title: Fugitive methane emissions from leak-prone natural gas distribution infrastructure in urban environments.
abstract: Fugitive emissions from natural gas systems are the largest anthropogenic source of the greenhouse gas methane (CH4) in the U.S. and contribute to the risk of explosions in urban environments. Here, we report on a survey of CH4 emissions from 100 natural gas leaks in cast iron distribution mains in Metro Boston, MA. Direct measures of CH4 flux from individual leaks ranged from 4.0 - 2.3 × 10(4) g CH4•day(-1). The distribution of leak size is positively skewed, with 7% of leaks contributing 50% of total CH4 emissions measured. We identify parallels in the skewed distribution of leak size found in downstream systems with midstream and upstream stages of the gas process chain. Fixing 'superemitter' leaks will disproportionately stem greenhouse gas emissions. Fifteen percent of leaks surveyed qualified as potentially explosive (Grade 1), and we found no difference in CH4 flux between Grade 1 leaks and all remaining leaks surveyed (p = 0.24). All leaks must be addressed, as even small leaks cannot be disregarded as 'safely leaking.' Key methodological impediments to quantifying and addressing the impacts of leaking natural gas distribution infrastructure involve inconsistencies in the manner in which gas leaks are defined, detected, and classified. To address this need, we propose a two-part leak classification system that reflects both the safety and climatic impacts of natural gas leaks.
authors.affiliation: Boston University, Department of Earth and Environment, 685 Commonwealth Avenue, Boston, MA, 02215, USA. Electronic address: hendricm@bu.edu.
authors.forename: Margaret F
authors.initials: MF
authors.lastname: Hendrick
authors.affiliation: Gas Safety, Inc., Southborough, MA, 01172, USA. Electronic address: bobackley@gassafetyusa.com.
authors.forename: Robert
authors.initials: R
authors.lastname: Ackley
authors.affiliation: Boston University, Department of Earth and Environment, 685 Commonwealth Avenue, Boston, MA, 02215, USA. Electronic address: baharsm@bu.edu.
authors.forename: Bahare
authors.initials: B
authors.lastname: Sanaie-Movahed
authors.affiliation: Boston University, Department of Earth and Environment, 685 Commonwealth Avenue, Boston, MA, 02215, USA. Electronic address: xjtang@bu.edu.
authors.forename: Xiaojing
authors.initials: X
authors.lastname: Tang
authors.affiliation: Boston University, Department of Earth and Environment, 685 Commonwealth Avenue, Boston, MA, 02215, USA. Electronic address: nathan@bu.edu.
authors.forename: Nathan G
authors.initials: NG
authors.lastname: Phillips
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D002947:Cities; D008697:Methane / Q000032:analysis*; D059206:Natural Gas / Q000032:analysis
chemical_list: D000393:Air Pollutants; D059206:Natural Gas; D008697:Methane
keywords: Distribution pipelines; Greenhouse gas; Methane; Natural gas