ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-9-27693-2009 Optimal estimation of the surface fluxes of methyl chloride using a 3-D global chemical transport model Xiao X. 1 12 Prinn R. G. 1 Fraser P. J. 2 Simmonds P. G. 3 Weiss R. F. 4 O'Doherty S. 3 Miller B. R. 4 Salameh P. K. 4 Harth C. M. 4 Krummel P. B. 2 Porter L. W. 5 13 Mühle J. 4 Greally B. R. 3 Cunnold D. 6 13 Wang R. 6 Montzka S. A. 7 Elkins J. W. 7 Dutton G. S. 7 Thompson T. M. 7 Butler J. H. 7 Hall B. D. 7 Reimann S. 8 Vollmer M. K. 8 Stordal F. 9 Lunder C. 9 Maione M. 10 Arduini J. 10 Yokouchi Y. 11 Department of Earth, Atmospheric, and Planetary Sciences, MIT, Cambridge, MA 02139, USA Center for Australian Weather and Climate Research, CSIRO Marine and Atmospheric Research, Aspendale, Victoria, 3195, Australia School of Chemistry, University of Bristol, Bristol, UK Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093, USA Center for Australian Weather and Climate Research, Bureau of Meteorology, Melbourne, Victoria, 3000, Australia Georgia Institute of Technology, Atlanta, GA, USA ESRL, NOAA, Boulder, CO, USA Swiss Federal Institute for Materials Science and Technology, Laboratory for Air Pollution/Environmental Technology, Duebendorf, Switzerland Norwegian Institute for Air Research, Kjeller, Norway University of Urbino, Urbino, 61029, Italy National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan now at: Civil & Environmental Engineering, Rice University, Houston, TX, USA Deceased 23 12 2009 9 6 27693 27744 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-discuss.net/9/27693/2009/acpd-9-27693-2009.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/9/27693/2009/acpd-9-27693-2009.pdf

Methyl chloride (CH<sub>3</sub>Cl) is a chlorine-containing trace gas in the atmosphere contributing significantly to stratospheric ozone depletion. Large uncertainties in estimates of its source and sink magnitudes and temporal and spatial variations currently exist. GEIA inventories and other bottom-up emission estimates are used to construct a priori maps of the surface fluxes of CH<sub>3</sub>Cl. The Model of Atmospheric Transport and Chemistry (MATCH), driven by NCEP interannually varying meteorological data, is then used to simulate CH<sub>3</sub>Cl mole fractions and quantify the time series of sensitivities of the mole fractions at each measurement site to the surface fluxes of various regional and global sources and sinks. We then implement the Kalman filter (with the unit pulse response method) to estimate the surface fluxes on regional/global scales with monthly resolution from January 2000 to December 2004. High frequency observations from the AGAGE, SOGE, NIES, and NOAA/ESRL HATS in situ networks and low frequency observations from the NOAA/ESRL HATS flask network are used to constrain the source and sink magnitudes. The inversion results indicate global total emissions around 4100&plusmn;470 Gg yr<sup>&minus;1</sup> with very large emissions of 2200&plusmn;390 Gg yr<sup>&minus;1</sup> from tropical plants, which turn out to be the largest single source in the CH<sub>3</sub>Cl budget. Relative to their a priori annual estimates, the inversion increases global annual fungal and tropical emissions, and reduces the global oceanic source. The inversion implies greater seasonal and interannual oscillations of the natural sources and sink of CH<sub>3</sub>Cl compared to the a priori. The inversion also reflects the strong effects of the 2002/2003 globally widespread heat waves and droughts on global emissions from tropical plants, biomass burning and salt marshes, and on the soil sink.

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