Atmos. Chem. Phys. Discuss., 9, 6515-6539, 2009
© Author(s) 2009. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Recent trends in atmospheric methyl bromide: analysis of post-Montreal Protocol variability
S. A. Yvon-Lewis1 and E. S. Saltzman2
1Department of Oceanography, Texas A&M University, College Station, TX 77843, USA
2Department of Earth System Science, University of California Irvine, Irvine, CA, USA

Abstract. The atmospheric methyl bromide (CH3Br) 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 the CH3Br budget, the phaseout schedule, and recent estimates of interannual variability in biomass burning and global OH. In this study, simulations obtained from a time-dependent global model of atmospheric CH3Br emissions and uptake are compared to observations from the NOAA flask network. The model includes an updated global methyl bromide source inventory that includes biofuel combustion emissions estimated at 6.1±3 Gg yr−1 globally. The phaseout of CH3Br 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 trend over the 1997–2005 period. The global budget remains imbalanced, with a large missing source. These results suggest that more than 80% of the missing source does not exhibit significant interannual variability during the phaseout period and, therefore, does not result from underestimating agricultural CH3Br emissions.

Citation: Yvon-Lewis, S. A. and Saltzman, E. S.: Recent trends in atmospheric methyl bromide: analysis of post-Montreal Protocol variability, Atmos. Chem. Phys. Discuss., 9, 6515-6539, doi:10.5194/acpd-9-6515-2009, 2009.
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