Smoke and the City: Differentiating Aged Wildfire Smoke and Urban PM2.5 Using Integrated Air Quality Measurements

RYAN DURUISSEAU-KUNTZ, Cheol H. Jeong, Christi Jose, Bradley H. Isenor, Greg J. Evans, SOCAAR, University of Toronto

     Abstract Number: 430
     Working Group: Combustion

Abstract
The growing threat of wildfires, fueled by climate change, raises concerns for air quality, health, and climate. Wildfires are a growing source of fine particulate matter (PM2.5), a hazardous pollutant that impacts respiratory, cardiovascular and cognitive health in humans. Wildfire PM2.5 is transported long distances and mixes with urban air pollution, complicating its detection and our understanding of health impacts. The contribution of wildfire smoke to total PM2.5, especially in urban centers, is a research priority which could enhance air quality management and public health protection. As smoke is transported, photochemical reactions induce chemical changes producing PM2.5 with large variations in composition and toxicity. Unravelling how aging affects wildfire PM2.5 composition could indicate its relative toxicity compared to other PM2.5 sources. This research aims to distinguish aged wildfire PM2.5 from the urban background.

During the 2023 wildfire season, data were collected at the Southern Ontario Centre for Atmospheric Aerosol Research (SOCAAR) in Toronto. Measurements from an Aerosol Chemical Speciation Monitor (ACSM) were used to assess changes in aerosol composition. The light absorbing properties of black carbon (BC) during wildfire events supported evaluation of aging extent. An analysis of carbon monoxide (CO) concentrations, ACSM organic aerosol aging tracers, and PM2.5 mass concentrations identified 6 probable wildfire smoke events in 2023. Using the NOAA HYSPLIT model, plume transport times were estimated to range from 13-72+ hours. Molecular tracers m/z 60 (levoglucosan) and m/z 44 (CO2+) aided determination of relative aging during each wildfire event. Events with longer transport times corresponded to decreased m/z 60 and increased m/z 44. The absorption angstrom exponent (AAE) of BC was found to be a predictor of air masses impacted by aged smoke. Decreasing AAE’s were observed downwind of wildfire locations. Variation in PM2.5 composition between wildfire events will also be explored.