Ozone photochemistry in an oil and natural gas extraction region during winter: simulations of a snow-free season in the Uintah Basin, Utah P. M. Edwards1,2, C. J. Young1,*, K. Aikin1,2, J. deGouw1,2, W. P. Dubé1,2, F. Geiger3, J. Gilman1,2, D. Helmig4, J. S. Holloway1,2, J. Kercher5, B. Lerner1,2, R. Martin6, R. McLaren7, D. D. Parrish1, J. Peischl1,2, J. M. Roberts1, T. B. Ryerson1, J. Thornton8, C. Warneke1,2, E. J. Williams1, and S. S. Brown1 1NOAA Earth System Research Laboratory, R/CSD7, 325 Broadway, Boulder, CO, USA 2Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA 3Karlsruher Institute für Technologie, IMK-ASF, Karlsruhe, Germany 4Institute of Arctic and Alpine Research, University of Colorado Boulder, Boulder, Colorado, CO, USA 5Chemistry Department, Hiram College, Hiram, Ohio, USA 6Civil and Environmental Engineering Department, Utah State University, UT, USA 7Centre for Atmospheric Chemistry, York University, Toronto, ON, Canada 8Department of Atmospheric Sciences, University of Washington, Seattle, USA *now at: Department of Chemistry, Memorial University of Newfoundland, St. John's, NL Canada
Abstract. The Uintah Basin in northeastern Utah, a region of intense oil and gas
extraction, experienced ozone (O3) concentrations above levels harmful
to human health for multiple 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 process. 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 comprehensive set of observations tests our
understanding of O3 photochemistry in this unusual emissions
environment. A box model, constrained to the observations and using the near-explicit Master Chemical Mechanism (MCM) v3.2 chemistry scheme, has been
used to investigate the sensitivities of O3 production during UBWOS
2012. Simulations identify the O3 production photochemistry to be
highly radical limited (with a radical production rate significantly smaller
than the NOx emission rate). Production of OH from O3 photolysis
(through reaction of O(1D) with water vapor) contributed only 170 pptv day−1,
8% of the total primary radical source on average (primary
radicals being those produced from non-radical precursors). Other radical
sources, including the photolysis of formaldehyde (HCHO, 52%), nitrous
acid (HONO, 26%), and nitryl chloride (ClNO2, 13%) were larger.
O3 production was also found to be highly sensitive to aromatic
volatile organic compound (VOC) concentrations, due to radical amplification
reactions in the oxidation scheme of these species. Radical production was
shown to be small in comparison to the emissions of nitrogen oxides
(NOx), such that NOx acted as the primary radical sink.
Consequently, the system was highly VOC sensitive, despite the much larger
mixing ratio of total non-methane hydrocarbons (230 ppbv (2080 ppbC), 6 week
average) relative to NOx (5.6 ppbv average). However, the importance of
radical sources which are themselves derived from NOx emissions and
chemistry, such as ClNO2 and HONO, make the response of the system to
changes in NOx emissions uncertain. Model simulations attempting to
reproduce conditions expected during snow-covered cold-pool conditions show
a significant increase in O3 production, although calculated
concentrations do not achieve the highest seen during the 2010–2011 O3
pollution events in the Uintah Basin. These box model simulations provide
useful insight into the chemistry controlling winter O3 production in
regions of oil and gas extraction.
Citation: Edwards, P. M., Young, C. J., Aikin, K., deGouw, J., Dubé, W. P., Geiger, F., Gilman, J., Helmig, D., Holloway, J. S., Kercher, J., Lerner, B., Martin, R., McLaren, R., Parrish, D. D., Peischl, J., Roberts, J. M., Ryerson, T. B., Thornton, J., Warneke, C., Williams, E. J., and Brown, S. S.: Ozone photochemistry in an oil and natural gas extraction region during winter: simulations of a snow-free season in the Uintah Basin, Utah, Atmos. Chem. Phys., 13, 8955-8971, doi:10.5194/acp-13-8955-2013, 2013.