5:15 PM - 7:15 PM
[AAS11-P18] Decrease of the hydrogen isotope ratio of methane observed with FTIR at Tsukuba
Keywords:FTIR, methane, isotope
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.
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.