Analysis and simulation of a cold-air pool and high wintertime ozone episode in Utah's Uintah Basin

High ozone concentrations associated with a winter cold-air pool during the Uintah Basin Winter Ozone Study are investigated. Field campaign observations combined with numerical simulations are analyzed in Utah's Uintah Basin from 1-6 February 2013 when ozone concentrations exceeded 150 ppb. Cold-air pool sensitivity to cloud microphysics and snow cover variations within the Weather Research and Forecasting model simulations are examined, along with their impact on air quality in Community Multiscale Air Quality model simulations. Ice-dominant clouds are found to enhance cold-air pool strength compared to liquid-dominant clouds through increased nocturnal cooling and decreased longwave cloud forcing. The presence of snow cover also strengthens cold-air pool structure by lowering near-surface air temperatures and increasing boundary layer stability due to reduced absorbed solar insolation by the highalbedo snow surface. Snow cover also increases ozone levels by enhancing solar radiation available for photochemical reactions. Flow features affecting Uintah Basin cold-air pools that affect pollutant mixing and air quality within the basin are studied, including: penetration of clean air into the basin from across the surrounding mountains, elevated easterlies within the inversion layer, and diurnal upslope and drainage flows.