Estimating methane emissions from Canadian landfills using aircraft measurements

Uncertainties in modeled and reported landfill emission inventories inspired aircraft-based measurements of CH₄ emissions from 21 Canadian landfills in November 2022 in the provinces of Alberta, Ontario, and Québec. We used mass balance equations to estimate emissions from ascending loop measurements and an inverted Gaussian dispersion method for downwind transect data. The results confirmed that the Canadian landfills are relatively low-emitting sites with emission estimates ranging from 4.8 kg/hr to 343.2 kg/hr, with a median of 73.7 kg/hr. Differences between measurement-based emission estimates and inventory values were also observed as expected, particularly for the five Alberta landfills that showed measurement-based estimates consistently lower than available inventory realizations (federal FOD model estimates, or operator-submitted values). This difference between measured and expected was not related to the flux magnitude or the size of the landfill. In addition, the results showed no correlation between landfill emissions and the amount of waste in place or mean annual temperature, and landfill emissions were weakly correlated to landfill area and annual cumulative precipitation. This study also highlights that in Canada, the federal and provincial regulators do not have reliable, complete, and accurate data for most landfills. Public databases are also practically non-existent. This lack of essential information limits our understanding of methane emissions from landfills, but the new federal regulation and reporting could help fill this gap. At last, in Canada, there is a need for more measurement-based monitoring not only to compare with inventory estimates, but also to ensure the efficacy of emissions mitigation practices.