Air pollution from unconventional oil and gas development in the Eagle Ford Shale

Unconventional oil and gas development (UOGD) has experienced substantial growth in recent years with currently unconstrained impacts on air quality. In this work, we describe ambient aerosol and gas-phase measurements during spring 2021 to examine air quality in the Eagle Ford Shale (EFS), a region in southeast Texas with thousands of UOGD wells. NO_x, O₃, H₂S, PM₁, and several VOCs were measured at concentrations above expected levels for non-urban regions. Hydrocarbon measurements from gas chromatography (GC) and proton transfer reaction (PTR) mass spectrometry show periodic high concentrations of variable compositions consisting of both saturated and unsaturated (polycyclic and/or aromatic) hydrocarbons, including larger (C _> 10) unsaturated hydrocarbons that are often not quantified by GC measurements but are still present at substantial concentrations and relevant for air quality. Hydrocarbon VOCs are expected pollutants from anthropogenic activity and, based on ratios of i-pentane to n-pentane, xylene to benzene, and toluene to benzene, measured VOC ratios were characteristic of UOGD activity. Wind data and back-trajectory analyses show that air predominantly arrived from the S/SE, consistent with UOGD sources as well as shipping emissions from the Gulf of Mexico impacting air quality in the EFS. Analysis of diurnal trends at the site show hydrocarbon and NO_x accumulation overnight and highlight diurnal differences in oxidative conditions, with important implications for both SOA and O₃ formation. UOGD emissions impact the air quality in Karnes City and more broadly the EFS as well as the nearby urban area of San Antonio, which struggles to meet national air quality standards set by the Environmental Protection Agency.