Source characterization and health risk assessment of community-level air pollutant exposures through a rotating-site trailer in the Puget Sound region

Fixed-site regulatory monitoring and mobile monitoring approaches are each effective in capturing temporal and spatial variations in air pollution, respectively, but limited in addressing both dimensions simultaneously. This study proposed a novel approach using a rotating-site trailer to capture both dimensions for source and health risk apportionment in the Puget Sound region from 2024 to 2025. Multiple air pollutants, including PM 2.5 , BC, NO 2 , CO 2 , and size-resolved particle number concentrations (PNC) were sequentially measured across four overburdened communities identified based on ambient air pollution concentrations, health impacts, and demographics. Positive matrix factorization (PMF) was used to characterize the underlying sources and corresponding health risks for each community separately. A total of five common factors were derived, which were interpreted as fresh transportation emissions (gasoline and aircraft), diesel exhaust, transportation-related urban background, heavy fuels, and aged background mix. This study reveals that transportation-related sources contributed 32-43% of PM 2.5 exposure and corresponding risks and accounted for most of the CO 2 and NO 2 concentrations. In contrast, heavy fuels and aged background mix dominated the PNC of ultrafine particles larger than 42 nm. The findings can lay a foundation for estimating the health benefits of various source control strategies for these overburdened communities in the future.