The Impact of the 2023 Canadian Forest Fires on Air Quality in Southern Ontario

The record-breaking 2023 Canadian wildfire season had large-scale burning that resulted in wide-reaching long-range transport of smoke plumes and their associated trace gases. This paper examines three events (May 16-23, June 3-9 and June 17-30, 2023) during which the composition of smoke was measured over Toronto and Egbert, Ontario. Tropospheric columns (0–10 km) of CO, C2H6, CH3OH, HCN, HCOOH, NH3 and O3 were measured using high-resolution Fourier transform infrared spectrometers. Coincident enhancements of CO and other gases during the events were used to calculate enhancement ratios. Correlations with CO were observed for C2H6, CH3OH, HCN and HCOOH, but not for NH3 and O3. Plume transport was investigated with the Hybrid Single-Particle Lagrangian Integrated Trajectory model, the GEM-MACH-FireWork (GM-FW) air quality model, and Measurements of Pollution in the Troposphere (MOPITT) CO satellite data. Additional measurements examined were surface CO, O3, and PM2.5, plume height from a Mini Micro Pulse Lidar, and EM27/SUN XCO columns. GM-FW model output was compared with ground-based surface and 0–10 km column measurements, and MOPITT CO maps. ... mehrOver the 2023 forest fire season (May-September), the model underestimated background tropospheric columns of CO, NH3 and O3, but generally overestimated enhancements during smoke events. Relative to surface in situ measurements, GM-FW seasonal averages overestimated CO and underestimated O3 (which was not generally enhanced during smoke events), while PM2.5 fluctuated between a positive and negative bias. Compared to MOPITT, the GM-FW event-averaged CO columns appropriately represent plume dispersion across the country, with some offsets on the scale of the ground-based locations that are consistent with the discussed findings.