Application of satellite observations to verify methane emission inventories
Methane is a strong greenhouse gas and is responsible for roughly a quarter of radiative forcing since industrialization.Reducing anthropogenic methane emissions is considered a vital measure to slow down climate change.Conventional"bottom-up"inventories,which are compiled based on emission factors and activity data,are subject to large uncertainties.Atmospheric observations such as those made by satellite instruments provide a useful"top-down"approach for verifying and improving emission inventories.This study aims to present the application of satellite observations to the verification of methane emission inventories through forward simulations and inversion analyses.We first presented varied types of satellite observations(short-wave infrared vs.thermal infrared observations,area-flux mappers vs.point-source imagers)and retrieval methods(CO2-proxy method vs.full-physics method)and their suitability for inventory verification.We then extensively discussed the role of chemical transport models in interpreting satellite observations,the method of properly comparing model methane simulations to satellite column observations,and the effects of simulation errors on emission inventory verification.Finally,we demonstrated the two-stage verification with forward simulations and then an inverse analysis for global methane emissions.They were conducted using the GEOS-Chem chemical transport model,GOSAT methane column observations for 2020,and two sets of bottom-up emission inventories.In the forward simulation,we developed a bias correction procedure to reduce the season-and latitude-dependent systematic biases.The bias-corrected simulation results were compared with satellite column observations to qualitatively assess the quality of emission inventories.In the inverse analyses,we presented the quantification of emissions for top methane-emitting countries.Results showed that the prior inventory significantly overestimated methane emissions in China and Indonesia,underestimated those in Russia,India,and Bangladesh,and statistically agreed with the rest.Finally,an outlook for the application of satellite observations in the field of methane monitoring was provided,and the direction for future technical developments was discussed.This study demonstrated the potential of using satellite observations to verify methane emission inventories.While the forward simulation is a fast but qualitative method,the inverse analyses provide a more quantitative verification of emission inventories.
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