The distribution and trends in Chinese methane emissions, 2010-2017

We use satellite observations of methane (CH₄) from the Japanese Greenhouse gases Observing SATellite (GOSAT) to study the temporal and spatial changes in Chinese CH₄ emissions from 2010 to 2017. We use v12.5.0 of the GEOS-Chem model of atmospheric chemistry and transport, driven by prior emission inventories, to describe observed variations of atmospheric CH₄. To infer fluxes from North, central, South, East, northeast, northwest and southwest China we use an established ensemble Kalman filter method in conjunction with the GEOS-Chem model. We find that annual nationwide CH₄ emissions decreased from 53 Tg in 2010 to 49 Tg in 2012, but then increased to 54 Tg in 2017. Emissions from eastern China represent the largest regional contribution to the nationwide total, accounting for 22%, while southern and northeast China each represent the smallest regional contributions of 7%. We find that emission trends of various regions are very different. Generally, regional CH₄ emissions are smallest during January and peak in July. We report a downward trend during Spring over southwest and southern regions but find no significant trend in northern and northwest China.  By analyzing the seasonal maximum and minimum values over each region, we find that annual mean trends are driven by changes in seasonal peak values, with no obvious trend in the seasonal minimum. We will discuss how changes in coal mine emissions may have impacted nationwide trends after 2013.