Basin Meteorology and High Wintertime Ozone Concentrations in the Uintah Basin in 2013

Wintertime meteorology in the Uintah Basin, Utah, consists mainly of persistent subzero surface temperatures and snow cover, strong surface-based inversions, and weak near-surface winds. Low sun angles and the high albedo of snow, which contribute to the very cold surface temperatures and strong static stability, are seemingly opposite conditions to those typically associated with high ozone (O3) concentrations via photochemical processes—strong insolation and hot temperatures. Yet O3 concentrations as high as 140 ppb (equaling the highest summertime O3 concentrations anywhere else in the U.S. today) are observed from January through early March in the Uintah Basin. Precursor 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. The strong stability inhibits vertical mixing and traps ground-level pollutants within a very shallow layer near the surface. To study the processes leading to high O3, an array of atmospheric chemistry and meteorological measurement systems were deployed to the Uintah Basin during January and February 2013. Here we will discuss the meteorological processes, as revealed by three tethered-balloon ozonesondes systems and NOAA's High Resolution Doppler Lidar (HRDL). Tethered balloon soundings showed that, despite the weakness of the daytime shortwave radiative heating of the snow surface and of the daytime heat fluxes, a shallow unstable mixed layer formed, in which pollutants and potential temperature were often observed to be nearly constant with height. Also often observed was an upslope or upvalley daytime flow by 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.