Wildfire-Driven Changes in the Abundance of Gas-Phase Pollutants in the City of Boise, Idaho, during Summer 2018

Wildfire smoke is becoming an increasingly important source of air pollution for the western U.S., and this problem is likely to be exacerbated by climate change. The Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption and Nitrogen (WE-CAN) project deployed the NCAR/NSF C-130 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 Boise, ID boundary layer. We classify ascents and descents with mean HCN > 300 pptv and CH3CN > 200 pptv as smoke-impacted. We contrast data from the 18 smoke-free and 14 smoke-impacted ascents and descents to determine differences between the two data subsets. The smoke was transported from both 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, formaldehyde, and peroxyacetyl nitrate (PAN) were significantly higher than smoke-free 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 abundance of several Hazardous Air Pollutants (HAPs), including benzene formaldehyde, and acetaldehyde, was comparable in magnitude to the annual averages in many major U.S. urban areas.