A109-06
Using ACT-America Ethane Data to Constrain Oil and Gas Methane Emissions Across the Southcentral and Eastern United States

Friday, 11 December 2020: 04:38
Virtual
Zachary Barkley1, Kenneth J Davis2, Yuyan Cui3, Sha Feng3, Alan Fried4, Joshua P DiGangi5, Scot M Miller6, James Walega4, Dirk Richter4, Petter Weibring4, Maximilian Eckl7, Anke Roiger8, Alina Fiehn8 and Julian Kostinek9, (1)Pennsylvania State University Main Campus, University Park, PA, United States, (2)The Pennsylvania State University, University Park, PA, United States, (3)The Pennsylvania State University, Department of Meteorology and Atmospheric Science, University Park, PA, United States, (4)University of Colorado at Boulder, Institute of Arctic and Alpine Research, Boulder, CO, United States, (5)NASA Langley Research Center, Hampton, VA, United States, (6)Harvard University, School of Engineering and Applied Sciences, Cambridge, MA, United States, (7)German Aerospace Center (DLR) Oberpfaffenhofen, Institute of Atmospheric Physics, Wessling, Germany, (8)Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institute of Atmospheric Physics, Oberpfaffenhofen, Germany, (9)German Aerospace Center Oberpfaffenhofen, Institute of Atmospheric Physics, Oberpfaffenhofen-Wessling, Germany
Recorded Presentation
Abstract:
According to the United States Environmental Protection Agency (EPA), methane (CH4) emissions from the oil and gas (O&G) sector contributed 28% (9 Tg) of anthropogenic CH4 emissions in the US in 2018. Top-down studies of O&G basins have disputed this number, estimating emissions that are larger than EPA-projected values. In addition to CH4 emissions, leaks in O&G infrastructure co-emit ethane (C2H6) and are responsible for more than 95% of C2H6 emissions in the US, making it an ideal tracer for identifying emissions originating from O&G sources. In this study we analyze more than 300 hours of continuous boundary layer C2H6 data collected during the Atmospheric Carbon and Transport - America (ACT-America) aircraft campaign across the central and eastern US, and use the dataset to infer CH4 emissions from the O&G sector. A C2H6 emissions inventory is created by multiplying the EPA 2012 Gridded CH4 Emissions Inventory O&G sector by observed C2H6/CH4 ratios, creating a prior C2H6 emissions inventory representing a best-guess of EPA-projected C2H6 emissions. Influence functions are created using FLEXPART for C2H6 observations collected from 91 flights across 4 seasons, and an atmospheric inversion is run to create a posterior C2H6 emissions map for each season. The posterior map for each season is averaged together and represent our best guess of the true C2H6 emissions across the central and eastern US. Differences between the posterior and prior C2H6 inventory represent potential errors in bottom-up estimates of O&G CH4 emissions. Overall, this study finds that CH4 emissions are underestimated by 50% in the southcentral US and western Appalachian. Strong correlations (r=0.8) between the observed C2H6 enhancements and the modeled posterior simulation demonstrate the utility of using a tracer whose emissions are dominated entirely by the O&G sector, a single, spatially-understood source, to solve for their emissions. Better documentation of C2H6/CH4 characteristics for O&G basins would provide greater confidence in translating O&G C2H6 emissions to an overall leak rate.
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