Trends of atmospheric methane in Beijing

The concentration of atmospheric methane in Beijing is still increasing, although its annual trend has significantly decreased from 2.0% yr⁻¹ in 1985–1989 to 0.5% yr⁻¹ in 1990–1997. The seasonal variability of methane concentration apparently appeared in a double-peak pattern with one peak in winter and the other in summer. It is known that the seasonal inter-annual variations of atmospheric methane in Beijing are different from year to year. From 1986 to 1997, the concentrations of atmospheric methane increased by 184 ppbv, in which about 37% was due to its increase in winter and 21% in summer. After 1993, the trends of methane concentration in summer, which are mainly due to emission from biogenic sources, are negative, while their trends in winter, which are mainly due to emission from non-biogenic sources, are positive with a value of about 25 ppbv yr⁻¹. As a result, the seasonal inter-annual trends from 1993 to 1997 were mainly due to the increase of methane emission from non-biogenic sources in winter. It implies, therefore, that in Beijing the biogenic sources have been decreasing but the non-biogenic ones, such as fossil fuel combustion, have increased.