title: Integrating Source Apportionment Tracers into a Bottom-up Inventory of Methane Emissions in the Barnett Shale Hydraulic Fracturing Region.
abstract: A growing dependence on natural gas for energy may exacerbate emissions of the greenhouse gas methane (CH4). Identifying fingerprints of these emissions is critical to our understanding of potential impacts. Here, we compare stable isotopic and alkane ratio tracers of natural gas, agricultural, and urban CH4 sources in the Barnett Shale hydraulic fracturing region near Fort Worth, Texas. Thermogenic and biogenic sources were compositionally distinct, and emissions from oil wells were enriched in alkanes and isotopically depleted relative to natural gas wells. Emissions from natural gas production varied in δ(13)C and alkane ratio composition, with δD-CH4 representing the most consistent tracer of natural gas sources. We integrated our data into a bottom-up inventory of CH4 for the region, resulting in an inventory of ethane (C2H6) sources for comparison to top-down estimates of CH4 and C2H6 emissions. Methane emissions in the Barnett are a complex mixture of urban, agricultural, and fossil fuel sources, which makes source apportionment challenging. For example, spatial heterogeneity in gas composition and high C2H6/CH4 ratios in emissions from conventional oil production add uncertainty to top-down models of source apportionment. Future top-down studies may benefit from the addition of δD-CH4 to distinguish thermogenic and biogenic sources.
authors.affiliation: †University of Cincinnati, Departments of Geology and Geography, Cincinnati, Ohio 45221, United States.
authors.forename: Amy
authors.initials: A
authors.lastname: Townsend-Small
authors.affiliation: ‡University of California, Irvine, Department of Chemistry, Irvine, California 92697, United States.
authors.forename: Josette E
authors.initials: JE
authors.lastname: Marrero
authors.affiliation: §Environmental Defense Fund, 301 Congress Ave., Suite 1300, Austin, Texas 78701, United States.
authors.forename: David R
authors.initials: DR
authors.lastname: Lyon
authors.affiliation: ‡University of California, Irvine, Department of Chemistry, Irvine, California 92697, United States.
authors.forename: Isobel J
authors.initials: IJ
authors.lastname: Simpson
authors.affiliation: ‡University of California, Irvine, Department of Chemistry, Irvine, California 92697, United States.
authors.forename: Simone
authors.initials: S
authors.lastname: Meinardi
authors.affiliation: ‡University of California, Irvine, Department of Chemistry, Irvine, California 92697, United States.
authors.forename: Donald R
authors.initials: DR
authors.lastname: Blake
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D002247:Carbon Isotopes; D004980:Ethane / Q000032:analysis; D005843:Geography; D019015:Geologic Sediments / Q000737:chemistry*; D000067071:Hydraulic Fracking; D006838:Hydrocarbons / Q000032:analysis; D008697:Methane / Q000032:analysis*; D059206:Natural Gas / Q000032:analysis; D061329:Oil and Gas Fields; D011407:Propane / Q000032:analysis; D013781:Texas
chemical_list: D000393:Air Pollutants; D002247:Carbon Isotopes; D006838:Hydrocarbons; D059206:Natural Gas; D004980:Ethane; D008697:Methane; D011407:Propane