Characteristics of dust deposited along a transect between central Iran and the Zagros Mountains

Abstract

Abstract Few studies have been reported on the characteristics of dust particles deposited in arid regions of the Middle East. The objective of this study was to identify the variations in physical, chemical, and mineralogical composition of dust particles deposited along an elevational transect lying between central Iran and the Zagros Mountains in the west. Dust samples were collected at 12 localities during September 2008 and July 2009 with and without transboundary dust storms, respectively. Samples were examined for their grain size distribution, and their mineralogical and chemical composition. Surface soils were also sampled from the vicinity of the dust sampling sites and their total elemental compositions were determined. The results indicated that dust deposition rate, mean particle diameter, and concentration of soluble ions in samples from both sampling periods decreased with altitude, with a significantly lower gradient for samples of July 2009 than for those of September 2008. The similarity observed in dust samples taken during September 2008 and those reported by previous studies or measured in local soils and sediments suggests that local soils greatly contribute to the atmospheric dust along the transect in periods with no dust storms. During such periods, dust deposits in the high altitude Zagros Mountains, where annual precipitation is higher and temperature lower, only receive a minor contribution from arid soils of central Iran. However, in July 2009, when a heavy dust storm took place, significant differences were observed between local soils and dust samples along the transect, particularly at high altitudes, in terms of their physicochemical and mineralogical characteristics. These findings, together with satellite images and patterns of wind frequency and direction, clearly indicate the major contribution of a transboundary dust storm, probably originating from Iraqi arid land, to atmospheric deposition in the Zagros area and central Iran. When dust storms blow from across the borders, the contribution of local soils and sediments to aerosols drastically decreases with elevation. If dust storms originating from outside the country continue to occur, not only will they influence the surface soil properties in the Zagros region but will also induce environmental problems in the region.