Urban-Rural PM2.5 Dynamics in Saskatchewan: Wildfire Amplification Effects

Saskatchewan's prairie cities occupy a climatic and geographic frontier rarely examined in Canadian aerosol research, characterised by cold winters with strong thermal inversions, photochemically active summers, and increasing exposure to wildfire smoke. While Canadian observational studies have largely focused on dense metropolitan corridors (e.g., Montreal, Toronto and Vancouver), the distinct emission regimes, meteorological extremes, and wildfire exposure of Prairie provinces remain poorly characterized. In this study, we use a decade of continuous monitoring data from the National Air Pollution Surveillance (NAPS) network across six urban centers and remote background sites in Saskatchewan to investigate spatiotemporal dynamics of PM2.5, O3, NOX, and CO, and to quantify the extent to which wildfire amplification is reshaping the provincial air quality trajectory.

Seasonal decomposition reveals that winter inversions systematically elevate primary pollutants in urban cores beyond what emission inventories alone predict, while wildfire smoke events increasingly dominate summer (June–August) and fall PM2.5 (September–October) loading at both urban and rural sites. Summer daily mean PM2.5 ranged from 11.02 μg m-3 (Estevan) to 13.64 μg m-3 (Saskatoon) approximately 1.5 to 2.1 times higher than winter (November–March) means, with 98th percentile daily concentrations exceeding the Canadian Ambient Air Quality Standards (CAAQS) of 27 μg m-3 (24-hour) at every site and peaking at 98.24 µg m⁻³ at Buffalo Narrows. Critically, statistical trend analysis demonstrates that smoke-driven exceedances are now offsetting multi-decadal gains from emission controls, with implications for how the CAAQS design values are applied in fire-prone cold-climate regions.

These findings have important implications for the application of CAAQS design values in fire-prone, cold-climate regions. This study provides the first comprehensive, multi-pollutant, multi-site trend analysis for Saskatchewan and offers a transferable framework for other under-monitored Prairie and cold-climate jurisdictions navigating the intersection of climate change, wildfire, and air quality regulation.