Analyzing Wildfire Smoke Impacts on Urban Air Quality Using a Coupled Fire-Atmosphere Model

Wildland fire activity is deteriorating air quality across the Western U.S. Wildland fires emit many pollutants such as fine particulates (PM_2.5) and chemical precursors for ozone (O₃) formation. The chemical formation of O₃ during smoke events is poorly understood as many factors control O₃ production such as the type and amount of fuel being burned, availability of nitrogen oxides and volatile organic compounds. Furthermore, fire-induced winds and smoke shading can affect smoke dispersion and chemical transformations within the smoke plume. For this study, we combined a high-density air quality network located in Salt Lake City (SLC) with model analyses generated by a coupled fire-atmosphere model (WRF-SFIRE-Chem) to explore how wildfire smoke impacts urban air quality. Coupled fire-atmosphere models such as WRF-SFIRE-Chem can explicitly resolve many of the underlying physical and chemical processes that governs smoke transport. This work examines two distinctly different wildfire smoke episodes in SLC where the first episode was associated with smoke that originated from a local wildland fire, while the second smoke episode was likely caused by regional wildland fires. Preliminary results indicate that WRF-SFIRE-Chem was able to skillfully simulate smoke dispersion in terms of the shape and magnitude of the smoke plume when evaluated with our high-density observation network. On average, modeled PM_2.5 concentrations for SLC were 24 μg m^-3 while observed concentrations averaged around 30 μg m^-3. The local smoke event was dominated by small-scale mountain valley circulations, which were captured by our smoke model. For the regional case, WRF-SFIRE-Chem was able to reproduce the large-scale transport of smoke when evaluated with air quality observations across the Western U.S. Interestingly, the large-scale smoke plume exhibited sensitivity to smoke shading effects by altering the location of the highest smoke concentrations by upwards of ~200 km. For this work, we also examined how increased fire activity in the coming decades might offset air quality improvements related to transportation vehicle fleets transitioning to renewable energy sources.