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Energy and the Environment
Methane emissions from natural gas production sites in the United States: Data synthesis and national estimate Mark Omara, Naomi Zimmerman, Melissa R. Sullivan, Xiang Li, Aja Ellis, Rebecca Cesa, R Subramanian, Albert A Presto, and Allen L. Robinson Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b03535 • Publication Date (Web): 26 Sep 2018 Downloaded from http://pubs.acs.org on September 27, 2018
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Environmental Science & Technology
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Methane emissions from natural gas production sites in the United
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States: Data synthesis and national estimate
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Mark Omara*,†, Naomi Zimmermanⱡ, Melissa R. Sullivan, Xiang Li§, Aja Ellis,
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Rebecca Cesa, R. Subramanian, Albert A. Presto, and Allen L. Robinson
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Center for Atmospheric Particle Studies, Department of Mechanical Engineering, Carnegie
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Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213
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Abstract
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We used site-level methane (CH4) emissions data from over 1,000 natural gas (NG) production
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sites in eight basins, including 92 new site-level CH4 measurements in the Uinta, northeastern
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Marcellus, and Denver-Julesburg basins, to investigate CH4 emissions characteristics and
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develop a new national CH4 emission estimate for the NG production sector. The distribution of
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site-level emissions is highly skewed, with the top 5% of sites accounting for 50% of cumulative
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emissions. High emitting sites are predominantly also high producing (>10 Mcfd). However, low
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NG production sites emit a larger fraction of their CH4 production. When combined with activity
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data, we predict that this creates substantial variability in the basin-level CH4 emissions which,
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as a fraction of basin-level CH4 production, range from 0.90% for the Appalachian and Greater
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Green River to > 4.5% in the San Juan and San Joaquin. This suggests that much of the basin-
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level differences in production-normalized emissions reported by aircraft studies can be
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explained by differences in site size and distribution of site-level production rates. We estimate
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that NG production sites emit total CH4 emissions of 830 Mg/h (95% CI: 530—1,200), 63% of
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which come from the sites producing 100%. These
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eight sites were sampled offsite using the downwind plume measurements approaches utilizing
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Gaussian plume inverse modeling. It is possible that the measured CH4 emissions exceeding
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100% of CH4 production was due to offsite CH4 sources (e.g., biogenic CH4 source, CH4 from
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collocated equipment such as abandoned well, etc.). The exclusion of these eight sites from the
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consolidated database does not change our results: if we include them in our analysis, the total
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production CH4 emissions increases by
