VOC Measurements in the Northern Colorado Front Range Metropolitan Area: Investigating the Impact of Oil and Natural Gas Emissions on O3 Production

Abstract:

Authors: Ilana Pollock^1,2, Jake Zaragoza², Emily V. Fischer², Delphine K. Farmer¹

1. Department of Chemistry, Colorado State University, Fort Collins, CO

2. Department of Atmospheric Science, Colorado State University, Fort Collins, CO

During summer months, the Northern Front Range Metropolitan Area (NFRMA) of Colorado consistently violates the 75 ppbv 8-hour EPA National Ambient Air Quality Standard (NAAQS) for ambient ozone (O₃), despite continued reduction in anthropogenic emissions. The region has been deemed an O₃ non-attainment zone since 2008. Ground-level O₃ is produced from photochemical catalytic cycles involving OH radicals, volatile organic compounds (VOCs), and NO_x (NO + NO₂). VOC emissions in the NFRMA are dominated by anthropogenic sources and influenced by biogenic and agricultural sources, while NO_x emissions are mainly from automobile exhaust. A growing concern in the region is the role of oil and natural gas (ONG) on VOC concentrations and the potential for O₃ production. Increases in local VOC emissions will likely cause subsequent increase in local O₃ concentrations as P_O3 increases in a region that is already affected by high O₃episodes.

As a part of the SONGNEX 2015 (Shale Oil and Natural Gas Nexus) campaign, we measured a broad suite of speciated VOCs during two 8-week deployments (March-May 2015, July-September 2015) at the Boulder Atmospheric Observatory in Erie, CO. VOC measurements were made with a custom-online multichannel gas chromatography system (50+ compounds hourly), along with measurements of O₃, SO₂, NO_x, NO_y, PAN, CO, CO₂, and CH₄. We use these data to investigate the role of different VOC sources, and ONG in particular, in contributing to VOC reactivity and thus instantaneous O₃ production. Preliminary analysis of the Spring VOC data indicates that VOC reactivity is dominated by light alkanes typical of ONG emissions - specifically propane, consistent with previous winter-time studies. We will use the observed temperature-dependence of VOC concentrations and reactivity, along with weekday-weekend relationships of O₃ and precursors, to examine the impact of ONG on O₃ production in the Front Range.