Little attention has been given to the nature and sources of airborne dust affecting northeastern Iran. The objectives of this study were to examine the concentrations of selected potentially toxic elements (i.e., Cr, Cu, Fe,Mn, Ni, Pb, and Zn), distinguish geogenic from anthropogenic sources, and assess the pollution intensity. A total of 600 samples were collected at 50 locations 12 times between May 2014 and April 2015 for fallout rate; 250 of these samples were selected for geochemical analysis. Mean dust concentrations of Cu, Pb, and Zn were found to be higher in autumn compared to spring as well as higher in the most populous cities. Results suggested that Ni, Cr, Mn, and Fe have come from mainly natural geologic sources, while concentrations of Cu, Pb, and Zn in the dust were associated with anthropogenic sources. Enrichment factors showed minimal to significant enrichment for Cu and Pb and moderate to very high enrichment for Cr, Ni, and Zn. The mean geo-accumulation index revealed that the contamination levels for Cu, Pb, and Zn peaked during autumn. In addition to industrial and traffic sources, seasonal differences in meteorological conditions can create frequent and persistent thermal inversions that at ground level can result in increases in Cu, Ni, Pb, and Zn concentrations during autumn.Because of the diversity of geology and terrain in combination with significant seasonal shifts in winds over this region, this study highlights the need to consider both geogenic and anthropogenic sources in evaluating pollution risks in northeastern Iran.

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