Abstract
We measured the spatial distribution and composition of ozone-forming hydrocarbons, alcohols, and carbonyls in Utah’s Uinta Basin during the winter months of 2019 and 2020. The Uinta Basin contains about 10,000 producing oil and gas wells. Snow cover and the region’s unique topography (i.e., a large basin entirely surrounded by mountains) promote strong, multi-day temperature inversion episodes that concentrate pollution and lead to wintertime ozone production. Indeed, organic compound concentrations were about eight times higher during inversion episodes than during snow-free springtime conditions. We examined spatial associations between wintertime concentrations of organics and oil and gas sources in the region, and we found that concentrations of highly reactive alkenes were higher in areas with dense oil production than in areas with dense gas production. Total alkene+acetylene concentrations were 267 (42, 1146; lower and upper 95% confidence limits) µg m−3 at locations with 340 or more producing oil wells within 10 km (i.e., 75th percentile) versus 12 (9, 23) µg m−3 at locations with 15 or fewer oil wells (i.e., 25th percentile). Twenty-eight percent of the potential for organic compounds to produce ozone was due to alkenes in areas with dense oil production. Spatial correlations and organic compound ratios indicated that the most likely source of excess alkenes in oil-producing areas was natural gas-fueled engines, especially lean-burning (i.e., high air:fuel ratio) artificial lift engines.
Highlights
Utah’s Uinta Basin suffers periodically during winter months from high concentrations of ozone [1,2,3,4], an air pollutant regulated by the Environmental Protection Agency (EPA)
At least part of the reason for underprediction of wintertime ozone is that official inventories appear to underestimate the magnitude of organic compound emissions [1,3] and the percentage of total emissions comprised by reactive organics [11]
Similar to Lyman and Tran, we found that correlations of organic compounds with proximity to oil and gas facilities and related parameters were strongest when summed within a 10 km radius
Summary
The number of exceedance days and concentrations of ozone that occur in a given year are directly related to meteorology, especially persistent snow cover and extended periods of high barometric pressure, which lead to persistent, multi-day thermal inversions that trap pollution and allow ozone to form [5,6]. Three-dimensional photochemical models are generally not able to simulate high wintertime ozone when official emissions inventories are used. At least part of the reason for underprediction of wintertime ozone is that official inventories appear to underestimate the magnitude of organic compound emissions [1,3] and the percentage of total emissions comprised by reactive organics [11]
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