Contributions of resuspended soil and road dust to organic carbon in fine particulate matter in the Midwestern US

Considerable uncertainty still exists regarding the contribution of resuspended soil and road dust to PM2.5 organic carbon (OC) in US urban areas. Contributing factors are the limited knowledge of the OC content of resuspended soils and road dusts, and the variability of the ratio of OC to traditional soil markers such as silicon and aluminum. This study investigates the composition of resuspended soils and road dusts in the Midwestern US, and the contributions of these soils to atmospheric PM2.5 OC. Paved road dust and soil samples were resuspended in a residence chamber from which PM2.5 size fractions were collected and analyzed to generate source profiles. Differences significant to 1 standard deviation were observed in the mass ratios between OC, and silicon and aluminum across different soil types which were larger between soil types within each city (61–97%), than between samples of the same soil type collected in different cities (29–57%). CMB 8.2 source apportionment results revealed large biases in soil apportionments, but these did not greatly affect the overall OC apportionments in six Midwest cities due to the small contributions of soil to total OC (ranging between 0.01 and 0.1 μg m−3). Apportionments of total PM2.5 mass were more greatly affected: biases up to 0.7 μg m−3 for total PM2.5 masses ranging between 7 and 14 μg m−3 were observed when soil profiles were interchanged.