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

Abstract

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 PM_2.5, 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. Over 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 PM_2.5 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.