Long-Term Trends of Atmospheric CH4 Concentration across China from 2002 to 2016

Spatiotemporal variations of atmospheric CH4 from 2002 to 2016 across China were detected, based on the Atmospheric Infrared Sounder (AIRS) sixth-layer CH4 concentration. The CH4 concentration showed good consistency with the ground measurements of surface CH4 concentration from the World Data Centre for Greenhouse Gases (WDCGG) (R2 = 0.83, p < 0.01), indicating that the remotely-sensed CH4 reflected the spatial and temporal variations of surface CH4 concentration. Across China, three hotspots of CH4 concentration were found in northern Xinjiang, the northeast of Inner Mongolia/Heilongjiang, and the Norgay plateau in northwest Sichuan. The CH4 concentration showed obviously seasonal variations, with the maximum CH4 concentration occurring in summer, followed by the autumn, winter, and spring. Furthermore, the CH4 concentration showed significantly increasing trends across China, with the rate of increase ranging from ~0.29 to 0.62 ppb·month−1, which would bring a 0.0019~0.014 mK potential rise in surface temperature response over China. In particular, the most rapidly increasing rates occurred in the Qinghai-Tibet plateau, while relatively low rates occurred in southeast China.