Impact of energy production in the Barnett Shale gas region on the measuredambient hydrocarbon concentrations in Denton, Texas

Özet

The Barnett Shale play in North Texas is one of the largest active onshore shale gas regions in the United States.Over the past two decades, unconventional energy production from shale gas in North Texas has grown rapidly.The energy production peaked in 2012 and has declined since. The city of Denton is located at the edge of theBarnett Shale play and is within the Dallas-Fort Worth metropolitan area. In this paper, we describe a long-termtrend study of 84 total non-methane organic carbon (TNMOC) species measured at the Denton Airport Southmonitoring station, an exurban site. The annual mean TNMOC concentrations measured during 2000–2017increased by +8.03 ± 12.92 ppb-C/year (+12.75%/year). The year-to-year increase in the mean TNMOCconcentrations mirrored the energy production volume changes from natural gas wells and liquid condensatefacilities within 2-km from the ambient air quality monitoring station. Concentrations of alkanes increasedsignificantly, especially the natural gas species of ethane, propane, n-butane, and isobutane. The annual var-iations in the ethane concentrations were similar to changes observed in the natural gas and liquid condensateproduction from nearby wells. High levels of ethane, a dominant natural gas species, were originating fromregions with a higher density of gas wells within close proximity of the monitoring site. In contrast, the con-centrations of alkene and aromatic species have declined during the study period as a result of decreases fromtraditional urban emission sources. However, the trend in benzene, a carcinogenic aromatic species found invehicular and natural gas emissions, and xylene concentrations were similar to the n-alkane trend, suggesting theinfluence of energy production activities on key ambient aromatic compounds.