National Institute for Environmental Studies
National Institute for Environmental Studies
National Institute for Environmental Studies
2020 Volume 98 Issue 1 Pages 115-127
Although methane plays an important role in climate change and atmospheric chemistry, its global budget remains quantitatively uncertain mainly because of a wide variety of source types. The stable carbon isotope ratio of atmospheric methane (δ13C-CH4) is useful for separating contributions of different source categories, but owing to the complex and laborious analysis, limited measurement data exist. We present a new system for δ13C-CH4 measurement, optimized for the automated analysis of air samples. Although the system is designed, in principle, similarly to those in previous studies, we successfully set up the system with no use of cryogens (e.g., liquid nitrogen) and attained reproducibility sufficient to analyze atmospheric variations (∼0.1 ‰). We performed automated continuous measurements of ambient air outside our laboratory at about hourly intervals for 2 months, which characterized imprint of local methane sources well. Future measurement operation for flask air samples from existing atmospheric monitoring programs will provide a large number of atmospheric δ13C-CH4 data.