Meteorological and Topographic Conditions in the Wintertime Uintah Basin Leading to High Ozone Concentrations

High concentrations of O3 in the Uintah Basin, Utah, during winter have been observed during periods of snow cover in the basin. Low sun angles and the high albedo of snow contribute to very cold surface temperatures and strong static stability, which inhibit vertical mixing and trap pollutants within a very shallow layer near the ground. The pollutants are emitted from a variety of sources related to petroleum extraction in the western part of the basin and natural gas ';fracking' and extraction in the eastern half. These unevenly distributed sources also include several point and area NOX sources distributed around the basin as well. Despite the weakness of the daytime shortwave radiative heating of the snow surface and the daytime heat fluxes, a shallow unstable mixed layer is observed to form, in which pollutants and potential temperature are often observed to be nearly constant with height. Also often observed is an upslope or upvalley daytime flow by NOAA's High Resolution Doppler Lidar (HRDL), which was located in the eastern portion of the basin. At this location, the weak (1-3 m/s) upslope flow was from a westerly direction during daytime. At night, a shallow, weak (1-3 m/s) easterly drainage flow was routinely observed by the lidar. The sloshing of air by the alternating daytime and nighttime flows, along with other weak oscillatory flows in the basin cold pool, had the effect of mingling the pollutants from the various sources, which may have contributed to the highest O3 concentrations.