title: Super-emitters in natural gas infrastructure are caused by abnormal process conditions.
abstract: Effectively mitigating methane emissions from the natural gas supply chain requires addressing the disproportionate influence of high-emitting sources. Here we use a Monte Carlo simulation to aggregate methane emissions from all components on natural gas production sites in the Barnett Shale production region (Texas). Our total emission estimates are two-thirds of those derived from independent site-based measurements. Although some high-emitting operations occur by design (condensate flashing and liquid unloadings), they occur more than an order of magnitude less frequently than required to explain the reported frequency at which high site-based emissions are observed. We conclude that the occurrence of abnormal process conditions (for example, malfunctions upstream of the point of emissions; equipment issues) cause additional emissions that explain the gap between component-based and site-based emissions. Such abnormal conditions can cause a substantial proportion of a site's gas production to be emitted to the atmosphere and are the defining attribute of super-emitting sites.
authors.affiliation: Environmental Defense Fund, 301 Congress Avenue, Suite 1300, Austin, Texas 78701, USA.
authors.forename: Daniel
authors.identifier: 0000-0002-8394-5725
authors.initials: D
authors.lastname: Zavala-Araiza
authors.affiliation: Environmental Defense Fund, 301 Congress Avenue, Suite 1300, Austin, Texas 78701, USA.
authors.forename: Ramón A
authors.initials: RA
authors.lastname: Alvarez
authors.affiliation: Environmental Defense Fund, 301 Congress Avenue, Suite 1300, Austin, Texas 78701, USA.
authors.forename: David R
authors.initials: DR
authors.lastname: Lyon
authors.affiliation: Center for Energy and Environmental Resources, The University of Texas at Austin, 10100 Burnet Road, Austin, Texas 78758, USA.
authors.forename: David T
authors.initials: DT
authors.lastname: Allen
authors.affiliation: Department of Mechanical Engineering, Colorado State University, Fort Collins, Colorado 80523, USA.
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Marchese
authors.affiliation: The Energy Institute, Colorado State University, Fort Collins, Colorado 80523, USA.
authors.forename: Daniel J
authors.identifier: 0000-0003-2832-048X
authors.initials: DJ
authors.lastname: Zimmerle
authors.affiliation: Environmental Defense Fund, 301 Congress Avenue, Suite 1300, Austin, Texas 78701, USA.
authors.forename: Steven P
authors.initials: SP
authors.lastname: Hamburg