Simulated Spatial Distribution and Seasonal Variation of Atmospheric Methane over China: Contributions from Key Sources

We used the global atmospheric chemical transport model, GEOS-Chem, to simulate the spatial distribution and seasonal variation of surface-layer methane (CH4) in 2004, and quantify the impacts of individual domestic sources and foreign transport on CH4 concentrations over China. Simulated surface-layer CH4 concentrations over China exhibit maximum concentrations in summer and minimum concentrations in spring. The annual mean CH4 concentrations range from 1800 ppb over western China to 2300 ppb over the more populated eastern China. Foreign emissions were found to have large impacts on CH4 concentrations over China, contributing to about 85% of the CH4 concentrations over western China and about 80% of those over eastern China. The tagged simulation results showed that coal mining, livestock, and waste are the dominant domestic contributors to CH4 concentrations over China, accounting for 36%, 18%, and 16%, respectively, of the annual and national mean increase in CH4 concentration from all domestic emissions. Emissions from rice cultivation were found to make the largest contributions to CH4 concentrations over China in the summer, which is the key factor that leads to the maximum seasonal mean CH4 concentrations in summer.