[A-CG34] Global Carbon Cycle Observation and Analysis

[ACG34-P01] Asian methane outflow captured by the CONTRAIL flask air samplings

*Yosuke Niwa^1,2, Toshinobu Machida¹, Taku Umezawa¹, Kazuhiro Tsuboi², Kentaro Ishijima², Ryo Fujita², Hidekazu Matsueda³, Takuya Saito¹ (1.National Institute for Environmental Studies, 2.Meteorological Research Institute, 3.Dokkyo University)

Keywords:methane, Asia, aircraft, atmospheric transport model

Methane (CH₄) is one of important greenhouse gases. A large part of the global CH₄ emission exists in Asia with various kinds of sources such as fossil fuel exploitation, wetland, rice cultivation and biomass burning. Estimating and monitoring those Asian CH₄ emissions are imperative for better understanding of the growth of the atmospheric CH₄ and for developing a strategy to mitigate CH₄ emissions. Atmospheric observations over the western North Pacific, at the downwind side of Asia, have frequently captured CH₄-rich outflows from the Asian continent. From those elevated CH₄ concentrations, we could obtain useful information of CH₄ emissions in Asia. Especially, sporadic high CH₄ concentrations observed in the upper troposphere during the summer monsoon season are noteworthy because they are largely contributed by biogenic sources that are increased in the summer. Biogenic CH₄ emissions have distinct seasonal variations in response to variations of temperatures and precipitations, and also have a significant role in interannual variations of the atmospheric CH₄. In fact, the commercial aircraft observation project named CONTRAIL has observed notably elevated CH₄ concentrations in the upper troposphere during summer by flask air sampling measurements along Japan-East/Southeast Asia routes. However, the transport mechanism of such a CH₄ outflow is still unclear. Furthermore, the fossil fuel exploitation and other sources that constantly emit CH₄ through a whole year could also contribute the summer CH₄ elevations, which complicates quantitative estimation of the biogenic sources. In this study, the atmospheric transport model NICAM-TM is used to elucidate transport pathways and origins of CH₄ outflows that reach the upper troposphere over the western North Pacific. Furthermore, using simultaneous observations of other chemical species such as ethane (C₂H₆) are used to separate contributions of biogenic sources of CH₄.