CONTINUOUS MONITORING OF THE METHANE CONCENTRATION IN THE URBAN ATMOSPHERE OF NAGOYA, 1990-1993

Continuous monitoring of the atmospheric concentration of methane (CH4 ) has been carried out since August, 1990, in Nagoya, which is one of the typical urban areas of Japan. The atmospheric CH4 concentration in Nagoya has shown some characteristic seasonal oscillations and daily changes; the CH4 concentration was generally lower in the summer and h igher in the winter; it was also relatively lower during the day and h igher during the night. The annual mean concentration was 1.94 ppmv in 1991, 1.93 ppmv in 1992 and 1.98 ppmv in 1993. These values are highe r than the global average (1.72 ppmv) reported by IPCC (1990), or the average in the northern hemisphere. The annual rate of increase for th e last three years (from January, 1991, to December, 1993) was 2.78X10 (-2) ppmv/year, which corresponds to 1.4%/year. This rate of increase is also larger than that given in the IPCC report (0.9%) in 1990. Thes e results suggest that there are some possible emission sources of CH4 in the urban area of Nagoya. Furthermore, structural changes of the u rban atmosphere should be taken into consideration when explaining the daily changes as well as the seasonal oscillation of methane.