Integrating inventory models and satellite observations for site-level methane emission quantification from MSW...

The waste sector is the third-largest anthropogenic source of methane emissions, significantly contributing to the greenhouse effect. Accurate quantification of landfill methane emissions is essential for effective waste management and emission reduction policies. However, current regional inventory-based assessments often overlook site-specific heterogeneity, while emerging satellite observations remain temporally sparse. This study provides a nationwide, site-level characterization and quantification of methane emissions from MSW landfills in China by integrating bottom-up inventory estimates with hyperspectral satellite observations. We first developed a comprehensive database containing site-specific information for more than 300 major MSW landfills to analyze their spatial and temporal distribution patterns. Methane emissions from individual landfills were then estimated using the IPCC first-order decay method, revealing an increase from 1.015 Mt in 2005 to a peak of 2.161 Mt around 2015, followed by a decline to 1.98 Mt in 2023. We further compared these inventory results with hyperspectral satellite observations (EMIT, PRISMA) for three typical landfill sites. The comparison revealed that satellite-detected instantaneous emissions consistently exceed inventory-based averages, quantifying a systematic bias in current IPCC models which tend to underestimate fugitive leaks. Uncertainty in the results primarily arises from parameter assumptions in inventory models and wind-related variability in satellite-based flux inversion. Finally, a scenario analysis projects that the full implementation of China's "Zero Waste" policy could reduce landfill methane emissions by approximately 59 % by 2030. Our findings highlight the importance of combining bottom-up inventories with top-down satellite monitoring for improved landfill management and provide valuable insights for national carbon mitigation strategies.