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GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L20808, doi:10.1029/2006GL027176, 2006

Global lifetime of elemental mercury against oxidation by atomic bromine in the free troposphere

Christopher D. Holmes

Department of Earth and Planetary Sciences and Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA


Daniel J. Jacob

Department of Earth and Planetary Sciences and Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA


Xin Yang

Centre for Atmospheric Science, University of Cambridge, Cambridge, UK


Abstract

We calculate the global mean atmospheric lifetime of elemental mercury (Hg0) against oxidation by atomic bromine (Br) in the troposphere by combining recent kinetic data for the Hg-Br system with modeled global concentrations of tropospheric Br. We obtain a lifetime of 0.5–1.7 years based on the range of kinetic data, implying that oxidation of Hg0 by Br is a major, and possibly dominant, global sink for Hg0. Most of the oxidation takes place in the middle and upper troposphere, where Br concentrations are high and where cold temperatures suppress thermal decomposition of the HgBr intermediate. This oxidation mechanism is consistent with mercury observations, including in particular high gaseous Hg(II) concentrations in Antarctic summer. Better free-tropospheric measurements of bromine radicals and further kinetic study of the Hg-Br system are essential to more accurately assess the global importance of Br as an oxidant of atmospheric Hg0.

Received 9 June 2006; accepted 31 August 2006; published 21 October 2006.

Index Terms: 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0330 Atmospheric Composition and Structure: Geochemical cycles (1030); 0365 Atmospheric Composition and Structure: Troposphere: composition and chemistry; 1065 Geochemistry: Major and trace element geochemistry; 1030 Geochemistry: Geochemical cycles (0330).

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Citation: Holmes, C. D., D. J. Jacob, and X. Yang (2006), Global lifetime of elemental mercury against oxidation by atomic bromine in the free troposphere, Geophys. Res. Lett., 33, L20808, doi:10.1029/2006GL027176.