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[AAS11-P21] Characteristics of methane in South Asia inferred from enhancement ratios of GHG concentrations based on GOSAT-2
Keywords:GOSAT-2, methane, carbon monoxide, enhancement ratio (ER)
South Asia is one of the largest methane emission regions in the world. We have analyzed XCH4 and XCO data obtained from Thermal And Near infrared Sensor for carbon Observation-Fourier Transform Spectrometer-2 (TANSO-FTS-2) on board Greenhouse gases Observing Satellite-2 (GOSAT-2) over South Asia. We first calculated ΔXCH4 and ΔXCO, which were defined as excess concentrations of XCH4 and XCO relative to their background concentrations, and then calculated Enhancement Ratio (ER) by taking the ratios of ΔXCH4 and ΔXCO. Here, we have divided South Asia into 10 regions: high CH4 emission land areas (three regions), low CH4 emission land areas (five regions), and ocean areas (two regions), and calculated monthly ER values of ΔXCH4/ΔXCO in each of the 10 regions. In this study, we also compared the calculated monthly ER with monthly emission data of CH4 and CO from various emission sources based on EDGAR (Emissions Database for Global Atmospheric Research) database to assess dominant emission sources for each region.
In high CH4 emission land areas, the calculated monthly ER values and their correlation coefficients were higher in September. The corresponding EDGAR emission data showed that CH4 emissions from agricultural sources were high, while agricultural CO emissions were not high in September. This suggests that higher ER in September there could be attributed to agricultural emissions. In the low CH4 emission land areas, especially in southern India, the monthly ER values and their correlation coefficients were higher from September to November. Judging from the EDGAR emission data, agricultural CH4 emissions were very high during this period, which causes the higher ER values, suggesting agricultural origin is a predominant factor to characterize CH4 concentrations there. The timing of high ER values due to agriculture-origin high CH4 in the high CH4 emission land area (northern region) was different from that in the low CH4 emission land area (southern region). This could be attributed to the difference in the timing of the two cropping seasons, the kharif and rabi seasons [Kavitha et al., 2017].
In high CH4 emission land areas, the calculated monthly ER values and their correlation coefficients were higher in September. The corresponding EDGAR emission data showed that CH4 emissions from agricultural sources were high, while agricultural CO emissions were not high in September. This suggests that higher ER in September there could be attributed to agricultural emissions. In the low CH4 emission land areas, especially in southern India, the monthly ER values and their correlation coefficients were higher from September to November. Judging from the EDGAR emission data, agricultural CH4 emissions were very high during this period, which causes the higher ER values, suggesting agricultural origin is a predominant factor to characterize CH4 concentrations there. The timing of high ER values due to agriculture-origin high CH4 in the high CH4 emission land area (northern region) was different from that in the low CH4 emission land area (southern region). This could be attributed to the difference in the timing of the two cropping seasons, the kharif and rabi seasons [Kavitha et al., 2017].