Trace-element concentrations and water-soluble ions in size-segregated dust-borne and soil samples in Sistan, southeast Iran

Abstract

Abstract This study analyzes the chemical composition (water-soluble ions and trace elements) of the total suspended particles (TSP) and particulate matter less than 10 and 2.5 µm (PM10 and PM2.5) in the Sistan basin, southeast Iran during the dusty and windy period June – October 2014. Extreme TSP, PM10 and PM2.5 concentrations, means of 1624.8, 433.4 and 320.8 µgm−3, respectively, were recorded in the Zabol sampling site, while the examined water-soluble ions and trace metals constitute small fractions (∼4.1%–17.7%) of the particulate masses. Intense winds on the dust-storm days result in weathering of soil crust and deflation of evaporate minerals from the dried Hamoun lake beds in the Sistan basin. The soil samples are rich in Ca2+, SO42−, Na+ and Cl− revealing the existence of non-sea salts, as well as in Al, Fe and Mg, while the similarity in the chemical composition between soil and airborne samples indicates that the dust events over Sistan are local in origin. In contrast, low concentrations of secondary ions (i.e., nitrate) and heavy metals (i.e., Pb, Cr, Ni, Cu) indicate less anthropogenic and industrial emissions. Enrichment Factor analysis for TSP, PM10 and PM2.5 reveals that the anthropogenic sources contribute a substantial amount in the heavy metals rather than soil crust, while Al, Fe, Sn, Mg are mostly of crustal origin. The results provide essential knowledge in atmospheric chemistry over Sistan and in establishing mitigation strategies for air pollution control.