Influence of oil and gas field operations on spatial and temporal distributions of atmospheric non-methane hydrocarbons and their effect on ozone formation in winter

Abstract. Emissions from oil and natural gas development during winter in the Upper Green River basin of Wyoming are known to drive episodic ozone (O₃) production. Contrasting O₃ distributions were observed in the winters of 2011 and 2012, with numerous episodes (hourly O₃ ≥ 85 ppbv) in 2011 compared to none in 2012. The lack of O₃ episodes in 2012 coincided with a reduction in measured ambient levels of total non-methane hydrocarbons (NMHC). Measurements of speciated NMHC, and other air quality parameters, were performed to better understand emission sources and to determine which compounds are most active in promoting O₃ formation. Positive matrix factorization (PMF) analyses of the data were carried out to help achieve these goals. PMF analyses revealed three contributing factors that were identified with different emission source types: factor 1, combustion/traffic; factor 2, fugitive natural gas; and factor 3, fugitive condensate. Compositional signatures of the three contributing factors were identified through comparison with independently derived emission source profiles. Fugitive emissions of natural gas and of condensate were the two principal emission source types for NMHC. A water treatment and recycling facility was found to be a significant source of NMHC that are abundant in condensate, in particular toluene and m+p-xylene. Emissions from water treatment have an influence upon peak O₃ mixing ratios at downwind measurement sites.