Ozone and Volatile Organic Compound Distributions in Rocky Mountain National Park During FRAPPÉ: Impacts of Oil and Natural Gas Operations and Urban Emissions on Park Air Quality
Monday, 14 December 2015: 11:05
3010 (Moscone West)
The Front Range Air Pollution and Photochemistry Éxperiment (FRAPPÉ) occurred during July and August 2014. This study focused on characterizing and understanding summertime air quality in the Northern Front Range Metropolitan Area (NFRMA), with an emphasis on ozone and its precursors. Exceedances of the National Ambient Air Quality Standard (NAAQS) for ozone occur regularly in the NFRMA during the summertime and impact air quality in Rocky Mountain National Park (ROMO). As part of FRAPPÉ, the National Park Service supplemented its long-term monitoring at its Longs Peak site (~9000 ft.) with enhanced trace gas and aerosol measurements; ozone and meteorological measurements were also deployed at a high altitude site off of Trail Ridge Road (~11,600 ft.). At Longs Peak, a suite of volatile organic compounds (VOCs), including nonmethane hydrocarbons, halocarbons, alkyl nitrates and oxygenated VOCs (OVOCs), were measured using a cryogen-free gas chromatographic system and a proton transfer reaction-mass spectrometer. Additionally, whole air samples were collected along a route from Fort Collins, CO up to Trail Ridge Road several times per week. The transect samples were typically collected during upslope events and aircraft deployment days to characterize air mass composition and to aid in linking the surface and airborne measurements. Ozone distributions from Trail Ridge Road and Longs Peak generally tracked well temporally, with the highest ozone levels measured at the high elevation site; maximum hourly values during FRAPPÉ were 82 ppb and 79 ppb, respectively. A mixed signature containing both urban and oil and gas emissions was regularly observed in air masses encountered in the park, with elevated ozone and VOC levels measured during upslope events. However, the highest levels of alkanes measured at Longs Peak were associated with oil and gas operations, based on the isopentane to n-pentane ratio. Transect samples and aircraft data collected during an upslope event will be used to assess air mass transport to ROMO and will be compared to species concentrations as modeled by the Comprehensive Air quality Model with Extensions (CAMx). CAMx meteorological inputs will be developed using the Weather Research and Forecasting (WRF) model, with special attention paid to accurately capturing upslope flow.