Source Attribution Using Volatile Organic Compound Measurements to Assess Air Quality Impacts at Five National Parks in the Western US

Air Methods & Monitoring Part 1
Oral Presentation

Prepared by , A. Prenni, B. Schichtel

Contact Information:; 303-987-6947


A special study was conducted from 13 April through 18 September 2017 at five national parks in the western US to determine the primary sources impacting park air quality, with an emphasis on sites that are approaching or exceeding the National Ambient Air Quality Standard (NAAQS) for ozone. The five national parks sampled were Carlsbad Caverns (CAVE), Grand Canyon (GRCA), Great Basin (GRBA), Joshua Tree (JOTR) and Rocky Mountain (ROMO); at JOTR, samples were collected at two separate sites within the park, Black Rock (JOTR-BR) and Cottonwood Canyon (JOTR-CC). A total of 355 whole air samples were collected at the five parks during the study for volatile organic compound (VOC) measurements. The whole air canister samples were collected every Thursday, Saturday and Monday from 15:00-17:00 local time throughout the study period, with the exception of JOTR-CC, where samples were only collected on Thursdays. The canister samples were analyzed for a comprehensive suite of VOCs, including C2-C10 nonmethane hydrocarbons (NMHCs), C1-C2 halocarbons, C1-C5 alkyl nitrates, oxygenated VOCs, sulfur-containing compounds, nitrogen containing compounds (e.g., acetonitrile and pyrolle), and methane. A signature of elevated NMHC mixing ratios was observed throughout the entire campaign at CAVE. Moreover, the C2-C5 alkane mixing ratios were approximately an order of magnitude greater than regional background levels. Light alkane mixing ratios at CAVE, the most impacted site, were similar to various other sites influenced by oil and gas industry emissions. The i-pentane to n-pentane ratio for CAVE was ~0.86, clearly demonstrating the widespread impact from oil and gas production emissions throughout the region. As a result of the initial findings from CAVE, an intensive sampling campaign was carried out from 8-15 September with a mobile lab equipped with fast response measurements of methane, ethyne, nitrogen oxides, ozone, light scattering and black carbon, in addition to whole air sampling canisters. Mobile sampling was conducted in New Mexico and Texas near CAVE to characterize source areas such as highways and oil and gas sites. An additional 110 whole air samples were collected along the various driving routes that also included Guadalupe Mountains National Park and Salt Creek Wilderness Area for detailed VOC source characterization throughout the region. Results from the CAVE intensive along with the VOC distributions at each park will be presented. The VOC signatures will be used to assess how different sources impact ozone levels and regional air quality for each park unit.