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Reactive nitrogen (Nr  =  NO, NO2, HONO) and volatileorganic carbon emissions from oil and gas extraction activities play a majorrole in wintertime ground-level ozone exceedance events of up to 140 ppb inthe Uintah Basin in eastern Utah. Such events occur only when the ground issnow covered, due to the impacts of snow on the stability and depth of theboundary layer and ultraviolet actinic flux at the surface. Recycling ofreactive nitrogen from the photolysis of snow nitrate has been observed inpolar and mid-latitude snow, but snow-sourced reactive nitrogen fluxes inmid-latitude regions have not yet been quantified in the field. Here wepresent vertical profiles of snow nitrate concentration and nitrogen isotopes(δ15N) collected during the Uintah Basin Winter Ozone Study 2014(UBWOS 2014), along with observations of insoluble light-absorbingimpurities, radiation equivalent mean ice grain radii, and snow density thatdetermine snow optical properties. We use the snow optical properties andnitrate concentrations to calculate ultraviolet actinic flux in snow and theproduction of Nr from the photolysis of snow nitrate. The observedδ15N(NO3−) is used to constrain modeled fractional loss ofsnow nitrate in a snow chemistry column model, and thus the source ofNr to the overlying boundary layer. Snow-surface δ15N(NO3−) measurements range from −5 to 10 ‰ andsuggest that the local nitrate burden in the Uintah Basin is dominated byprimary emissions from anthropogenic sources, except during fresh snowfallevents, where remote NOx sources from beyond the basin are dominant.Modeled daily averaged snow-sourced Nr fluxes range from5.6 to 71  ×  107 molec cm−2 s−1 over the course ofthe field campaign, with a maximum noontime value of3.1  ×  109 molec cm−2 s−1. The top-down emissionestimate of primary, anthropogenic NOx in Uintah and Duchesnecounties is at least 300 times higher than the estimated snow NOxemissions presented in this study. Our results suggest that snow-sourcedreactive nitrogen fluxes are minor contributors to the Nr boundarylayer budget in the highly polluted Uintah Basin boundary layer duringwinter 2014

The magnitude of the snow-sourced reactive nitrogen flux to the boundary layer in the Uintah Basin, Utah, USA