Study of atmospheric CH4 mole fractions at three WMO/GAW stations in China

Atmospheric CH4 mole fractions were continuously measured from 2009 to 2011 at three WMO/GAW stations in China (Lin'an, LAN; Longfengshan, LFS; and Waliguan, WLG) using three Cavity Ring Down Spectroscopy instruments. LAN and LFS are GAW regional measurement stations. LAN is located in China's most economically developed region, and LFS is in a rice production area (planting area>40,000 km(2)). WLG is a global measurement station in remote northwest China. At LAN, high methane mole fractions are observed in all seasons. Surface winds from the northeast enhance CH4 values, with a maximum increase of 3215 ppb in summer. The peak to peak amplitude of the seasonal cycle is 7735 ppb. At LFS, the diurnal cycle amplitude is approximately constant throughout the year except summer, when a value of 19665 ppb is observed. CH4 values at LFS reach their peak in July, which is different from seasonal variations typically observed in the northern hemisphere. CH4 mole fractions at WLG show both the smallest values and the lowest variability. Maximum values occur during summer, which is different from other northern hemisphere WMO/GAW global stations. The seasonal cycle amplitude is 1711 ppb. The linear growth rates at LAN, LFS, and WLG are 8.0 +/- 1.2, 7.9 +/- 0.9, and 9.4 +/- 0.2 ppb yr(-1), respectively, which are all larger than the global mean over the same 3year period. Results from this study attempt to improve our basic understanding of observed atmospheric CH4 in China.