Investigating the impacts of power plants, oil and gas operations, and biogenic emissions on ozone production in San Antonio

San Antonio, TX is the 8^th largest city in the United States and has recently been designated as in non-attainment of the 8-hour EPA ozone standard. Unlike Houston, ozone photochemistry in San Antonio has not been well-characterized, despite its mixture of biogenic, mobile, power plant, and oil and gas emissions from the nearby Eagle Ford Shale Play. Here, we use in situ observations made during the San Antonio Field Study in May 2017 along with output from CMAQ and a 0D box model to explore ozone production in the region. We find that ozone production in the outskirts of the city is almost exclusively NOx-limited, with median ozone production rates of 4 ppb/hr. In contrast, though still predominantly NO_X-limited, downtown San Antonio can have significant ozone production (> 15 ppb/hr) in the VOC-limited regime. Using four separate chemical mechanisms, we show that peroxy radicals from biogenic VOCs, particularly isoprene, and HO₂ are the dominant RO₂ species for ozone production, with almost negligible contributions from alkanes and aromatics. Using CMAQ, we estimate the contribution of power plant emissions to ozone concentrations in San Antonio, and, in particular, we investigate the potential impact of reductions in emissions from the Calaveras Lake power plants. In addition, we explore the impact of oil and gas emissions on ozone production in the region.