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From the same journal

Tropospheric bromine chemistry: implications for present and pre-industrial ozone and mercury

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Author(s)

  • J. P. Parrella
  • D. J. Jacob
  • Q. Liang
  • Y. Zhang
  • L. J. Mickley
  • B. Miller
  • M. J. Evans
  • X. Yang
  • J. A. Pyle
  • N. Theys
  • M. Van Roozendael

Department/unit(s)

Publication details

JournalAtmospheric Chemistry and Physics
DatePublished - 2012
Issue number15
Volume12
Number of pages18
Pages (from-to)6723-6740
Original languageEnglish

Abstract

We present a new model for the global tropospheric chemistry of inorganic bromine (Br-y) 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.

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