-salt aerosol, photolysis and oxidation of short-lived bromocarbons, and transport from the stratosphere. Comparison to a GOME-2 satellite climatology of tropospheric BrO columns shows that the model can reproduce the observed increase of BrO with latitude, the northern mid-latitudes maximum in winter, and the Arctic maximum in spring. This successful simulation is contingent on the HOBr + HBr reaction taking place in aqueous aerosols and ice clouds. Bromine chemistry in the model decreases tropospheric ozone mixing ratios by <1–8 nmol mol−1 (6.5% globally), with the largest effects in the northern extratropics in spring. The global mean tropospheric OH concentration decreases by 4%. Inclusion of bromine chemistry improves the ability of global models (GEOS-Chem and p-TOMCAT) to simulate observed 19th-century ozone and its seasonality. Bromine effects on tropospheric ozone are comparable in the present-day and pre-industrial atmospheres so that estimates of anthropogenic radiative forcing are minimally affected. Br atom concentrations are 40% higher in the pre-industrial atmosphere due to lower ozone, which would decrease by a factor of 2 the atmospheric lifetime of elemental mercury against oxidation by Br. This suggests that historical anthropogenic mercury emissions may have mostly deposited to northern mid-latitudes, enriching the corresponding surface reservoirs. The persistent rise in background surface ozone at northern mid-latitudes during the past decades could possibly contribute to the observations of elevated mercury in subsurface waters of the North Atlantic.
Published Version: doi:10.5194/acp-12-6723-2012
Terms of Use: This article is made available under the terms and conditions applicable to Other Posted Material, as set forth at http://nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of-use#LAA
Citable link to this page: http://nrs.harvard.edu/urn-3:HUL.InstRepos:11916599
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