Impacts of Oil and Natural Gas Operations and Urban Emissions on Air Quality in Rocky Mountain National Park during FRAPPÉ

Air Methods, Monitoring and Technology
Oral Presentation

Prepared by B. SIVE1, Y. Zhou2, K. Benedict2, A. Evanoski-Cole2, E. Apel3, R. Hornbrook3, A. Prenni1
1 - National Park Service, Air Resources Division, 7333 W. Jefferson Ave, Lakewood, CO, 80235, United States
2 - Colorado State University, Department of Atmospheric Science, Fort Collins, CO, United States
3 - National Center for Atmospheric Research, Atmospheric Chemistry Observations and Modeling Laboratory, Boulder, CO, United States


Contact Information: barkley_sive@nps.gov; 303-987-6947


ABSTRACT

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. A major upslope event occurred on August 18-19, 2014, where trace gas and ozone levels were significantly elevated at ROMO. The peak hourly ozone value was 74 ppbv while VOCs such as ethane reached approximately 10 ppbv, factors of 2 and 15 above typical background levels. Moreover, the alkyl nitrate to parent hydrocarbon ratios (RONO2/RH) were used to estimate the photochemical age of the air mass transported to the park. The results suggest that air mass age was on the order of 16 hours and points to the photochemical processing of oil and gas emissions as the driving factor for the elevated ozone and trace gas levels observed in the park during this event.