Abstract
High concentrations of ground-level ozone have been observed during wintertime in the Uinta Basin of western Utah, USA, beginning in 2010. We analyze existing ozone and ozone precursor concentration data from 38 sites over 11 winter seasons and conclude that there has been a statistically significant (p < 0.02) decline in ozone concentration over the previous decade. Daily exceedances of the National Ambient Air Quality Standard for ozone (70 ppb) have been trending downward at the rate of nearly four per year. Ozone and NOx concentrations have been trending downward at the rates of about 3 and 0.3 ppb per year, respectively. Concentrations of organics in 2018 were at about 30% of their values in 2012 or 2013. Several markers, annual ozone exceedance counts and median ozone and NOx concentrations, were at their largest values in the period 2010 to 2013 and have never recovered since then. We attribute the decline to (1) weakening global demand for oil and natural gas and (2) more stringent pollution regulations and controls, both of which have occurred over the previous decade. We also see evidence of ozone titration when snow cover is absent.
Highlights
The Basin is one of only two regions worldwide in which winter ozone concentrations consistently above background and consistently above the National Ambient Air Quality Standard (NAAQS) for ozone, 70 ppb, have been observed. (The other is the Upper Green River Basin in western Wyoming, about 300 km to the north.) Winter ozone always occurs in conjunction with persistent, multi-day thermal inversions; an active oil and natural gas extraction industry; and in the presence of a snowpack
Ψ ≈ −15 K/km, and when a snowpack is present, ozone concentrations are above background, depend on proximity to oil and gas wells, and decrease over time
Ψ ≈ −15 K/km, and in the absence of a snowpack, ozone concentrations are below background and appear to be increasing over time
Summary
Received: 17 November 2020 Accepted: 17 December 2020 Published: 23 December 2020. Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Many winters in the Uinta Basin of eastern Utah display high concentrations of ground-level ozone. (The other is the Upper Green River Basin in western Wyoming, about 300 km to the north.) Winter ozone always occurs in conjunction with persistent, multi-day thermal inversions; an active oil and natural gas extraction industry; and in the presence of a snowpack. The industry produces ozone precursors, the inversions trap these precursors within the inversion layer, and the snow surface albedo provides sufficient actinic flux for ozone formation to occur [1,2,3,4,5,6,7,8]
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