Wintertime High-O3 and Local Within-Basin Flows in the Uintah Basin in Eastern Utah

High ozone (O3) concentrations in wintertime have been observed in mountain basins where oil and natural gas drilling and extraction take place. The high concentrations, which may reach 130-140 ppb or more, were observed in conditions of slack winds and persistent snow cover, which climatologically begins with snowfall in December that lasts until spring in more than 90% of winters. One basin, the Uintah Basin in Eastern Utah, was the site of a field program in January-February 2012 to investigate emissions, air chemistry, and meteorological processes producing the high O3. The Uintah Basin had been the site of a measurement campaign in winter of 2010-11, in which the highest O3 was observed at 3 of the nearly 20 surface measurement sites, one (Ouray) in a river bottom, and two others at somewhat elevated sites to the east of the first site. Thus, one issue is the role of meteorological processes (besides snow cover), such as suppressed vertical mixing and horizontal or vertical transport, in the occurrence and spatial distribution of the high O3. Instrumentation deployed to study these effects included tethered-balloon systems, instrumented aircraft, surface sites for chemistry and meteorology measurements, and NOAA's high-resolution Doppler lidar (HRDL). An important question was whether local diurnal slope or basin-wide flows occurred during the low-sun-angle conditions found in the basin in winter.

Winter 2011-12 turned out to be the one in ten or 12 winters having no snow cover. This condition and the occurrence of several days of light gradient winds allowed investigation of the local within-basin flows. The lidar (HRDL), which was located in the eastern sector of the basin, discerned a distinct diurnal pattern in the wind profiles, with low-level easterly flow at night and westerly flow during the day. The daytime flow, if present in normal winters during the high-O3 periods, would explain the occurrence of high O3 at the elevated sites to the east of Ouray. Conditions during this campaign also allowed the emission factor for methane, a major component of the natural gas, from leaks or other fugitive sources, to be estimated. In this presentation we focus on the diurnal pattern of the wind profile, as measured by HRDL, and the spatial variability of the local winds over the basin, as determined by tethered balloon and aircraft wind profiles.