Abstract
Abstract. The 2014 Front Range Air Pollution and Photochemistry Éxperiment (FRAPPÉ) aimed to better characterize summertime air quality in the Northern Front Range Metropolitan Area (NFRMA) and its impact on surrounding areas. As part of this study, measurements of gas- and particle-phase species were collected in Rocky Mountain National Park (ROMO), located in the mountains west of the urban northern Front Range corridor from July to October 2014. We report on measurements of ozone from two locations in the park and a suite of volatile organic compounds (VOCs) measured using a continuous real-time gas chromatography (GC) system and a quadrupole proton-transfer-reaction mass spectrometer (PRT-MS) at the ROMO Longs Peak (ROMO-LP) air quality site. We also measured VOCs using canister samples collected along transects connecting the NFRMA and ROMO. These datasets show that ROMO is impacted by NFRMA emission sources, and high observed mixing ratios of VOCs associated with oil and gas extraction (e.g. ethane) and urban sources (e.g. ethene and C2Cl4) occur during periods of upslope transport. Hourly ozone mixing ratios exceeded 70 ppb during six events. Two of the six events were largely associated with VOCs from the oil and gas sector, three high ozone events were associated with a mixture of VOCs from urban and oil and gas sources, and one high ozone event was driven by a stratospheric intrusion. For the high ozone events most associated with emissions from oil and gas activities, we estimate that VOCs and NOx from sources along the Front Range contributed ∼20 ppbv of additional ozone.
Highlights
Ozone (O3) is a regulated pollutant that can impact both human and ecosystem health
Rocky Mountain National Park (ROMO) is a Class I area that is afforded the highest level of air quality protection, while these other locations are in major source regions
We use the background O3 value to estimate the range of influence on O3 production derived from Front Range source by the individual parent alkane precursors. Using this method we can investigate the contribution of other volatile organic compounds (VOCs) to O3 production; in the case where alkanes are the dominant contributor to VOC–OH reactivity, we focus on the alkyl nitrates produced photochemically to provide an estimate of the Northern Front Range Metropolitan Area (NFRMA) on O3
Summary
Mean daytime O3 has been increasing in the Rocky Mountains and throughout much of the west (Strode et al, 2015), and there are concerns about O3 levels and exceedances of the O3 National Ambient Air Quality Standard (NAAQS) at high-elevation sites (Christensen et al, 2015; Musselman and Korfmacher, 2014). In Rocky Mountain National Park (ROMO), a protected Class I area with millions of visitors each year (National Park Service, 2017), O3 mixing ratios often exceed the current NAAQS standard of 70 ppb and vegetation injury thresholds (Kohut et al, 2012). O3 mixing ratios were lower during the summer of 2014 than in the preceding 4 years; the peak O3 mixing ratios were lower and there were fewer hours when mixing ratios exceeded 70 ppb. Weather conditions, including greater rainfall and cloud cover than is typical during the summer months, contributed to lower O3 levels in ROMO
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