Development of a low-maintenance measurement approach to continuously estimate methane emissions: A case study.

The chemical breakdown of organic matter in landfills represents a significant source of methane gas (CH). Current estimates suggest that landfills are responsible for between 3% and 19% of global anthropogenic emissions. The net CH emissions resulting from biogeochemical processes and their modulation by microbes in landfills are poorly constrained by imprecise knowledge of environmental constraints. The uncertainty in absolute CH emissions from landfills is therefore considerable. This study investigates a new method to estimate the temporal variability of CH emissions using meteorological and CH concentration measurements downwind of a landfill site in Suffolk, UK from July to September 2014, taking advantage of the statistics that such a measurement approach offers versus shorter-term, but more complex and instantaneously accurate, flux snapshots. Methane emissions were calculated from CH concentrations measured 700m from the perimeter of the landfill with observed concentrations ranging from background to 46.4ppm. Using an atmospheric dispersion model, we estimate a mean emission flux of 709μgms over this period, with a maximum value of 6.21mgms, reflecting the wide natural variability in biogeochemical and other environmental controls on net site emission. The emissions calculated suggest that meteorological conditions have an influence on the magnitude of CH emissions. We also investigate the factors responsible for the large variability observed in the estimated CH emissions, and suggest that the largest component arises from uncertainty in the spatial distribution of CH emissions within the landfill area. The results determined using the low-maintenance approach discussed in this paper suggest that a network of cheaper, less precise CH sensors could be used to measure a continuous CH emission time series from a landfill site, something that is not practical using far-field approaches such as tracer release methods. Even though there are limitations to the approach described here, this easy, low-maintenance, low-cost method could be used by landfill operators to estimate time-averaged CH emissions and their impact downwind by simultaneously monitoring plume advection and CH concentrations.