The Atmospheric Methane Concentration in Japan between 1980 and 1989

Abstract

In order to analyze the trends and seasonal cycles of atmospheric methane concentration in Japan, the data of monthly averages of methane concentration between April 1980 and March 1990 at the 23 monitoring stations, which were installed by Japan Environment Agency, were used.
The overall monthly average of methane concentration had increased by 0.011±0.006 (1δ) ppmv/v per year, and the average methane concentration in March 1990 was 1.821±0.046 ppmv/v. All data show the seasonal cycle of methane concentration, which has a maximum value in December and a minimum in August.
The relationship between the initial concentration of mathane in the first month of a year, namely the methane concentrations in April, and each yearly increase of methane concentration shows that the yearly increase of methane concentartion became smaller as the initial methane concentration became larger. Therefore, it seems that the methane concentration in Japan tends to become uniform. From the results of principal factor analysis of monthly averages at the 21 monitoring stations over 10 years, it was obtained that two factors had affected the seasonal cycles of methane concentration. The first factor represents the character that methane concentration becomes lower in summer and higher in winter, and the second factor shows the character that methane concentration becomes higher in summer and lower in winter.