The Impact of Aged Canadian Wildfire Smoke on Measurements of Organic Aerosol Particles over Chicago, Detroit, Toronto, and New York City during the 2023 Atmospheric Emissions and Reactions Observed from Megacities to Marine Areas (AEROMMA) Study

Organic aerosol particles are a dominant constituent of PM2.5 (particulate matter with diameters less than 2.5 micrometers), with major sources from biogenic, urban regions, and biomass burning. During the summer of 2023, the United States was periodically affected by the presence of heavy wildfire smoke originating from Canada. Some of these smoke plumes were present in the air above Chicago, Detroit, Toronto, and New York City during the NOAA Atmospheric Emissions and Reactions Observed from Megacities to Marine Areas (AEROMMA) field campaign. Here we present aircraft measurements of particles and gases to examine the impact of wildfire smoke on these cities and determine the sources of organic aerosols from gas-phase tracer relationships of species. Our research focuses on acetonitrile, a marker for biomass burning, decamethylcyclopentasiloxane (D5-siloxane), a marker for urban volatile chemical products, and levoglucosan, a primary marker of biomass burning. In some cases, there is a clear difference in the relationship between organic aerosol mass concentration and carbon monoxide mixing ratios depending on the presence of the two gas-phase tracers acetonitrile vs D5-siloxane. In contrast, levoglucosan decreases in intensity as biomass burning aerosols age and was close to background levels in the smoke plumes sampled during AEROMMA. We will further examine the aerosol mass spectra for additional ions identifying the relatively-fresh urban or aged biomass burning sources.