Detection and long-term quantification of methane emissions from an active landfill

Abstract. Landfills are a significant source of fugitive methane (CH₄) emissions which should be precisely and regularly monitored to reduce and mitigate net greenhouse gas emissions. In this study, we present long-term in-situ near-surface mobile atmospheric CH₄ mole fraction measurements (complemented by meteorological measurements from a fixed station) from 21 campaigns that cover approximately four years from September 2016 to December 2020. These campaigns were utilized to regularly quantify the total CH₄ emissions from an active landfill in France. We use a simple atmospheric inversion approach based on a Gaussian plume dispersion model to derive CH₄ emissions. Together with the measurements near the soil surface mainly dedicated to the identification of sources within the landfill, measurements of CH₄ made on the landfill perimeter (near-field) helped us to provide some qualitative insights about the respective weight of the main areas of emissions. However, we hardly managed to extract a signal representative of the overall landfill emissions from these measurements, which limited our ability to derive robust estimates of the emissions when assimilating them in the atmospheric inversions. The analysis shows that the inversions based on the measurements from a remote road further away from the landfill (far-field) yielded more reliable estimates. According to these estimates, the total CH₄ emissions have a large temporal variability and range from ~0.4 t CH₄/d to ~7 t CH₄/d, with an average value of ~2.1 t CH₄/d. We find a weak negative correlation between these estimates of the CH₄ emissions and atmospheric pressure for the active landfill. However, this weak emission-pressure relationship is based on a relatively small sample of reliable emission estimates with large sampling gaps. More frequent robust estimations are required to better understand this relationship for an active landfill.