Wildfire-driven changes in the abundance of gas-phase pollutants in the city of Boise, ID during summer 2018

During summer 2018, wildfire smoke impacted the atmospheric composition and photochemistry across much of the western U.S. Smoke is becoming an increasingly important source of air pollution for this region, and this problem will continue to be exacerbated by climate change. The Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption and Nitrogen (WE-CAN) project deployed a research aircraft in summer 2018 (22 July – 31 August) to sample wildfire smoke during its first day of atmospheric evolution using Boise, ID as a base. We report on measurements of gas-phase species collected in aircraft ascents and descents through the boundary layer. We classify ascents and descents with mean hydrogen cyanide (HCN) > 300 pptv and acetonitrile (CH₃CN) > 200 pptv as smoke-impacted. We contrast data from the 16 low/no-smoke and 16 smoke-impacted ascents and descents to determine differences between the two data subsets. The smoke was transported from local fires in Idaho as well as from major fire complexes in Oregon and California. During the smoke-impacted periods, the abundances of many gas-phase species, including carbon monoxide (CO), ozone (O₃), formaldehyde (HCHO), and peroxyacetyl nitrate (PAN) were significantly higher than low/no-smoke periods. When compared to ground-based data obtained from the Colorado Front Range in summer 2015, we found that a similar subset of gas-phase species increased when both areas were smoke-impacted. During smoke-impacted periods, the average abundances of several Hazardous Air Pollutants (HAPs), including benzene, HCHO, and acetaldehyde, were comparable in magnitude to the annual averages in many major U.S. urban areas.