Geogenic and anthropogenic sources of potentially toxic elements in airborne dust in northeastern Iran

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

Spatial and temporal variations of airborne dust fallout in Khorasan Razavi Province, Northeastern Iran

Dust deposition rates depend mainly on the rate of dust supply, climatic conditions, and topography in the source and sink areas. The objective of this study was to investigate the role of these variables in the spatial and temporal variation of airborne dust fallout in Khorasan Razavi Province, Northeast Iran. Airborne dust samples were collected monthly from May 2014 to April 2015. Dust fallout rate was modelled as a function of air temperature, precipitation, relative humidity, wind velocity and distance from source regions. The lowest and highest rates of atmospheric dust fallout occurred in December and June, with average amounts of 9.97 gm(-2) and 20.96 gm(-2), respectively. The strongest winds were observed in June immediately following a relatively humid period (i.e., March-May) with considerably higher precipitation and lower evaporation. Spatial distributions showed that the highest dust fallout rates occurred in the southern and western parts of the province-areas adjoining the vast playas. During the spring and summer season, the distance from the nearest playa was a key factor that explained more of the variation in dust flux than climatic parameters. Both runoff by fresh sediment moved onto the surface of the playa and the formation of loose sediment on the surfaces of wet playas are mechanisms that can increase dust emissions. The lowest deposition rates were observed in the mountainous region in the north of the province likely due to higher precipitation, atmospheric humidity, and soil moisture. This work represents the first baseline dust data for Khorasan Razavi Province and may be useful in evaluating the effects of future land use and climate change on aeolian land surface processes