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Southeastern New Mexico's Carlsbad Caverns National Park (CAVE) has increasingly experienced summertime ozone (O3) exceeding an 8‐hr average of 70 parts per billion by volume (ppbv). The park is located in the western part of the Permian oil and natural gas (O&G) basin, where production rates have increased fivefold in the last decade. We investigate O3–precursor relationships by constraining the F0AM box model to observations of nitrogen oxides (NOx = NO + NO2) and a suite of volatile organic compounds (VOCs) collected at CAVE during summer 2019. O&G‐related VOCs dominated the calculated VOC reactivity with hydroxyl radicals (OH) on days when O3 concentrations were primarily controlled by local photochemistry. Radical budget analysis showed that NOx levels were high enough to impose VOC sensitivity on O3 production in the morning hours, while subsequent NOx loss through photochemical consumption led to NOx‐sensitive conditions in the afternoon. Maximum daily O3 was responsive to both NOx and O&G‐related VOC reductions, with NOx reductions proving most effective. The model underestimated observed O3 during a 5‐day high O3 episode that was influenced by photochemically aged O&G emissions, as indicated by back‐trajectory analysis, low i‐/n‐pentane ratios, enhanced secondary VOCs, and low ratios of NOx to total reactive oxidized nitrogen (NOy). Model‐observation agreement was improved by constraining model NOx with observed NOy, which approximates NOx at the time of emission, indicating that a large fraction of O3 during this episode was formed nonlocally. Plain Language Summary: New Mexico's Carlsbad Caverns National Park has faced an increase in ground‐level ozone pollution. Summertime southeasterly winds place the park directly downwind of the Permian basin, one of the largest and most productive oil and natural gas (O&G) basins in the US. Our study, conducted using measurements collected in the park during summer 2019 and an air quality model, investigates how emissions from O&G activities affect ozone production. We find that local ozone production is sensitive to changes in both nitrogen oxides and volatile organic compound levels, but more significant reductions in ozone can be achieved by preferentially lowering nitrogen oxides. While the Permian is the closest O&G basin to the park, controlling ozone pollution may require emission reductions from other basins and shale plays in the region, as the park is sometimes impacted by aged air masses that transport ozone from farther upwind. Key Points: 8‐hr ozone concentrations frequently exceed 70 parts per billion by volume at Carlsbad Caverns National ParkA box modeling analysis indicates that local ozone production is most sensitive to nitrogen oxide levelsA subset of high ozone days was influenced by photochemically aged air masses carrying ozone from upwind oil and gas production regions [ABSTRACT FROM AUTHOR]

We present emission measurements of volatile organic compounds (VOCs) for western U.S. wildland fires made on the NSF/NCAR C‐130 research aircraft during the Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen (WE‐CAN) field campaign in summer 2018. VOCs were measured with complementary instruments onboard the C‐130, including a proton‐transfer‐reaction time‐of‐flight mass spectrometer (PTR‐ToF‐MS) and two gas chromatography (GC)‐based methods. Agreement within combined instrument uncertainties (<60%) was observed for most co‐measured VOCs. GC‐based measurements speciated the isomeric contributions to selected PTR‐ToF‐MS ion masses and generally showed little fire‐to‐fire variation. We report emission ratios (ERs) and emission factors (EFs) for 161 VOCs measured in 31 near‐fire smoke plume transects of 24 specific individual fires sampled in the afternoon when burning conditions are typically most active. Modified combustion efficiency (MCE) ranged from 0.85 to 0.94. The measured campaign‐average total VOC EF was 26.1 ± 6.9 g kg−1, approximately 67% of which is accounted for by oxygenated VOCs. The 10 most abundantly emitted species contributed more than half of the total measured VOC mass. We found that MCE alone explained nearly 70% of the observed variance for total measured VOC emissions (r2 = 0.67) and >50% for 57 individual VOC EFs representing more than half the organic carbon mass. Finally, we found little fire‐to‐fire variability for the mass fraction contributions of individual species to the total measured VOC emissions, suggesting that a single speciation profile can describe VOC emissions for the wildfires in coniferous ecosystems sampled during WE‐CAN. Key Points: A total of 161 measured volatile organic compound emission factors is 26.1 ± 6.9 g kg−1, 67% of which is from oxygenated species76% of the total volatile organic compound emitted mass shows statistically significant dependence on modified combustion efficiencyMass fraction contributions of individual species to the total measured emissions have little variability in 24 western U.S. fires [ABSTRACT FROM AUTHOR]

The Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen (WE‐CAN) deployed the NSF/NCAR C‐130 aircraft in summer 2018 across the western U.S. to sample wildfire smoke during its first days of atmospheric evolution. We present a summary of a subset of reactive oxidized nitrogen species (NOy) in plumes sampled in a pseudo‐Lagrangian fashion. Emissions of nitrogen oxides (NOx = NO + NO2) and nitrous acid (HONO) are rapidly converted to more oxidized forms. Within 4 h, ∼86% of the ΣNOy is in the form of peroxy acyl nitrates (PANs) (∼37%), particulate nitrate (pNO3) (∼27%), and gas‐phase organic nitrates (Org N(g)) (∼23%). The average e‐folding time and distance for NOx are ∼90 min and ∼40 km, respectively. Nearly no enhancements in nitric acid (HNO3) were observed in plumes sampled in a pseudo‐Lagrangian fashion, implying HNO3‐limited ammonium nitrate (NH4NO3) formation, with one notable exception that we highlight as a case study. We also summarize the observed partitioning of NOy in all the smoke samples intercepted during WE‐CAN. In smoke samples intercepted above 3 km above sea level (ASL), the contributions of PANs and pNO3 to ΣNOy increase with altitude. WE‐CAN also sampled smoke from multiple fires mixed with anthropogenic emissions over the California Central Valley. We distinguish samples where anthropogenic NOx emissions appear to lead to an increase in NOx abundances by a factor of four and contribute to additional PAN formation. Key Points: NOx and HONO are rapidly converted to other species. The average e‐folding time (distance) for NOx is ∼90 min (∼40 km)In 4 h, PANs contribute ∼37% of the ΣNOy species in smoke; pNO3 is the second largest (∼27%) contributorIn 4 h, Org N(g) constitute a large portion (∼23%) of the ΣNOy in the plumes sample during WE‐CAN [ABSTRACT FROM AUTHOR]

High abundance and strong light absorption of atmospheric brown carbon (BrC) have been reported in East Asia, especially in northern China. However, the molecular‐level understanding of BrC chromophores in this area is still limited and quite challenging. In this study, elemental composition of individual BrC chromophores was first investigated in the megacity of Beijing, China, using a powerful platform for the characterization of BrC chromophores, with combination of high‐performance liquid chromatography coupled to a UV/Vis absorbance detector and a time‐of‐flight mass spectrometer with an electrospray ionization source. The results from this study showed that S‐containing compounds (e.g., CHOS and CHONS) significantly increased in highly polluted days compared to lightly polluted days, probably due to increased emissions from sources such as coal combustion and favorable conditions for organosulfates formation. It was found that CHON and CHO compounds were the most abundant water‐soluble organic compounds in Beijing especially during the wintertime. Nitroaromatic compounds were the major water‐soluble BrC chromophores, with three major BrC chromophores (e.g., C6H5NO3, C7H7NO4, and C6H5NO4) found under all conditions, while other specific BrC chromophores with CHON‐ and CHO‐containing elemental formulas identified and varied in different seasons and pollution conditions. Overall, the water‐soluble BrC chromophores identified in this study explained about 2%–18% of the bulk BrC absorbance over the wavelength range of 300–400 nm. In‐depth studies on exploring more BrC chromophores as well as their chemical structures, related sources, and formation mechanisms should be conducted in the future. Key Points: S‐containing water‐soluble organic compounds were more enriched in highly polluted days both in winter and summerNitroaromatic compounds were identified as major water‐soluble brown carbon chromophores in BeijingC6H5NO3, C7H7NO4, and C6H5NO4 were three major brown carbon chromophores observed common across different seasons and pollution levels [ABSTRACT FROM AUTHOR]

Recent modeling and field studies have highlighted a relationship between sulfate concentrations and secondarily formed organic aerosols related to isoprene and other volatile biogenic gaseous emissions. The relationship between these biogenic emissions and sulfate is thought to be primarily associated with the effect of sulfate on aerosol acidity, increased aerosol water at high relative humidities, and aerosol volume. The Interagency Monitoring of Protected Visual Environments (IMPROVE) program provides aerosol concentration levels of sulfate (SO4) and organic carbon (OC) at 136 monitoring sites in rural and remote areas of the United States over time periods of between 15 and 28 years. This data set allows for an examination of relationships between these variables over time and space. The relative decreases in SO4 and OC were similar over most of the eastern United States, even though concentrations varied dramatically from one region to another. The analysis implied that for every unit decrease in SO4 there was about a 0.29 decrease in organic aerosol mass (OA = 1.8 × OC). This translated to a 2 μg/m3 decrease in biogenically derived secondary organic aerosol over 15 years in the southeastern United States. The analysis further implied that 35% and 27% in 2001 and 2015, respectively, of average total OA may be biogenically derived secondary organic aerosols and that there was a small but significant decrease in OA not linked to changes in SO4 concentrations. The analysis yields a constraint on ambient SO4-OC relationships that should help to refine and improve regional-scale chemical transport models. [ABSTRACT FROM AUTHOR]