Estimating Methane Fluxes from Large Point Sources in New York State: A Methodological Intercomparison

The New York State Climate and Community Leaders Protection Act (CLCPA) was signed into law in 2019 as the first statute mandating greenhouse gas reductions in the United States. In contrast to most governmental or international reduction goals, the CLCPA specifically requires use of global warming potentials over 20-year horizons (GWP20) for accounting as opposed to the more commonly used 100-year potentials (GWP100). Therefore, characterizing and understanding in-state emissions of methane—with its decadal lifetime—has become extremely important in order to assist the state in meeting its statutory requirements. Here, we report a methodological intercomparison of recent stationary, mobile and remote measurements of methane within New York State to assist the state in meeting its CLPCA requirements. A comprehensive suite of in situ methane, ethane, CO2, CO, and N2O were taken over the past two years from various fixed surface, mobile van, and aircraft platforms around many major methane point sources in the state. These sites include landfills, sewage treatment plants, consolidated animal feedlot operations (CAFOs), and oil and gas infrastructure. We find that landfills are the largest individual point sources within the state, but that self-reported emissions to the national GreenHouse Gas Inventory are not consistent with the atmospheric observations; waste-in-place remains a better predictor of overall methane emissions for active landfills. We also find that mobile van measurements are capable of reproducing aircraft measurements of landfill fluxes, although boundary layer depth remains an uncertainty for either methodology (but especially the surface measurements). We additionally compare these in situ-estimated fluxes of methane emissions to fluxes inferred from satellite observations from TROPOMI and GHGsat, Inc.