Methane Emissions Across a Diverse Set of Large Landfills in the United States and Canada

Methane emissions from the waste sector may represent a significant fraction of the global anthropogenic methane budget. However, few comprehensive studies across the broad landscape of waste operations exist to validate existing bottom-up models that underpin reporting programs and national inventories. In this study, we flew two airborne imaging spectrometers to map emissions at large landfills across 18 states in the U.S. and three provinces in Canada between 2016-2022. This technology is particularly sensitive to point source methane emissions and can geolocate source locations to within several meters. We observed point sources at a high fraction (52%) of sites and observed high emission persistence (60%), or point source detection frequency, at sites we surveyed multiple times. Airborne derived emissions correlate poorly with EPA reported emission and are on average higher, which could point to some issues with models that underpin reporting protocols. We validated imaging spectrometer aerial emission rates against the Scientific Aviation mass balance technique at 15 landfills, and find good agreement between these two independent measurement systems. Sustained measurements across many landfills and waste sites are needed to validate inventories and provide actionable data for industry operators and enforcement agencies.