Near-road enhancement and solubility of fine and coarse particulate matter trace elements near a major interstate in Detroit, Michigan

Communities near major roadways are disproportionately affected by traffic-related air pollution which can contribute to adverse health outcomes. The specific role of particulate matter (PM) from traffic sources is not fully understood due to complex emissions processes and physical/chemical properties of PM in the near-road environment. To investigate the spatial profile and water solubility of elemental PM species near a major roadway, filter-based measurements of fine (PM2.5) and coarse (PM10-2.5) PM were simultaneously collected at multiple distances (10 m, 100 m, and 300 m) from Interstate I-96 in Detroit, Michigan during September–November 2010. Filters were extracted in water, followed by a hot acid extraction, and analyzed by magnetic sector field high resolution inductively coupled plasma mass spectrometry (HR-ICPMS) to quantify water-soluble and acid-soluble trace elements for each PM size fraction. PM2.5 and PM10-2.5 species measured in the near-road samples included elements associated with traffic activity, local industrial sources, and regional pollution. Metals indicative of brake wear (Ba, Cu) were dramatically enriched near the roadway during downwind conditions (factor of 5 concentration increase), with the largest increase within 100 m of the roadway. Moderate near-roadway increases were observed for crustal elements and other traffic-related PM (Fe, Ca), and the lowest increases observed for regional PM species (S). Water solubility varied by PM species and size, and for PM2.5 included highly (S, K, Ca, Mg, Zn, Ba), moderately (Cu, Mn, Sb, Pb), and minimally (Fe, Ti) water-soluble species, with lower water solubility for most species in PM10-2.5. Results from this study indicate that water-soluble PM2.5 and PM10-2.5 metals, particularly from brake/tire wear, were enhanced in the near-roadway environment which may have human health implications. [Display omitted] •Compared near-road spatial gradients and solubility for PM2.5 and PM10-2.5 elements.•PM2.5 and PM10-2.5 metals were elevated within 100 m of major roadway when downwind.•Traffic, industrial, and regional sources impacted roadside PM2.5 and PM10-2.5•Metals indicative of brake wear (Ba, Cu) had largest increases near roadway.•Water-soluble PM2.5 and PM10-2.5 metals were enhanced in the near-road environment.