Ozone and Precursors in the Permian Oil and Gas Basin

The Permian basin, spanning western Texas and southeastern New Mexico, is one of the largest and most productive oil and gas (O&G) regions in the United States. O&G production rates have surged by a factor of five over the last decade, raising regional air pollution concerns. We present findings from a series of special air quality studies conducted at Carlsbad Caverns National Park (CAVE), alongside an analysis of long-term (2007-2023) ground-level ozone (O3) trends from multiple measurement sites in the region. Located in the western Permian basin, CAVE has frequently experienced elevated summer O3 in excess of the National Ambient Air Quality Standards (NAAQS) level of 70 ppbv. Using quantile regression, we identify significant increasing trends in peak O3 (95th quantile of maximum daily 8-h averages) between 2007-2023 at CAVE (0.6 ppbv yr-1), as well as at the New Mexico cities of Carlsbad (0.9 ppbv yr-1) and Hobbs (0.5 ppbv yr-1). A multivariate quantile regression model suggests that the rising O3 is due to increasing regional precursor emissions, as meteorology and wildfire smoke influence alone fail to predict the observed trends. Ground-based observations of nitrogen oxides (NOx = NO + NO2) and a suite of volatile organic compounds (VOCs) collected at CAVE during the summers of 2019 and 2021 provide insight into the sensitivity of O3 production to precursor emissions. During both study periods, light alkane hydrocarbons commonly associated with O&G activity dominated the total VOC mixing ratio and reactivity towards hydroxyl radicals (OH). A photochemical box modeling analysis constrained with observations from the 2019 study indicates that local O3 production was approximately 1.5 times more sensitive to NOx than VOCs. While OMI and TROPOMI satellite data show a 1.8 % yr-1 increase in the summer average tropospheric nitrogen dioxide (NO2) column density over the Permian basin between 2007-2023, the formaldehyde (HCHO) column density and the HCHO/NO2 column ratio have decreased. This suggests that increases in NOx emissions are shifting O3 production towards less NOx-sensitive conditions.