From dust to the sources: The first quantitative assessment of the relative contributions of emissions sources to elements (toxic and non-toxic) in the urban roads of Tehran, Iran

This study represents the first quantitative assessment of the relative contributions of emissions sources to elements in the urban roads of Tehran, Iran. Road dusts (RDs) were collected in the nine districts of Tehran both during the warm and cold seasons (WS and CS) in 2018. Average concentrations of Cr, Cu, Ni, Pb, W, and Zn were remarkably higher in the WS than in the CS. Cu, Pb, and W during the WS and Cd during the CS showed the highest CV (coefficient of divergence). Scanning electron microscopy (SEM) analysis showed complex particle shapes with very irregular structures. Most of them had elongated shapes and contain multiple fine particles attached to the surface. The integrated pollution and risk indices indicated strongly integrated pollution and considerable ecological risk, respectively. The integrated hazard index (Sigma HI) indicated a higher non-carcinogenic risk in children than in adults. However, the integrated carcinogenic risks (Sigma CR) of adults were higher than children. Positive matrix factorization (PMF) model identified five sources of elements including: (1) local soils and geogenic sources (LS + GS) (28.2 %), (2) demolition and construction activities (D + CA) (20.2 %), (3) vehicle exhaust emissions (VEE) (16.2 %), (4) vehicle non-exhaust emissions (VNEE) (18 %), (5) industrial and metallic substances emissions (I + ME) (17.5 %). Among the apportioned sources, the highest Sigma HI was associated with LS + GS, while the lowest Sigma HI was related to VEE. Conversely, VEE contribute the most to the ecological risk (51 %), while LS + GS exhibited the lowest ecological risk contribution (1.25 %). The highest Sigma CR from exposure to RD was associated with I + ME.