Abstract
We have collected various kinds of gas samples, which are expected to be source of atmospheric methane. Chemical compositions and δ13C values of the gas samples were measured by using a gas chromatograph and a combined gas chromatograph/combustion/isotope ratio mass spectrometer (GC/C/IRMS ) system, respectively. Analytical precision of δ13C value measurement by using GC/C/IRMS system was examined. Overall error of measurement is between 1 ‰ and 2 ‰, estimated from repeated analysis of running standard gas and δ13C variation with the combustion efficiency. Observed δ13C values of the methane vary singificantly from -65.2‰ to -22.9‰, agrees well with data from literatures. Taking into account a positive correlation between 3He/4He ratios and δ13C values and a recent trend of atmospheric 3He/4He ratio, we discuss contribution of fossil fuel methane to the increase of atmospheric methane.
