講演情報
[AAS08-P33]Atmospheric ethane measurements over Asian cities using commercial aircraft: implications for methane emissions
*梅澤 拓1,2、斉藤 拓也1、町田 敏暢1,3、丹羽 洋介1、笹川 基樹1、松枝 秀和4、澤 庸介5、坪井 一寛5,6、石島 健太郎5,6、藤田 遼5 (1.国立環境研究所、2.東北大学、3.広島大学、4.獨協大学、5.気象庁気象研究所、6.気象庁)
キーワード：
エタン、メタン、航空機観測、アジア
CONTRAIL (Comprehensive Observation Network for Trace gases by Airliner) is an ongoing observation program for atmospheric monitoring of greenhouse gases. Air samples have been collected onboard along international flight tracks by using an automatic air sampling equipment or a manual equipment. Some part of the air samples collected from February 2017 to September 2024 (144 flights) was analyzed for ethane (C2H6) in addition to the regularly measured species such as CO2, CH4 and SF6. C2H6 is a useful tracer for CH4 source attribution, for instance by utilizing characteristic natural gas composition ratio of CH4 and C2H6. We present preliminary C2H6 data over 4 Asian cities: Tokyo, Shanghai, Bangkok and Singapore. In the upper troposphere over Tokyo, where the data cover the longest period, C2H6 concentration showed neither increasing nor decreasing trend for 2017–2024. C2H6 increased with decreasing altitude during winter to spring, while almost no vertical gradient was observed in summer. Over Shanghai, magnitude of the C2H6 variability was largest. High C2H6 enhancements up to 6 ppb were observed in the lowermost layer (<4 km altitude) in winter coincident with CH4 enhancement. In such events, the C2H6 to CH4 enhancement ratio reached to 0.02, exceeding those observed over Tokyo and Bangkok. Over Bangkok, vertical gradient in C2H6 was small, but C2H6 and CH4 enhancements were observed near the surface (<2 km) in winter. Elevated CH4 values in the upper troposphere in summer (presumably associated with Asian summer monsoon) were not accompanied by increase in C2H6. Over Singapore, although the data were limited (6 flights), CH4 and C2H6 variabilities were small with almost no vertical gradient. In summary, the measurements showed the largest variabilities in CH4 and C2H6 over Shanghai with the largest C2H6 to CH4 enhancement ratio. This might be explained by higher contribution of emissions associated with natural gas leakage or coal mining in or around the city area.