Abstract
Abstract. Nitrogen dioxide (NO2) and total alkyl nitrates (ΣANs) were measured using thermal dissociation laser-induced fluorescence during the 2012 Uintah Basin Winter Ozone Study (UBWOS) in Utah, USA. The observed NO2 concentration was highest before sunrise and lowest in the late afternoon, suggestive of a persistent local source of NO2 coupled with turbulent mixing out of the boundary layer. In contrast, ΣANs co-varied with solar radiation with a noontime maximum, indicating that local photochemical production combined with rapid mixing and/or deposition was the dominant factor in determining the ΣAN concentrations. We calculate that ΣANs were a large fraction (~60%) of the HOx free radical chain termination and show that the temperature dependence of the alkyl nitrate yields enhances the role of ΣANs in local chemistry during winter by comparison to what would occur in the warmer temperatures of summer.
Highlights
The Uintah Basin in Utah is a region of concentrated fossil fuel extraction operations using hydraulic fracturing to extract natural gas and oil from shale formations
The observed ∼ 200 ppb peak ozone in the basin during the winter of 2011 was associated with elevated concentrations of volatile organic compounds (VOCs) coincident with a shallow boundary layer stabilized by snow cover, which doubled as a solar reflector leading to more rapid photochemistry
We further describe the role of organic nitrates in wintertime ozone production and the associated temperature effect by comparing the α values either constrained by observed total alkyl nitrates ( ANs) concentration or derived from temperature-dependent yields from VOC compo
Summary
The Uintah Basin in Utah is a region of concentrated fossil fuel extraction operations using hydraulic fracturing to extract natural gas and oil from shale formations. Organic nitrates (RONO2) are products of atmospheric VOC oxidation in the presence of NOx (NO + NO2) During daytime, their formation involves the association reaction of alkyl peroxy radicals with NO. Field observations have found RONO2 compounds to account for 25 % or more of total reactive nitrogen (NOy, defined as NOx + higher nitrogen oxides). None of these prior field experiments (Farmer et al, 2011; Rosen et al, 2004; Perring et al, 2009, 2010) covered a temperature range wide enough to examine the role of the temperature dependence of α on nitrate formation rates, O3 levels, or OH concentrations
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