ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-9-5963-2009 Recent trends in atmospheric methyl bromide: analysis of post-Montreal Protocol variability Yvon-Lewis S. A. 1 Saltzman E. S. 2 Montzka S. A. 3 Department of Oceanography, Texas A & M University, College Station, TX 77843, USA Department of Earth System Science, University of California Irvine, Irvine, CA 92697, USA Global Monitoring Division, NOAA/ESRL, Boulder, CO 80305, USA 19 08 2009 9 16 5963 5974 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/9/5963/2009/acp-9-5963-2009.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/9/5963/2009/acp-9-5963-2009.pdf

The atmospheric methyl bromide (CH<sub>3</sub>Br) burden has declined in recent years, in response to the phaseout of agricultural and structural fumigation consumption under the amendments to the Montreal Protocol. The timing and magnitude of this decrease represents an opportunity to examine our current understanding of atmospheric CH<sub>3</sub>Br and its budget, response to the phaseout, and response to interannual variability in biomass burning and global OH. In this study, simulations obtained from a time-dependent global model of atmospheric CH<sub>3</sub>Br emissions and uptake are compared to observations from the NOAA flask network. The model includes a detailed gridded ocean model coupled to a time-dependant atmospheric 2-box model. The phaseout of CH<sub>3</sub>Br production for agricultural uses began in 1998, concurrent with the pulse in biomass burning associated with the 1998 El Niño. The combined effects of three factors (biomass burning, global OH, and anthropogenic phaseout) appear to explain most of the observed atmospheric methyl bromide variability over the 1997–2008 period. The global budget remains imbalanced, with a large missing source indicated. The missing source does not exhibit a systematic decline during the phaseout period, and therefore, is not the result of significantly underestimating non-QPS agricultural CH<sub>3</sub>Br emissions. The model results suggest that the oceans should be less undersaturated than before the phaseout began.

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