Most assessments of road dust have focused largely on the resuspension of materials from the paved road while the contribution from unpaved shoulder to particulate matter is poorly understood. We evaluated the role of unpaved road shoulders in the contribution of particulate matter emitted by analyzing elements in the road dust. We collected road dust samples and employed US-EPA empirical equations. The results of TSP emission reveal that unpaved shoulder adjacent to paved roads (43.1–29.9%) is a potential emitter than that at roundabouts (27%). In paved road environment, the contribution of TSP emission was 54.9–25.6% from unpaved shoulders based on driving share of vehicles. TSP emission results suggest that waste material is frequently exchanged from paved to unpaved shoulder, which leads to seasonal variations in paved road. The observed particle size of paved surface waste material shows that about 36% particles were less than 2.5 μm and 52% were greater than 10 μm, suggesting that dust is resuspendable and presents a health risk due to being respirable. Elemental analysis confirmed the presence of the toxic elements Cr, Ni, Cu, Zn, Pb, Sn, Sb, and Ba in waste material. Moreover, receptor models indicate that the waste material comprised of elements from tire wear (31%), mineral dust (27%), brake wear (17%), vehicle exhaust (14%), and coal (7%). The elemental contribution of coal is a location-specific source identified from principal component analysis and hierarchical cluster analysis, which originated spillage during transportation. The study illustrates the contributions of PM emission from the different road networks and the mechanism of exchange of waste materials.

Graphical Abstract

Microscopic observation of resuspension and transportation of road dust due to vehicular movement leads to advection mechanism at the roundabout and the paved road having unpaved shoulders.