Uncoupling Aviation and Roadway Contributions to Ultrafine Particle and Black Carbon Exposure in a Marginalized Neighborhood

Ultrafine particles (UFP) and black carbon (BC) are key markers of combustion-related air pollution, yet disentangling their sources remains a challenge in complex urban environments. Using a hybrid mobile and fixed-site monitoring campaign, we investigated a marginalized northwest Toronto neighbourhood downwind of Toronto Pearson International Airport and a freight distribution corridor. Results reveal a divergent spatial footprint for the two pollutants. UFP concentrations correlated strongly with flight activity (r = 0.58, p < 0.05 at 3.5 km), with 1.7- to 3.3-fold enrichment downwind of the airport, measured as the ratio of the IQR of UFP concentrations under downwind versus other wind conditions, reaching 3.2-fold at residential sites ∼8 km away. BC was instead driven by roadway proximity and freight activity, with weak correlations with flight counts. BC–UFP correlations were strong during northerly winds (Mean r = 0.62), but weak downwind of the airport (Mean r = 0.1), indicating shared traffic and industrial sources versus independent sources downwind. Random Forest models (R2 = 0.79 for UFP, R2 = 0.87 for BC) identified industrial land-use and a highway as dominant drivers for both pollutants, airport proximity as a UFP-specific driver, and freight trucking as a BC-specific driver. These findings demonstrate that airport emissions can contribute to increased community UFP exposure several kilometers downwind, while local freight activity drives elevated BC concentrations.