Synthesis of recent ground-level methane emission measurements from the U.S. natural gas supply chain

A synthesis of new methane (CH4) emission data from a recent series of ground-based field measurements shows that 1.7% of the methane in natural gas is emitted between extraction and delivery (with a 95% confidence interval from 1.3% to 2.2%). This synthesis was made possible by a recent series of methane emission measurement campaigns that focused on the natural gas supply chain, production through distribution. The new data were translated to a standard basis, augmented with other data sources as needed, and simulated using a Monte Carlo-enabled, life cycle model. Gathering facilities and production pneumatics are the top methane emission reduction opportunities for the natural gas sector, but there are knowledge gaps and sources of uncertainty that merit further research. In particular, “unassigned” emissions that were measured at the site level, as opposed to component-level emissions measured directly at the device level, account for 19% of supply chain methane emissions. By definition, unassigned emissions cannot be attributed to specific emission sources, and the current data do not provide insight into how they vary geographically. The inclusion of unassigned emissions makes the bottom-up compilation of emission sources more complete, but is a source of uncertainty that points to opportunities for further research. Further research should include geographically diverse measurement studies that provide a better understanding of regional variability and validate emission measurements by using a combination of component- and site-level measurements.