Overview:

To realize immediate net climate benefits from the substitution of coal, diesel or gasoline with natural gas, the rate of methane loss from the entire natural gas supply chain must be less than a few percent. Since the natural gas supply chain consists of a vast network of infrastructure with countless emission sources, quantifying the total methane emissions from the U.S. natural gas supply chain represents a major challenge.  In this study, facility-level methane emissions measurements were conducted at 130 natural gas gathering facilities and processing plants in 13 U.S. states.  The results from the field campaign were combined with state and national facility databases in a Monte Carlo simulation to estimate methane emissions from U.S. natural gas gathering and processing operations. Total annual methane emissions of 2,421 (+245/-237) Gg were estimated for all U.S. gathering and processing operations, representing a methane loss rate of 0.47% (±0.05%) when normalized by annual methane production.  The methane emissions from gathering facilities were eight times that of previous EPA Greenhouse Gas Inventory (GHGI) estimates.  In April 2016, the EPA GHGI was updated based directly on the results of this study and gathering operations are now estimated to account for 27% of all methane emissions from natural gas supply chain.  In 2018, the results of this study were incorporated into a new national methane emissions model recently published in Science, which suggests that the total methane loss rate from all U.S. natural gas operations is 2.3% in comparison to the current EPA estimate of 1.4%.