Source apportionment of environmentally persistent free radicals (EPFRs) and heavy metals in size fractions of urban arterial road dust

The partitioning of pollutants in the size-fractions of road dust particles is extremely important to their migration and bioavailability in the air environment. Herein, the pollution characteristics and sources of heavy metals (As, Cd, Cu, Cr, Pb, Zn, Co, Mn, Ni) and environmentally persistent free radicals (EPFRs) are investigated in 64 samples of mixed particle-size road dust in four size fractions (>250 µm, 150–250 µm, 75–150 µm,<75 µm). The samples were collected from urban arterial roads of three cities in the core of Central Plains Urban Agglomeration. The results indicate that 67.70% of the road dust (by mass) consist of the<75 µm particles size fraction, and that the highest levels of EPFRs and heavy metals are concentrated in the<150 µm and< 75 µm size fractions. In addition, Cd exhibits extremely high average enrichment factors (EFs) of 51.84 in the 75–150 µm fraction and 64.80 in the<75 µm fraction. Further analysis reveals a remarkable correlation between EPFR concentration and the concentrations Zn and Cr in the road dust. An application of principal component analysis (PCA) and positive matrix factorization (PMF) to the regional investigation and the layout of functional zones demonstrates that Cr, Pb, Zn and EPFRs are mainly derived from traffic emissions, and account for 51.45–77.86% of the fine particle fraction (<150 µm). Meanwhile, industrial activities are identified as the primary source of Cd and Cu, accounting for 63.07–76.22% of the<150 µm particle size fraction. These findings suggest a potential risk of EPFRs and heavy metals in fine particulate matter, and provide a new insight into the potential sources and health risks of EPFRs in road dust. Therefore, further studies are needed in order to explore the EPFRs in fine particulate particles and to assess their effects upon human health.