[A-AS09] Atmospheric Chemistry

[AAS09-P06] Temporal variation of the isotope ratio of methane observed with FTIR at Tsukuba

*Isao Murata¹, Tomoo Nagahama², Isamu Morino³, Hideaki Nakajima³ (1.Graduate School of Environmental Studies, Tohoku University, 2.Institute for Space-Earth Environmental Research, Nagoya University, 3.National Institute for Environmental Studies)

Keywords:FTIR, methane, isotope

We are trying to retrieve total columns (and vertical profiles) of methane isotopes (¹²CH₄ and ¹²CH₃D) from the spectra observed with solar infrared spectroscopy using a Fourier transform spectrometer (FTIR) at Tsukuba. SFIT4 spectral fitting program was used for the retrieval.
¹²CH₄ was retrieved from 3 microwindows (MWs) in 3 µm region using the parameters recommended by the Network for the Detection of Atmospheric Composition Change/InfraRed Working Group (NDACC/IRWG). The absorption lines of ¹²CH₃D are also exist in 3 and 8 µm regions. We retrieved ¹²CH₃D total columns from 4 MWs in 3 µm region for 2014 and 2023 and got the results with fairly small random error. δD of total column was calculated using ¹²CH₄ total column observed on the same day and the results in 2023 were lower than those in 2014. This tendency is consistent with the trend of the surface sampling results.