Improved estimations of waste-related methane emissions using satellite observations: a case study on a US landfill

Reducing methane (CH4) emissions offers the opportunity to slow down global temperature rise in the near term. More than 10 % of anthropogenic CH4 is emitted by the degradation of solid waste, when accumulated in open dumps or managed landfills. Methane production at solid waste sites depends upon various parameters, influenced by waste composition and amounts, landfill operation, as well as climate and meteorological variables. Therefore, landfill emissions are spatially and temporally heterogeneous, which challenges global mitigation efforts.  Atmospheric measurements from ground and aerial vehicles can be used to quantify and monitor emissions on a facility level. Large facilities located nearby densely populated areas are emission hotspots that can be detected with satellite instruments. We present a case study of the use of CH4 satellite data to derive emission estimates of the Miramar landfill in California, United States. We used observations from UNEP’s International Methane Emissions Observatory (IMEO), through its Methane Alert and Response System (MARS) to detect and quantify four CH4 plumes measured with EMIT satellite between August 2023 and August 2024. We characterized the landfill in terms of amounts and composition of waste, population served and development index, landfill management and gas capture infrastructure, as well as temperature and precipitations.   Estimated fluxes were 1.69 ± 0.85, 2.74 ± 1.38, 4.79 ± 2.41 t/h and 38.7 ± 19.4 t CH4/h. The exceptionally high maximum likely occurred while the gas collection system was down. The landfill operator declares a total amount of 20,790 t CH4 collected over the year 2023 and reports total emissions equivalent to 1.56 and 0.526 t CH4/h, based on the two US-EPA standards methods. The reported emissions and our observed estimate reveal substantial methane losses, despite apparent gas recovery efforts.  These inconsistencies, combined with the variability in satellite-derived fluxes, underscore the difficulty of aligning measurement methodologies. They highlight the need to integrate satellite observations, landfill operations data, and inventory models to refine methane emission estimates to support more effective mitigation strategies.  Our case further shows that atmospheric measurements and the analysis of landfill characteristics can be used in a global classification of facilities and to derive appropriate emission factors. We therefore identified opportunities brought by this measurement-based approach, going from small scale to larger scale: (1) to target efficient methane mitigation action at large-emitting facilities, (2) to quantify the efficiency of waste management policies, (3) to improve country-reported contributions. This research has been funded in the framework of UNEP’s IMEO.