Recent decline of atmospheric concentration and emission of methane in Nagoya metropolitan area

Anthropogenic emissions of methane (CH4) from major sources such as landfills, automobiles, and rice paddy fields in the Nagoya metropolitan area were estimated using several emission process parameters such as emission factors and activity data for the decade from 1988 to 1997. The sum of CH4 amounts emitted from these three major sources was calculated to be 4.93 Gg of CH4 in 1988 and 5.19 Gg of CH4 in 1997. Methane emissions from the 12 landfill sites located around the Nagoya metropolitan area gradually increased until 1996 and then decreased in 1997, while those from automobiles and rice paddy fields continuously declined for the same decade. The total amount of CH4 emitted from the 12 landfills was much larger than those from other two sources. In 1993, for example, the amount was estimated as 3.26 Gg of CH4,58% of which was generated from the largest landfill site. The excess CH4 concentration in the urban atmosphere, which was estimated from the difference between the CH4 concentration at the urban site and the background CH4 concentration at the Mauna Loa observatory, Hawaii, USA, showed the long-term trends similar to the CH4 emission from the largest landfill site. As a result, we conclude that the CH4 emission from the largest landfill dominantly impacted on the excess CH4 concentration due to the major sources in the Nagoya metropolitan area.