ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-4-3419-2004 Mass balance inverse modelling of methane in the 1990s using a Chemistry Transport Model Butler T. M. 1 3 Simmonds I. 1 Rayner P. J. 2 School of Earth Sciences, Melbourne University, Australia CSIRO Atmospheric Research, Melbourne, Australia Present affiliation: Max Planck Institute for Chemistry, Mainz, Germany 22 06 2004 4 3 3419 3483 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/4/3419/2004/acpd-4-3419-2004.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/4/3419/2004/acpd-4-3419-2004.pdf

A mass balance inverse modelling procedure is applied with a time-dependent methane concentration boundary condition and a chemical transport model to relate observed changes in the surface distribution of methane mixing ratios during the 1990s to changes in its surface sources. This work serves as an important starting point for future inverse modelling work examining changes in both the source and sink terms in the methane budget together. The model reproduces essential features of the global methane cycle, such as the latitudinal distribution and seasonal cycle of fluxes, without using a priori knowledge of methane fluxes. A detailed description of the temporal and spatial variability of the fluxes diagnosed by the inverse procedure is presented, and compared with previously hypothesised changes in the methane budget, and previous inverse modelling studies. The sensitivity of the inverse results to the forcing data supplied by surface measurements of methane from the NOAA CMDL cooperative air sampling network is also examined.