In collaboration with the National Institute for Environmental Studies, Tohoku University has been investigating the temporal and spatial variations of atmospheric trace species with solar infrared spectroscopy using FTIR at Tsukuba since 1998. We have contributed to the activity of the Detection of Atmospheric Composition Change/InfraRed Working Group (NDACC/IRWG) and collaborated on many species. Now we are trying to retrieve total columns of ¹²CH₃D.
¹²CH₃D is one of the stable isotopes of methane. The isotope ratio depends on its sources and chemical reactions. We can get some information on the history of the species from the isotope ratio. However, it is very difficult to obtain an accurate isotope ratio from infrared spectra. We are trying to analyze ¹²CH₃D because its variability is relatively large. SFIT4 spectral fitting program was used for the retrieval. The absorption lines of ¹²CH₃D exist in 3- and 8- μm regions. As every absorption line of ¹²CH₃D is weak, we used six absorption lines in 3-μm region together to improve the precision of fitting. We also retrieved ¹²CH₃D from seven absorption lines in 8-μm. ¹²CH₄ was retrieved from 3 microwindows (MWs) in 3-μm region using the parameters recommended by NDACC/IRWG.
δD, which is defined as the difference of observed ¹²CH₃D/¹²CH₄ from the standard value, showed the same tendency of the temporal variation in the two independent results (3- and 8- μm). We think the precision is rather good. The temporal variation of the δD showed decrease in recent years. This tendency is consistent with the trend of the surface sampling results.

The Greenhouse gases Observing SATellite (GOSAT) and its successor, GOSAT-2, a series of Japanese satellites collectively known as the GOSAT series, have been observing carbon dioxide (CO₂) and methane (CH₄) since 2009 and 2018, respectively. The third satellite of the series, the Global Observing SATellite for Greenhouse gases and Water cycle (GOSAT-GW), is now being prepared for launch in the first half of Japan's fiscal year 2025. Since 2009, we have provided column-averaged dry-air mole fraction products of CO₂ and CH₄ (XCO₂ and XCH₄, respectively) based on GOSAT and GOSAT-2 observations, validated with data from the Total Carbon Column Observing Network (TCCON), a ground-based observation network of solar-viewing Fourier transform spectrometers. The satellite retrievals of XCO₂ and XCH₄ show increasing trends and clear seasonal cycles, that constitute the longest record of satellite observations of greenhouse gas column averaged dry-air mole fractions. These XCO₂ and XCH₄ have been used to derive whole-atmosphere monthly mean concentrations of CO₂and CH₄, which reflect concentrations in all layers of the atmosphere, to monitor global greenhouse gas levels, and also to estimate global and regional CO₂ and CH₄ fluxes, including Asian region, through atmospheric inversion analyses. These data were submitted to the first Global Stocktake in 2022, a process for assessing the progress toward mitigating global warming since the Paris Agreement. The upcoming GOSAT-GW will be equipped with a grating imaging spectrometer called the Total Anthropogenic and Natural emissions mapping SpectrOmeter-3 (TANSO-3) to monitor greenhouse gases and related spices. New features of the TANSO-3 observations and the latest situation will also be reported.