title: Methane, Black Carbon, and Ethane Emissions from Natural Gas Flares in the Bakken Shale, North Dakota.
abstract: Incomplete combustion during flaring can lead to production of black carbon (BC) and loss of methane and other pollutants to the atmosphere, impacting climate and air quality. However, few studies have measured flare efficiency in a real-world setting. We use airborne data of plume samples from 37 unique flares in the Bakken region of North Dakota in May 2014 to calculate emission factors for BC, methane, ethane, and combustion efficiency for methane and ethane. We find no clear relationship between emission factors and aircraft-level wind speed or between methane and BC emission factors. Observed median combustion efficiencies for methane and ethane are close to expected values for typical flares according to the US EPA (98%). However, we find that the efficiency distribution is skewed, exhibiting log-normal behavior. This suggests incomplete combustion from flares contributes almost 1/5 of the total field emissions of methane and ethane measured in the Bakken shale, more than double the expected value if 98% efficiency was representative. BC emission factors also have a skewed distribution, but we find lower emission values than previous studies. The direct observation for the first time of a heavy-tail emissions distribution from flares suggests the need to consider skewed distributions when assessing flare impacts globally.
authors.affiliation: Climate and Space Sciences and Engineering, University of Michigan , Ann Arbor, Michigan 48109, United States.
authors.forename: Alexander
authors.identifier: http://orcid.org/0000-0003-1260-4744
authors.initials: A
authors.lastname: Gvakharia
authors.affiliation: Climate and Space Sciences and Engineering, University of Michigan , Ann Arbor, Michigan 48109, United States.
authors.forename: Eric A
authors.initials: EA
authors.lastname: Kort
authors.affiliation: Department of Energy Resources Engineering, Stanford University , Stanford, California 94305, United States.
authors.forename: Adam
authors.identifier: http://orcid.org/0000-0002-2528-1473
authors.initials: A
authors.lastname: Brandt
authors.affiliation: Cooperative Institute for Research in Environmental Science, University of Colorado , Boulder, Colorado 80309, United States.|NOAA ESRL Chemical Sciences Division , Boulder, Colorado 80305, United States.
authors.forename: Jeff
authors.initials: J
authors.lastname: Peischl
authors.affiliation: NOAA ESRL Chemical Sciences Division , Boulder, Colorado 80305, United States.
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Ryerson
authors.affiliation: NOAA ESRL Chemical Sciences Division , Boulder, Colorado 80305, United States.
authors.forename: Joshua P
authors.initials: JP
authors.lastname: Schwarz
authors.affiliation: Climate and Space Sciences and Engineering, University of Michigan , Ann Arbor, Michigan 48109, United States.
authors.forename: Mackenzie L
authors.initials: ML
authors.lastname: Smith
authors.affiliation: Cooperative Institute for Research in Environmental Science, University of Colorado , Boulder, Colorado 80309, United States.
authors.forename: Colm
authors.initials: C
authors.lastname: Sweeney
mesh_terms: D000393:Air Pollutants; D002244:Carbon; D004980:Ethane; D008697:Methane; D059206:Natural Gas; D009658:North Dakota
chemical_list: D000393:Air Pollutants; D059206:Natural Gas; D002244:Carbon; D004980:Ethane; D008697:Methane