Evaluation of methane emission from MSW landfills in China, India, and the US from space using a two-tier approach

Methane emissions from the waste sector are the third largest anthropogenic source of methane, making up 13% of total global anthropogenic emissions. Current climate change mitigation policies emphasize the need to reduce methane emissions from municipal solid waste (MSW) landfills, as they are the primary contributors within the sector. The MSW landfill operational patterns in China, India, and the U.S. vary significantly. Effective operational practices at MSW landfills can significantly mitigate these emissions. Previous studies have estimated MSW landfill methane emission rates using bottom-up inventories and demonstrated the effectiveness of these practices through on-site experiments. However, few studies have focused on quantifying CH4 emission of landfills from space. In this study, we applied a two-tier observing framework to evaluate the influence of operational practices on methane emissions from a total of 90 MSW landfills in these three countries from space. Wind rotation analyses of Tropospheric Monitoring Instrument (TROPOMI) data was first conducted to qualitatively assess whether methane emissions from MSW landfills are a primary source of methane emissions in urban areas. Then, hyperspectral imager observations were used to quantify methane emission fluxes from these landfills. Methane emission rates derived from hyperspectral imagers for MSW landfills in India were found to be, on average, 1.3 times higher than estimates based on the IPCC default method. Overall, our results demonstrate that landfill operational practices in China are more effective in reducing methane emissions than those in India and the U.S. Additionally, a poor correlation (r = -0.39 for China, 0.21 for India, and -0.17 for the U.S.) was found between methane emission rates derived from hyperspectral imagers and those estimated using the IPCC default method, highlighting the need for long-term simultaneous satellite and on-site measurements to better understand the discrepancies.