Observations of ozone, acyl peroxy nitrates, and their precursors during summer 2019 at Carlsbad Caverns National Park, New Mexico

Carlsbad Caverns National Park (CAVE) is located in southeastern New Mexico and is adjacent to the Permian Basin, one of the most productive oil and natural gas (O&G) production regions in the United States. Since 2018, ozone (O-3) at CAVE has frequently exceeded the 70 ppbv 8-hour National Ambient Air Quality Standard. We examine the influence of regional emissions on O-3 formation using observations of O-3, nitrogen oxides (NOx = NO + NO2), a suite of volatile organic compounds (VOCs), peroxyacetyl nitrate (PAN), and peroxypropionyl nitrate (PPN). Elevated O-3 and its precursors are observed when the wind is from the southeast, the direction of the Permian Basin. We identify 13 days during the July 25 to September 5, 2019 study period when the maximum daily 8-hour average (MDA8) O-3 exceeded 65 ppbv; MDA8 O-3 exceeded 70 ppbv on 5 of these days. The results of a positive matrix factorization (PMF) analysis are used to identify and attribute source contributions of VOCs and NOx. On days when the winds are from the southeast, there are larger contributions from factors associated with primary O&G emissions; and, on high O-3 days, there is more contribution from factors associated with secondary photochemical processing of O&G emissions. The observed ratio of VOCs to NOx is consistently high throughout the study period, consistent with NOx-limited O-3 production. Finally, all high O-3 days coincide with elevated acyl peroxy nitrate abundances with PPN to PAN ratios > 0.15 ppbv ppbv(-1) indicating that anthropogenic VOC precursors, and often alkanes specifically, dominate the photochemistry.

Automated summary

Carlsbad Caverns National Park in New Mexico experiences high ozone levels, primarily influenced by the productive oil and gas industry in the nearby Permian Basin. The study found that ozone and its precursors are elevated when winds blow from the southeast, coming from the direction of the Permian Basin. Analysis of volatile organic compounds and nitrogen oxides revealed that primary emissions from oil and gas activities, as well as secondary photochemical processes, contribute to ozone formation. The presence of anthropogenic VOC precursors, particularly alkanes, dominates the photochemistry.