[A-AS09] 大気化学

[AAS09-P05] New measurements of stable carbon isotope signatures of methane sources in Asia

*梅澤 拓¹、寺尾 有希夫¹、石垣 智基¹、蛯江 美孝¹、亀山 哲¹、伊藤 昭彦^2,1、Noppharit Sutthasil^3,1、Komsilp Wangyao^4,1、Panida Payomthip^1,4、Wilasinee Yoochatchaval⁵、Shohei Nomura¹、Md. Kawser Ahmed⁶、Seema Rani⁷ (1.国立研究開発法人国立環境研究所、2.東京大学、3.Mae Fah Luang University、4.King Mongkut’s University of Technology Thonburi、5.Kasetsart University、6.Dhaka University、7.Bangladesh Oceanographic Research Institute)

キーワード：メタン、同位体、アジア、埋立地、排水、水田

Methane (CH₄) is a strong greenhouse gas emitted from both natural and anthropogenic sources. To effectively take emission reduction actions, accurate information on locations and magnitudes of individual CH₄ sources is needed. Stable carbon isotope ratio (δ¹³C) of CH₄ indicates production and oxidation processes of CH₄ and thus useful for constraining process models of CH₄ emissions. Since δ¹³C varies depending on types of CH₄ sources, it also contributes to separately estimating emission magnitudes of different CH₄ sources. However, measurements of δ¹³C signatures of CH₄ sources in Asia are very limited, hampering application studies for the Asian region. In this study, we conducted measurements of δ¹³C of CH₄ for air samples collected from various CH₄ sources in Asia (Japan, Thailand and Bangladesh). In Japan, we collected CH₄ emitted from known sources including decentralized wastewater treatment tanks, a landfill site, and rice paddy. In Thailand, CH₄ samples were collected from a landfill site, a wastewater treatment plant, and a wastewater manhole. In Bangladesh, we collected sample air at rice paddy, a CNG station, and an agricultural burning site. Average δ¹³C signatures of CH₄ from the landfill sites were estimated from ambient air with values from -58 to -52‰; those values agreed between landfill sites in Japan and Thailand. At both sites, measurements from underground pipes and the surface soil layer showed larger variations, plausibly reflecting varying degree of CH₄ oxidation in aerobic layers. δ¹³C of CH₄ from wastewater treatment in Japan and Thailand varied more largely from -60 to -38‰. Rice paddies in Japan and Bangladesh emitted CH₄ with δ¹³C values from -68 to -60‰. Compressed natural gas (CNG) in Bangladesh showed a δ¹³C value of -41‰. These values for the various sources are in general agreement to those previously reported for same types of sources for regions outside Asia. Agricultural burning in Bangladesh showed a value of -35‰, which is significantly lower than those reported for other regions. The δ¹³C signatures for the CH₄ sources in Asia obtained in this study significantly fill the current data gap and help upcoming application studies.