Regional\nTrends and Spatial Gradients of Total Column\nMethane over India, China, and USAImplications for Emissions\nfrom Coal Mining and Oil/Gas Exploitation

Observation-based\nverification of regional/national methane (CH<sub>4</sub>) emission\ntrends is crucial for transparent monitoring and\nmitigation strategy planning. Although surface observations track\nthe global and sub-hemispheric emission trends well, their sparse\nspatial coverage limits our ability to assess regional trends. Dense\nsatellite observations complement surface observations, offering a\nvaluable means to validate emission trends, especially in regions\nwhere emissions changes are substantial but debated. The uncertainty\nsurrounding the rate of increase in fugitive coal mine emissions in\nChina and emissions from unconventional oil and natural gas (ONG)\nexploration in the United States underscores the need for rigorous\nvalidation. Here, we examine the time evolution of total column dry-air\nmole fractions of CH<sub>4</sub> (XCH<sub>4</sub>) during 2010–2020\nby comparing observations from the GOSAT satellite with simulations\nfrom an atmospheric chemistry-transport model (ACTM). This study analyzes\nemissions and XCH<sub>4</sub> trends in global totals and regions\nof India, China, the USA, and the global tropics. Our results suggest\nthat GAINSv4 emission inventory overestimates the emission increase\nrate for the unconventional ONG sector of USA by about 3 times, while\nEDGARv6 inventory overestimates coal mine emissions in China. Emission\nincreases in China and India agree with those estimated by GAINSv4.\nAnalysis of spatially integrated XCH<sub>4</sub> statistics (mean,\n1-σ standard deviation) reveals a slight systematic underestimation\nof total emissions in China and bias (in both directions) in different\nparts of USA. Our results suggest that long-term satellite observations\nand ACTM simulations can effectively validate emission inventories\nfor CH<sub>4</sub> emissions and emission trends regionally.