Seasonal Variation in Volatile Organic Compound Emissions and Secondary Organic Aerosol Formation from Unconventional Oil and Gas Development in the Eagle Ford Shale

Unconventional oil and gas development (UOGD) emits complex mixtures of volatile organic compounds (VOCs) that can be oxidized to form secondary pollutants, yet the full scope and fate of these emissions remain poorly understood. We measured gas- and particle-phase pollutants in the spring (March-May) and fall (October-November) in Karnes City (site coordinates: 28.8804, -97.8881), a rural town located within the Eagle Ford Shale, a large UOGD production region. We measured alkanes and aromatics, markers of UOGD activity, and found higher concentrations in the fall, likely due to slower photochemical processing and lower wind speeds. Non-targeted measurements of VOCs with a Vocus 2R proton transfer reaction time-of-flight mass spectrometer revealed large compounds whose contributions to secondary organic aerosol (SOA) are often not accounted for in atmospheric models. Additionally, we measured total and non-refractory submicron particulate matter (PM 1 ). Positive matrix factorization (PMF) indicated that 84% of the organic aerosol was oxygenated and aged, and concentrations were highest when wind was from areas of high oil well density north/northeast of the site. Additionally, increases in alkane concentrations often preceded increases in organic aerosol, consistent with UOGD emissions contributing to SOA formation. This work compares spring and fall 2023 measurements to spring 2021 measurements at the same site. Average PM 1 concentrations in the spring (2023: 6.7 μg m -3 ; 2021: 7.6 μg m -3 ) were double that of fall 2023 (3.4 μg m -3 ), consistent with enhanced photochemical processing from higher springtime solar irradiance.