Decadal trends of atmospheric methane in East Asia from 1991 to 2013

Abstract

Discrete air sample measurements of atmospheric methane (CH4) were analyzed at the following East Asian monitoring sites: Mt. Waliguan (WLG), China; Ulaan Uul (UUM), Mongolia; Tae-ahn Peninsula (TAP), Korea; and the remote high-altitude site, Mauna Loa (MLO), Hawaii, for 1991∼2013. The changes of CH4 emission from regional sources resulted in a trend in the difference between the East Asian monitoring sites and MLO. The average annual growth rate in the difference between TAP and MLO has a larger 1σ uncertainty of the trend of 0.3 ppb year−1 compared with WLG and UUM. TAP is influenced by changes in regional sources. Therefore, the annual increase varies greatly from year to year. The East Asian monitoring sites show a different seasonal cycle. The average seasonal variation at TAP has higher standard deviation in July and August. During July and August, there is inflow of air depleted in CH4 by OH radical over the North Pacific Ocean as well as very high CH4 from paddy field in eastern China. The average annual growth rate in the difference between TAP and MLO was increasing with 1.4 ± 1.2 ppb year−1 for the regional polluted continental (RPC) air mass originating from China.