Wildfire Smoke Contributions to Polycyclic Aromatic Hydrocarbon Loadings in Western Canadian Urban Surface Grime.

Wildfires emit large amounts of polycyclic aromatic hydrocarbons (PAHs) into the atmosphere. As PAHs emitted from anthropogenic sources are known to accumulate in urban surface grime present on building exteriors and windows, we hypothesized that PAH-containing wildfire smoke plumes could similarly increase PAH grime loadings. To explore this hypothesis, we coupled analysis of PAHs in grime samples collected from August to November 2021 in two historically smoke-affected Canadian cities, Calgary and Kamloops, with contemporaneous field- and model-based indicators of wildfire influence. In Calgary, a single wildfire smoke day contributed over 20% of total grime PAH loadings during this study's 3-month sampling period, which implies that wildfire inputs have the potential to dominate the grime composition during a typical wildfire season. In Kamloops, although the PAH congener profile displayed a sustained background wildfire influence, total PAH loadings were dominated by a hyper-local combustion event, which highlights that even small-scale urban combustion activities have the potential to control pollutant loadings on nearby surfaces. In both locations, temporal PAH congener profiles showed no evidence of reactive loss, implying that biomass burning contributes to the presence of a persistent PAH reservoir available for direct exposure or runoff-mediated contamination of downstream environmental compartments.