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Assessment of methane emissions from the U.S. oil and gas supply chain

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Science  13 Jul 2018:
Vol. 361, Issue 6398, pp. 186-188
DOI: 10.1126/science.aar7204
  • Fig. 1 Comparison of this work’s bottom-up (BU) estimates of methane emissions from oil and natural gas (O/NG) sources to top-down (TD) estimates in nine U.S. O/NG production areas.

    (A) Relative differences of the TD and BU mean emissions, normalized by the TD value, rank ordered by natural gas production in billion cubic feet per day (bcf/d, where 1 bcf = 2.8 × 107 m3). Error bars represent 95% confidence intervals. (B) Distributions of the nine-basin sum of TD and BU mean estimates (blue and orange probability density, respectively). Neither the ensemble of TD-BU pairs (A) nor the nine-basin sum of means (B) are statistically different [p = 0.13 by a randomization test, and mean difference of 11% (95% confidence interval of −17 to 41%)].

  • Table 1 Summary of this work’s bottom-up estimates of CH4 emissions from the U.S. oil and natural gas (O/NG) supply chain (95% confidence interval) and comparison to the EPA Greenhouse Gas Inventory (GHGI).

    Industry segment2015 CH4 emissions (Tg/year)
    This work (bottom-up)EPA GHGI (17)
    Production7.6 (+1.9/−1.6)3.5
    Gathering2.6 (+0.59/−0.18)2.3
    Processing0.72 (+0.20/−0.071)0.44
    Transmission and storage1.8 (+0.35/−0.22)1.4
    Local distribution*0.44 (+0.51/−0.22)0.44
    Oil refining and transportation*0.034 (+0.050/−0.008)0.034
    U.S. O/NG total13 (+2.1/−1.7)8.1 (+2.1/−1.4)

    *This work’s emission estimates for these sources are taken directly from the GHGI. The local distribution estimate is expected to be a lower bound on actual emissions and does not include losses downstream of customer meters due to leaks or incomplete combustion (materials and methods, section S1.5).

    †The GHGI only reports industry-wide uncertainties.

    Supplementary Materials

    • Assessment of methane emissions from the U.S. oil and gas supply chain

      Ramón A. Alvarez, Daniel Zavala-Araiza, David R. Lyon, David T. Allen, Zachary R. Barkley, Adam R. Brandt, Kenneth J. Davis, Scott C. Herndon, Daniel J. Jacob, Anna Karion, Eric A. Kort, Brian K. Lamb, Thomas Lauvaux, Joannes D. Maasakkers, Anthony J. Marchese, Mark Omara, Stephen W. Pacala, Jeff Peischl, Allen L. Robinson, Paul B. Shepson, Colm Sweeney, Amy Townsend-Small, Steven C. Wofsy, Steven P. Hamburg

      Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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      • Materials and Methods
      • Additional author disclosures
      • Figs. S1 to S11
      • Tables S1 to S12
      • References
      Database S1
      Supporting datasets to understand and assess the paper�s conclusions
      Database S2
      Shapefiles of top-down area boundaries used in this work

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