Regional Trends and Spatial Gradients of Total Column Methane over India, China, and USA─Implications for Emissions from Coal Mining and Oil/Gas Exploitation.

Observation-based verification of regional/national methane (CH) emission trends is crucial for transparent monitoring and mitigation strategy planning. Although surface observations track the global and sub-hemispheric emission trends well, their sparse spatial coverage limits our ability to assess regional trends. Dense satellite observations complement surface observations, offering a valuable means to validate emission trends, especially in regions where emissions changes are substantial but debated. The uncertainty surrounding the rate of increase in fugitive coal mine emissions in China and emissions from unconventional oil and natural gas (ONG) exploration in the United States underscores the need for rigorous validation. Here, we examine the time evolution of total column dry-air mole fractions of CH (XCH) during 2010-2020 by comparing observations from the GOSAT satellite with simulations from an atmospheric chemistry-transport model (ACTM). This study analyzes emissions and XCH trends in global totals and regions of India, China, the USA, and the global tropics. Our results suggest that GAINSv4 emission inventory overestimates the emission increase rate for the unconventional ONG sector of USA by about 3 times, while EDGARv6 inventory overestimates coal mine emissions in China. Emission increases in China and India agree with those estimated by GAINSv4. Analysis of spatially integrated XCH statistics (mean, 1-σ standard deviation) reveals a slight systematic underestimation of total emissions in China and bias (in both directions) in different parts of USA. Our results suggest that long-term satellite observations and ACTM simulations can effectively validate emission inventories for CH emissions and emission trends regionally.