Do shale oil and gas production activities impact ambient air quality? A comprehensive study of 12 years of chemical concentrations and well production data from the Barnett Shale region of Texas.

Starting around 2008, there was rapid expansion of oil and natural gas (ONG) production into more heavily populated areas within the Dallas-Fort Worth metroplex in the Barnett Shale region of Texas. This colocation raised concerns regarding the effect of ONG activities on chemical levels in the air. In the current study, we examined the potential impacts of ONG activity on the types and concentrations of chemicals in ambient air in the Barnett Shale. Volatile organic compound (VOC) concentrations from 6-12 years (2008-2019) of hourly ambient air monitoring data from 15 monitors (4 monitors had ≥ 10 years of data) were compared to several metrics of ONG activity (number of active wells, natural gas production, condensate production) within a 2-mile radius of each monitor. Monitoring sites were also classified into urban, suburban, and rural areas as a surrogate for nearby vehicular emission sources. Analyses of this huge dataset showed that both peak and mean chemical concentrations of lighter alkane hydrocarbons (e.g., ethane) were most impacted by the number of gas wells. Levels of heavier alkanes (e.g., pentane) were increased by condensate production and at monitors located in areas with greater urbanicity, and therefore higher vehicular emissions. The levels of unsaturated alkynes (e.g., ethylene) were entirely driven by urbanicity and were unaffected by nearby ONG activity. The same pattern was seen with the ratio of iso:n-pentane, which is contrary to the findings of others and suggests an area for future research. Aromatic hydrocarbons were impacted by multiple emissions sources and did not show the same patterns as non-aromatic VOCs. No VOC concentrations were at levels of concern for human health or odor based on comparison to Texas air monitoring comparison values. Overall, ONG activities impact air quality, but this must be evaluated in the context of other emission sources such as automobiles.