Quantifying Methane and Ethane Emissions to the Atmosphere From Central and Western US Oil and Natural Gas Production Regions

We present atmospheric measurements of methane (CH4) and ethane (C2H6) taken aboard a National Oceanic and Atmospheric Administration WP-3D research aircraft in 2015 over oil- and natural gas-producing regions of the central and western United States. We calculate emission rates from the horizontal flux of CH4 and C2H6 in the planetary boundary layer downwind of five of these oil- and gas-producing regions: the Bakken in North Dakota, the Barnett in Texas, the Denver Basin in Colorado, the Eagle Ford in Texas, and the Haynesville in Texas and Louisiana. In general, we find that the enhancement of C2H6 relative to CH4 in the atmosphere is similar to their relative abundances in locally produced natural gas. For the Bakken and Barnett regions, both absolute CH4 emissions and the percentage of produced natural gas emitted to the atmosphere are consistent with previous studies. The percentage of produced natural gas emitted to the atmosphere was lower than in previous studies in the Denver Basin and the Haynesville regions, which may be due to a decrease in drilling activity, an increase in emission controls, or some combination thereof. Finally, we provide the first estimates of basin-wide emissions from the Eagle Ford region using in situ airborne data and find C2H6 emissions to be greater than those from the Bakken region. Emissions from the Bakken and Eagle Ford regions combined account for 20% of anthropogenic C2H6 emissions in North America.