Reactive nitrogen partitioning and its relationship to winter ozone events in Utah

R J Wild,W P Dubé,R Mclaren,P R Veres,J M Roberts,J Stutz,T S Bates,C Warneke,J A De Gouw,R C Cohen,L Lee,P M Edwards,B M Lerner,J B Gilman,J S Holloway ,Cora J Young ,A Koss ,J P Kercher ,E J Williams ,Patricia K Quinn ,Kyle J Zarzana ,Bin Yuan ,Joel A Thornton ,Steven S Brown

doi:10.5194/acp-16-573-2016

Abstract

Abstract. High wintertime ozone levels have been observed in the Uintah Basin, Utah, a sparsely populated rural region with intensive oil and gas operations. The reactive nitrogen budget plays an important role in tropospheric ozone formation. Measurements were taken during three field campaigns in the winters of 2012, 2013 and 2014, which experienced varying climatic conditions. Average concentrations of ozone and total reactive nitrogen were observed to be 2.5 times higher in 2013 than 2012, with 2014 an intermediate year in most respects. However, photochemically active NOx (NO + NO2) remained remarkably similar all three years. Nitric acid comprised roughly half of NOz ( ≡ NOy − NOx) in 2013, with nighttime nitric acid formation through heterogeneous uptake of N2O5 contributing approximately 6 times more than daytime formation. In 2012, N2O5 and ClNO2 were larger components of NOz relative to HNO3. The nighttime N2O5 lifetime between the high-ozone year 2013 and the low-ozone year 2012 is lower by a factor of 2.6, and much of this is due to higher aerosol surface area in the high-ozone year of 2013. A box-model simulation supports the importance of nighttime chemistry on the reactive nitrogen budget, showing a large sensitivity of NOx and ozone concentrations to nighttime processes.

Highlights

Wintertime ozone air pollution has recently been observed in several North American basins and currently represents one of the most severe air pollution problems in the United States (Schnell et al, 2009; Carter and Seinfeld, 2012; Helmig et al, 2014; Rappenglück et al, 2014; Oltmans et al, 2014; Edwards et al, 2014)
As with more conventional summertime urban air pollution, winter ozone production requires photochemistry of NOx (= NO + NO2) and volatile organic compounds (VOCs). In polluted areas, such as the Uintah Basin, NOx is emitted mainly from fossil fuel combustion and can further oxidize to form reactive nitrogen species such as HNO3, acyl peroxynitrates (PAN), N2O5, NO3, ClNO2 and organic nitrates, which together with NOx make up total reactive nitrogen (NOy)
The ozone increase is affected by both chemical production and dilution due to the changing boundary layer, chemical ozone production accounts for most of this increase at this site

Summary

Introduction

Wintertime ozone air pollution has recently been observed in several North American basins and currently represents one of the most severe air pollution problems in the United States (Schnell et al, 2009; Carter and Seinfeld, 2012; Helmig et al, 2014; Rappenglück et al, 2014; Oltmans et al, 2014; Edwards et al, 2014). As with more conventional summertime urban air pollution, winter ozone production requires photochemistry of NOx (= NO + NO2) and volatile organic compounds (VOCs) In polluted areas, such as the Uintah Basin, NOx is emitted mainly from fossil fuel combustion and can further oxidize to form reactive nitrogen species such as HNO3, acyl peroxynitrates (PAN), N2O5, NO3, ClNO2 and organic nitrates, which together with NOx make up total reactive nitrogen (NOy). An understanding of the reactive nitrogen budget contributes to understanding ozone formation

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Conclusion