Spatio-temporal distribution and source identification of heavy metals in particle size fractions of road dust from a typical industrial district.

Seasonally distribution and source apportionment of Cr, Mn, Ni, Cu, Zn, Cd, and Pb in the road dust (RD) with the four size fraction sizes (<45 μm, 45-63 μm, 63-150 μm and all sizes) in a typical industrial district were investigated using a combination of Moran index, Principal component analysis (PCA), and Positive matrix factorization (PMF). Results showed that from winter to summer, the proportion of the <45 μm fraction dust in the total RD mass increased from 6.72% to 15.92% and that of 63-150 μm dust particles decreased from 31.13% to 21.76%. The proportion of the enrichment factors (EF) at moderate pollution level in winter was higher than that in summer, especially for Cu, Cd and Pb. Further, the heavy metals were relatively enriched in particles 63-150 μm in summer, while in particles <45 μm in winter. Spatially, the distribution of heavy metal concentrations was more concentrated in the winter and showed low levels of regional diffusion. Based on the pollution mapping and PCA-PMF, the integrated source appointment showed that the industrial sources are the main sources of Zn, Cd and Pb, and their contributions are higher at a particle below 45 μm in winter. The construction source significantly influenced Cr, Mn and Cu in summer with little diversity among particle size ranges. Therefore, the <45 μm particles from industrial emission in winter is suggested to be under priority control. And the industrial transformation demonstration area in the Qingshan district should upgrade heavy pollution industry lines and strengthen the monitoring of soot emissions. Further, emissions from coal-fired enterprises should be restricted in winter. Besides, the attention should be paid to avoid urban traffic jams around construction projects and increase enclosed construction ratio.