DEVELOPMENT OF A CONTINUOUS MEASUREMENT SYSTEM AND AREAL DISTRIBUTIONOF METHANE IN SOME SOURCE AREAS

For the purpose of investigating the areal distribution of atmospheric methane, we have constructed a continuous measurement system using a flame ionization detector (FID). Since the FID has high sensitivity to almost all hydrocarbons, non-methane hydrocarbons in sample air were reduced by being passed through a heated column filled with Pt catalys t. Through this treatment, non-methane hydrocarbons were effectively r educed, and a low detection limit of 0.004 ppmv and short response tim e of about 10 s were attained. By using this system mounted on a vehic le, the areal distribution of atmospheric methane was measured in two typical source areas: rice paddies and a natural gas field. In the cas e of the gas field, we estimated the emission rate of methane based on the observed profile of methane plumes.