Ozone photochemistry in an oil and natural gas extraction region during winter: simulations of a snow-free season in the Uintah Basin, Utah

The Uintah Basin in northeastern Utah, a region of intense oil and gas extraction, experienced ozone (O3) con- centrations above levels harmful to human health for multi- ple days during the winters of 2009-2010 and 2010-2011. These wintertime O3 pollution episodes occur during cold, stable periods when the ground is snow-covered, and have been linked to emissions from the oil and gas extraction pro- cess. The Uintah Basin Winter Ozone Study (UBWOS) was a field intensive in early 2012, whose goal was to address current uncertainties in the chemical and physical processes that drive wintertime O3 production in regions of oil and gas development. Although elevated O3 concentrations were not observed during the winter of 2011-2012, the comprehen- sive set of observations tests our understanding of O 3 pho- tochemistry in this unusual emissions environment. A box model, constrained to the observations and using the near- explicit Master Chemical Mechanism (MCM) v3.2 chem- istry scheme, has been used to investigate the sensitivities of O3 production during UBWOS 2012. Simulations iden- tify the O3 production photochemistry to be highly radical limited (with a radical production rate significantly smaller