Methane Emissions from Natural Gas Production Sites in the United States: Data Synthesis and National Estimate.

We used site-level methane (CH) emissions data from over 1000 natural gas (NG) production sites in eight basins, including 92 new site-level CH measurements in the Uinta, northeastern Marcellus, and Denver-Julesburg basins, to investigate CH emissions characteristics and develop a new national CH emission estimate for the NG production sector. The distribution of site-level emissions is highly skewed, with the top 5% of sites accounting for 50% of cumulative emissions. High emitting sites are predominantly also high producing (>10 Mcfd). However, low NG production sites emit a larger fraction of their CH production. When combined with activity data, we predict that this creates substantial variability in the basin-level CH emissions which, as a fraction of basin-level CH production, range from 0.90% for the Appalachian and Greater Green River to >4.5% in the San Juan and San Joaquin. This suggests that much of the basin-level differences in production-normalized CH emissions reported by aircraft studies can be explained by differences in site size and distribution of site-level production rates. We estimate that NG production sites emit total CH emissions of 830 Mg/h (95% CI: 530-1200), 63% of which come from the sites producing <100 Mcfd that account for only 10% of total NG production. Our total CH emissions estimate is 2.3 times higher than the U.S. Environmental Protection Agency's estimate and likely attributable to the disproportionate influence of high emitting sites.