WRF Simulation of a Summer Ozone Event in the Salt Lake Valley Initialized from HRRR Analyses

Poor air quality on the afternoon of 18 June 2015 resulted from lake breeze transport of high ozone concentrations from over the Great Salt Lake into the Salt Lake Valley. An extensive network of near-surface ozone observations were available at this time as a result of the 2015 Great Salt Lake Summer Ozone Study (GSLSO3S). Observations in northern Utah were available from sensors at a dozen state air quality measuring sites, additional fixed locations, vehicles, a light rail car, unmanned aerial vehicles, tethered and free-flying sondes, and a traffic helicopter. Meteorological conditions were monitored from nearly a hundred automated weather stations as well as surface-based remote sensors (ceilometers, sodars, lidar) at several locations.

Simulations of the atmospheric conditions during this day were completed using the WRF model at 1 km horizontal resolution over northern Utah. The model was initialized using hourly analyses at 3 km resolution from the NCEP High Resolution Rapid Refresh (HRRR) model. The HRRR is an operational data assimilation system that uses the WRF model as well. Our effort is the first one to use this state-of-the-art data assimilation system as a means to initialize the WRF for research simulations of an air pollution episode. The results from these model simulations are compared to the HRRR analyses as well as the observations available as part of the GSLSO3S study. The ozone data from the traffic helicopter are of particular interest during this case, as they show high levels of ozone aloft at the lake breeze front boundary. The ability of the WRF model to simulate this narrow boundary is investigated.