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Published April 2012 | Published + Supplemental Material
Journal Article Open

Winter ozone formation and VOC incremental reactivities in the Upper Green River Basin of Wyoming


The Upper Green River Basin (UGRB) in Wyoming experiences ozone episodes in the winter when the air is relatively stagnant and the ground is covered by snow. A modeling study was carried out to assess relative contributions of oxides of nitrogen (NO_x) and individual volatile organic compounds (VOCs), and nitrous acid (HONO) in winter ozone formation episodes in this region. The conditions of two ozone episodes, one in February 2008 and one in March 2011, were represented using a simplified box model with all pollutants present initially, but with the detailed SAPRC-07 chemical mechanism adapted for the temperature and radiation conditions arising from the high surface albedo of the snow that was present. Sensitivity calculations were conducted to assess effects of varying HONO inputs, ambient VOC speciation, and changing treatments of temperature and lighting conditions. The locations modeled were found to be quite different in VOC speciation and sensitivities to VOC and NO_x emissions, with one site modeled for the 2008 episode being highly NO_x-sensitive and insensitive to VOCs and HONO, and the other 2008 site and both 2011 sites being very sensitive to changes in VOC and HONO inputs. Incremental reactivity scales calculated for VOC-sensitive conditions in the UGRB predict far lower relative contributions of alkanes to ozone formation than in the traditional urban-based MIR scale and that the major contributors to ozone formation were the alkenes and the aromatics, despite their relatively small mass contributions. The reactivity scales are affected by the variable ambient VOC speciation and uncertainties in ambient HONO levels. These box model calculations are useful for indicating general sensitivities and reactivity characteristics of these winter UGRB episodes, but fully three-dimensional models will be required to assess ozone abatement strategies in the UGRB.

Additional Information

© 2011 Elsevier Ltd. Open Access article - This article is publicly available. Received 23 September 2011. Revised 9 December 2011. Accepted 9 December 2011. Available online 28 December 2011. This work was funded by Shell Exploration and Production Company. We wish to thank Cara Keslar of the Wyoming Department of Environmental Quality (DEQ) for providing air quality data and for helpful discussions, Dr. Robert Field of the University ofWyoming for making his VOC speciation data available prior to publication, Greg Yarwood and Uarporn Nopmongcol of Environ Corporation for valuable assistance with the scenario inputs, and Roger McClellan and Jim Sewell for helpful discussions. The contents of this report reflect only the opinions and conclusions of the authors, and not necessarily those of Shell Exploration and Production Company, the Wyoming DEQ, or any other individuals or organizations mentioned herein.

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Published - Carter2012p18102Atmos_Environ.pdf

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