Wildfire Smoke beyond PM2.5: Distinct ChemicalMixtures and Hazard Profiles

Despite growing concern about wildfire smoke (WFS) exposure, research has largely focused on fine particle (PM2.5) mass rather than the complex airborne chemical mixtures that may pose distinct health risks. From March to September 2024, passive air samplers in two British Columbia communities collected chemical profiles before, during, and after WFS episodes. Gas chromatography high-resolution mass spectrometry (GC-HRMS) characterized WFS using targeted and nontargeted approaches. Targeted analysis quantified the concentrations of 35 volatile and semivolatile organic compounds (VOCs/SVOCs), while nontargeted analysis (NTA) detected 294 chemicals. Cluster analysis of targeted compounds identified four chemical profiles: two representing site-specific urban background compounds and two enriched with combustion byproducts, including polycyclic aromatic hydrocarbons (PAHs), during episodic WFS. Hierarchical clustering of the NTA chemicals identified mixtures corresponding to distinct hazard profiles of regionally and locally transported WFS from urban background chemical mixtures. Chemical mixtures of regionally transported and locally transported smoke exhibited enrichment patterns of compounds with known developmental, endocrine-disruption, and mutagenic-genotoxic hazards. These findings demonstrate that WFS forms complex, yet reproducible, multipollutant mixtures beyond PM2.5 and emphasize the need to evaluate long-term chemical exposures and their potential contribution to chronic health risks.