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# Reconciling divergent estimates of oil and gas methane emissions

## Author(s): Zavala-Araiza, Daniel; Lyon, David R.; Alvarez, Ramón A.; Davis, Kenneth J.; Harriss, Robert; et al

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 Abstract: Published estimates of methane emissions from atmospheric data (top-down approaches) exceed those from source-based inventories (bottom-up approaches), leading to conflicting claims about the climate implications of fuel switching from coal or petroleum to natural gas. Based on data from a coordinated campaign in the Barnett Shale oil and gas-producing region of Texas, we find that top-down and bottom-up estimates of both total and fossil methane emissions agree within statistical confidence intervals (relative differences are 10% for fossil methane and 0.1% for total methane). We reduced uncertainty in top-down estimates by using repeated mass balance measurements, as well as ethane as a fingerprint for source attribution. Similarly, our bottom-up estimate incorporates a more complete count of facilities than past inventories, which omitted a significant number of major sources, and more effectively accounts for the influence of large emission sources using a statistical estimator that integrates observations from multiple ground-based measurement datasets. Two percent of oil and gas facilities in the Barnett accounts for half of methane emissions at any given time, and high-emitting facilities appear to be spatiotemporally variable. Measured oil and gas methane emissions are 90% larger than estimates based on the US Environmental Protection Agency’s Greenhouse Gas Inventory and correspond to 1.5% of natural gas production. This rate of methane loss increases the 20-y climate impacts of natural gas consumed in the region by roughly 50%. Electronic Publication Date: 7-Dec-2015 Citation: Zavala-Araiza, Daniel, Lyon, David R, Alvarez, Ramón A, Davis, Kenneth J, Harriss, Robert, Herndon, Scott C, Karion, Anna, Kort, Eric Adam, Lamb, Brian K, Lan, Xin, Marchese, Anthony J, Pacala, Stephen W, Robinson, Allen L, Shepson, Paul B, Sweeney, Colm, Talbot, Robert, Townsend-Small, Amy, Yacovitch, Tara I, Zimmerle, Daniel J, Hamburg, Steven P. (Reconciling divergent estimates of oil and gas methane emissions. Proceedings of the National Academy of Sciences, 201522126 - 201522126. doi:10.1073/pnas.1522126112 DOI: doi:10.1073/pnas.1522126112 ISSN: 0027-8424 EISSN: 1091-6490 Pages: 201522126 - 201522126 Type of Material: Journal Article Journal/Proceeding Title: Proceedings of the National Academy of Sciences Version: Final published version. This is an open access article.

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