Global Inorganic Source of Atmospheric Bromine

S. Enami, C. D. Vecitis, J. Cheng, M. R. Hoffmann, and A. J. Colussi*
W. M. Keck Laboratories, California Institute of Technology, Pasadena, California 91125
J. Phys. Chem. A, 2007, 111 (36), pp 8749–8752
DOI: 10.1021/jp074903r
Publication Date (Web): August 22, 2007
Copyright © 2007 American Chemical Society

Abstract

Abstract Image

A few bromine molecules per trillion (ppt) causes the complete destruction of ozone in the lower troposphere during polar spring and about half of the losses associated with the “ozone hole” in the stratosphere. Recent field and aerial measurements of the proxy BrO in the free troposphere suggest an even more pervasive global role for bromine. Models, which quantify ozone trends by assuming atmospheric inorganic bromine (Bry) stems exclusively from long-lived bromoalkane gases, significantly underpredict BrO measurements. This discrepancy effectively implies a ubiquitous tropospheric background level of 4 ppt Bry of unknown origin. Here, we report that I- efficiently catalyzes the oxidation of Br- and Cl- in aqueous nanodroplets exposed to ozone, the everpresent atmospheric oxidizer, under conditions resembling those encountered in marine aerosols. Br- and Cl-, which are rather unreactive toward O3 and were previously deemed unlikely direct precursors of atmospheric halogens, are readily converted into IBr2- and ICl2- en route to Br2(g) and Cl2(g) in the presence of I-. Fine sea salt aerosol particles, which are predictably and demonstrably enriched in I- and Br-, are thus expected to globally release photoactive halogen compounds into the atmosphere, even in the absence of sunlight.

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History

  • Published In Issue September 13, 2007
  • Received June 22, 2007
    Revised July 20, 2007

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