RAPID: Chemistry and Vertical Transport of Hox Radical Precursors During the Uintah Basin Winter Ozone Study in Utah

University Of California-Los Angeles, Los Angeles CA

Investigators

Abstract

Wintertime ozone pollution in sparsely populated rural areas that have come under the influence of nitrogen oxide and volatile organic compound emissions from hydraulic fracturing natural gas drilling activities is a relatively recent phenomenon. The fact that ozone mixing ratios exceed the federal air quality standard in winter but not in summer poses a scientific puzzle. Weak solar irradiance in mid-winter is expected to lead to a considerable slowdown of photochemistry and consequently low ozone levels. It has been hypothesized that specific environmental conditions, in particular the presence of surface snow, are an important factor in the formation of wintertime ozone. Snow increases surface albedo and, thus, enhances the actinic flux in winter to levels more similar to those in the tropics. However, it appears that this effect only explains part of the high wintertime ozone levels. It has also been hypothesized that snow chemistry can be an efficient source of the hydroxyl and hydroperoxyl (OH + HO2 = HOx) radical precursors nitrous acid (HONO) and formaldehyde (HCHO). Elevated levels of these species could further accelerate the formation of ozone in winter. The weak wintertime solar irradiance and high infrared emissivity of snow also lead to the formation of strong and shallow surface inversions, which can further accelerate ozone formation by concentrating pollutants near the surface. The Uintah Basin Winter Ozone Study jointly organized by NOAA/ESRL Chemical Sciences Division, Physical Sciences Division, NOAA Pacific Marine Environmental Laboratory, and the University of Colorado (http://www.esrl.noaa.gov/csd/tropchem/2012ubwos/) field experiment is planned for the time period of January 15 to March 1, 2012. The measurements to be performed offer a unique opportunity to study polluted wintertime atmospheric chemistry of ozone, as a large number of complementary measurements will be performed by other investigators. The following scientific hypotheses related to wintertime ozone formation will be tested: - The photolysis of HONO, and to a lesser extent HCHO, are important, if not the dominant primary HOX formation pathways under wintertime conditions. - Chemistry in the snow or on the snow-covered ground strongly contributes to the mixing ratios of HONO and HCHO, and is thus an important factor for HOX and ozone formation. - Surface inversions and suppressed vertical mixing play a crucial role in concentrating pollutants in a shallow surface layer, thus accelerating surface ozone formation. Vertical profile measurements of ozone, nitrogen dioxide, HONO and HCHO will be obtained by Long-Path Differential Optical Absorption Spectrometery. The acquired data, together with data available from other investigators, will be interpreted using established methods. Activities will be closely coordinated with the Utah Department of Environmental Quality and the U.S. Environmental Protection Agency, Region 8. The results will thus directly be used to develop mitigation strategies for the ozone pollution found in the Uintah Basin and thus benefit the local population. The results will also benefit other locations with similar problems, such as the Upper Green River Basin, Wyoming. The current expansion of natural gas drilling activities also makes this a timely proposal as the air quality problem found in Utah and Wyoming may soon also occur in other places in the U.S. and Canada. The project will also provide a graduate student a career development opportunity, building on previous experience performing measurements and analyzing trace gas vertical profile data.