Reactive Nitrogen Partitioning and its Relationship to Winter Ozone Events in Utah

Recent air quality measurements have shown anomalously large concentrations of wintertime ozone in Utah's Uintah Basin, host to intensive oil and gas operations. As part of the Uintah Basin Winter Ozone Studies (UBWOS) in January-February of 2012 and 2013, a variety of instruments were deployed to measure speciated reactive nitrogen and ozone. Here we present an analysis and comparison of reactive nitrogen data for the two years. We also describe a recently developed measurement of total reactive nitrogen (NO_y) by cavity ring-down spectroscopy, which was deployed for the first time in 2013. Compared to 2012, which had very different meteorological conditions, ozone production rates in 2013 were roughly three times faster, leading to numerous and substantial exceedances of national air quality standards. Furthermore, despite considerably higher NO_y levels in 2013 compared to 2012, levels of photochemically active NO_x was remarkably similar between the two years. Much of the reactive nitrogen oxidation occurred at night, suggesting that nighttime processes played an important role in defining the conditions for daytime photochemistry. Our findings regarding the reactive nitrogen budget help us understand the role different NO_x oxidation processes in O₃ photochemistry, as well as the overall sensitivity of O₃ production to nitrogen oxides in this environment.