Analysis of Oil and Gas Ethane and Methane Emissions in the Southcentral
and Eastern United States Using Four Seasons of Continuous Aircraft
Ethane Measurements
Abstract
In the last decade, much work has been done to better understand methane
(CH4) emissions from the oil and gas (O&G) industry in the United
States. Ethane (C2H6), a gas that is co-emitted with thermogenic sources
of CH4 , is emitted in the US almost entirely by the O&G sector. In
this study, we perform an inverse analysis on 300 hours of atmospheric
boundary layer C2H6 measurements to estimate C2H6 emissions from the US
O&G sector. Measurements were collected from 2017-2019 as part of the
Atmospheric Carbon and Transport (ACT) America aircraft campaign and
encompass much of the central and eastern United States. We find that
for the fall, winter, and spring campaigns, C2H6 data consistently
exceeds values that would be expected based on EPA O&G leak rate
estimates. C2H6 observations from the summer 2019 dataset show
significantly lower C2H6 enhancements in the southcentral region that
cannot be reconciled with data from the other three seasons, either due
to complex meteorological conditions or a temporal shift in the
emissions. Converting the fall, winter, and spring season posterior C2H6
emissions estimate to an inventory of O&G CH4 emissions, we estimate
that O&G CH4 emissions are larger than EPA inventory values by more
than 50%. Uncertainties in the gas composition data limit the
effectiveness of using C2H6 as a proxy for O&G CH4 emissions. These
limits could be resolved retroactively by increasing the availability of
industry-collected gas composition data.