The Impact of Changes in Barometric Pressure on Landfill Methane Emission

On a global scale, landfill methane emissions contribute over 15% of the anthropogenic methane burden into the atmosphere. Quantitative understanding of methane emission from landfills and how environmental variables regulate the emission is essential for; (1) modeling studies, (2) determining the mitigation strategy, and (3) for formulating controls and regulations by government agencies. Here we present results from a recent study on the relationship between landfill methane emission and changes in barometric pressure. We used the eddy covariance method to continuously monitor methane flux and barometric pressure at Bluff Road Landfill near Lincoln, Nebraska from Jun to Dec, 2010. Our results show that the methane emission rate is strongly dependent on barometric pressure changes; i.e., rising atmospheric pressure suppresses the emission, while falling atmospheric pressure enhances the emission. We found that the phase angle between methane flux and barometric pressure to be around 110o on a weekly time scale. From our study, 8-day continuous emission measurements are needed to average out the impact of barometric pressure changes on landfill methane emissions. Our results also show that there are few seasonal variations in landfill methane emissions once the impact of changes in barometric pressure on the emissions is averaged out. This seems to suggest that the amount of methane that was kept inside the landfill during the time of rising barometric pressure probably diffused into the atmosphere during the time of falling pressure, and didn't get lost via oxidation. The winter methane emission rate was found to be slightly higher than that in summer, presumably because of a lower oxidation rate. Based on our results, we can conclude that short time interval measurements with techniques such as the trace plume method, mass balance method, or closed-chamber method will have large variations in measured emission rates because of the strong dependence of methane emissions on barometric pressure changes. Estimates of annual total landfill methane emissions based on those measurements will inevitably yield a large uncertainty, up to a factor of ten. A similar relationship between methane emission and changes in barometric pressure has been observed and reported from many studies over peatland, wetland and other ecosystems. Our results demonstrate that it is imperative to make continuous methane emission measurements over landfill, wetland and other ecosystems in order to correctly estimate the annual total methane emission.