Spatial and Temporal Variations of Lower Tropospheric Methane During 2010–2011 in China

Estimates of methane (CH₄) concentrations in the lower troposphere over the land surfaces of the world, and in more detail for China, were derived from data from the Atmospheric Infrared Sounder (AIRS). Derivation of CH₄ estimates is described, and these were validated with reference to CH₄ concentrations analyzed for air samples in three regions of China and the observations from three global baseline sites. The values of sample points and three global baseline sites were extracted from remotely sensed images. The correlation coefficients between remotely sensed geographical point estimates of CH₄ and observations were equal to 0.779 and 0.763. Seasonal and monthly variation of CH₄ concentrations for the 2010-2011 year and the spatial variation of these concentrations for the troposphere over China derived from remotely sensed data were mapped and interpreted with reference to possible sources of CH₄ emission. Methane concentrations were about 15 ppb higher in winter than summer. The changes in concentrations were about 50 ppb in Inner Mongolian Plateau between September and October 2010, northwest China between February and March 2011. Variations of CH₄ concentration are considered with reference to mixing of atmospheric gases by oceanic influences and to sources of CH₄ emissions including vegetation cover particularly wetland, crop, and pastoral land use.