Seminar

Abstract

Ozone is the primary component of photochemical smog and, until recently, was considered to be a summer time air pollutant. Low solar zenith angles and cold temperatures in the winter slow the rate of the photochemical reactions of VOC and NOx that form ozone. Unexpectedly, elevated winter ozone levels exceeding EPA's 8-hour average ambient air quality standard of 75 ppb were observed in the Upper Green River Basin in WY beginning in 2005. More recently, winter ozone 8-hour averages exceeding 100 ppb were observed in Utah's Uintah Basin in 2010 and 2011. Schnell et al (2009) demonstrated that the WY winter ozone episodes were not a result of stratospheric ozone intrusions and that in situ photochemical production was the most likely cause. Schnell et al also identified the combination of a strong, shallow inversion layer, VOC and NOx emissions from oil and gas production, and the effect of snow cover on enhanced albedo and increased photolysis rates as key factors responsible for winter ozone formation. The WY DEQ carried out ambient monitoring studies each year from 2007 through 2011 to understand the processes responsible for winter ozone formation and its sensitivity to VOC and NOx. The WY DEQ's research studies were hampered by low winter ozone levels in 2007, 2009 and 2010. However, high winter ozone concentrations were observed in 2008 and 2011 and the WY DEQ (WDEQ 2008, 2010, 2011) identified several factors that promote winter ozone formation including very high ratios of VOC/NOx, on the order of 100:1, elevated concentrations of high reactivity VOC and elevated day time HONO concentrations. Significant uncertainties remain in the factors that affect winter ozone formation and its sensitivity to VOC and NOx, including the sources of HONO and sources of some highly reactive VOC species and in the mixing and transport of NOx plumes emitted from compressor stations and drill rigs. In the Uintah Basin, Utah State University and the Energy Dynamics Lab carried out a distributed monitoring study in 2011 (Martin et al, 2011). Although there were limited measurements of VOC and NOx precursors in the 2011 study, the ozone and meteorology data show the same types of conditions associated with winter ozone in UT as observed in WY. A more extensive field study is planned for the Uintah Basin in winter 2012, building on the lessons learned from the previous WY DEQ studies and the 2011 Uintah Basin study. The 2012 Uintah Basin study includes researchers from NOAA, Utah State University and Energy Dynamics Lab (EDL), Utah Department of Air Quality, University of Colorado and others. Nearly $3 million in funding is being provided by the Western Energy Alliance, the Uintah Impact Mitigation Special Service District (UIMSSD), BLM and EPA, with significant contributions of internal funding from NOAA, UIMSSD, EDL, and Utah DEQ. Specific objectives include more comprehensive measurements of ozone precursors and radical sources to characterize more accurately the sensitivity of ozone to VOC and NOx; distributed and mobile measurements of VOC and NOx to support development of improved emissions inventories, and vertical profile measurements to characterize the height of the inversion layer and vertical mixing of VOC and NOx.

References

Schnell, R.C., S.J. Oltmans, R.R. Neely, M.S. Endres, J.V. Molenar, A. B. White, (2009) Rapid photochemical production of ozone at high concentrations in a rural site during winter, Nature Geosci. 2, 120-122.

WDEQ (2008) Final Report, 2011 Upper Green River Winter Ozone Study, prepared by ENVIRON International Corporation, Meteorological Solutions Inc. and T & B Systems (2008) Submitted to: Wyoming DEQ - Air Quality Division, Herschler Building, 122 West 25th Street, Cheyenne, Wyoming 82002

WDEQ (2010) Final Report, 2010 Upper Green River Ozone Study prepared by Meteorological Solutions Inc., ENVIRON International Corporation and T & B Systems, Submitted to: Wyoming DEQ - Air Quality Division, Herschler Building, 122 West 25th Street, Cheyenne, Wyoming 82002

WDEQ (2011) Final Report, 2011 Upper Green River Ozone Study prepared by Meteorological Solutions Inc., ENVIRON International Corporation and T & B Systems, Submitted to: Wyoming DEQ - Air Quality Division, Herschler Building, 122 West 25th Street, Cheyenne, Wyoming 82002

Martin, R., K. Moore, M. Mansfield, S. Hill, K. Harper, H. Shorthill (2011) Final Report: Uinta Basin Winter Ozone and Air Quality Study December 2010 - March 2011, Energy Dynamics Laboratory, Utah State University Research Foundation (USURF), Submitted To: Uintah Impact Mitigation Special Service District, 320 North Aggie Boulevard, Vernal, Utah 84078