Seasonal landfill methane emissions driven by temperature and pressure

More than a quarter of anthropogenic global warming has been attributed to methane growth in the atmosphere. Landfills account for 17 % of estimated methane emissions in the United States of America (USA), according to the Environmental Protection Agency (EPA), but studies show that many landfills emit more than reported. We developed a novel method to calculate monthly methane emissions from an active landfill using atmospheric methane mixing ratios observed from a single tower in New Jersey, USA. The tower method provides two and a half years of semi-continuous measurements and therefore observes more of the variability of methane emissions and lacks the sampling bias present in other methods. Time-specific comparison of tower-based methane emissions against those observed from summertime aircraft sampling and year-round mobile ground-based platforms showed good agreement. Estimated methane emissions for 2023 were five times greater than those reported to the EPA. We observed a strong seasonality in methane emissions, with a peak in the winter and a minimum in the summer. This seasonal cycle was driven by a strong negative dependence on air temperature and the change in atmospheric pressure. Our results highlight the importance of observations in non-ideal weather conditions (such as declining pressure and near-freezing temperatures) when methane emissions are largest. We suggest that this methodology could be applied to other suitable landfills to improve estimates of methane emissions.