New Insights for Estimating Diurnal Methane Emissions from Landfills

Methane is a short-lived yet extremely potent greenhouse gas in the atmosphere. Methane currently accounts for about one-third of global warming attributed to all greenhouse gases. Landfills, which are the third-largest source of methane emissions, are estimated to emit about 50% more methane than reported by the U.S. Environmental Protection Agency (U.S. EPA) inventory. While some landfills estimate emissions based on waste volume and other specific data, others rely on methane capture and operational information. A previous study on 70 high-emitting landfills in the U.S. revealed that their actual emissions were 77% higher than reported to the EPA. Among the 38 facilities that captured gas, their emissions were, on average, 200% greater than reported. Thus, a more accurate landfill methane emission estimate will have significant impact on our understanding on total atmospheric methane concentrations.

Recent advancements in quantifying landfill emissions reveal that traditional waste decay models are inaccurate for emission estimations due to spatial and temporal variability. Consequently, short-term measurements often fail to represent diurnal average emissions, especially in landfills without gas collection systems. Analyzing the 2020 U.S. EPA Landfill Database, we found that almost 41% of landfills lack gas collection systems. Using the Weather Research and Forecasting model, we simulated barometric pressure over 2267 unique landfills for April 2020. We found that changes in barometric pressure impact methane emissions, with 99% of landfills having more days with higher emissions between 10 AM and 4 PM than other times of the day. This suggests that short-term measurements during these hours, commonly used in field measurements, may overestimate diurnal average emissions, particularly in the absence of gas collection systems. Utilizing an unsaturated soil model, we estimated emission overestimation / underestimation under extreme barometric pressure conditions. Our soil model indicates that emissions measured between 10 AM and 4 PM could be overestimated by up to 25% of their average values. These findings underscore the need for continuous measurements or corrections in short-term emissions to accurately represent diurnal averages for annual greenhouse gas inventories.

For future direction, we aim to fill critical gaps in understanding open waste landfill methane emissions, globally, and improve the accuracy of the atmospheric chemistry models by improving the emission estimations. By providing more accurate estimates of methane emissions from landfills, we will support climate policy development, improve public health outcomes, and advance scientific research.