Temporal changes in the elemental composition and physicochemical properties of dust from sand sheets of the western Lake Urmia

Sand sheets of the western LU are among the major dust sources in the region. Thus, the aims of the present study were to comprehensive study the dust origins from Sa-sheets; dust characteristics and aerosol temporal variability throughout the dry season. Using dust traps, dust samples were collected during four time periods July, August, October, and November. Soil and dust samples then subjected to physicochemical, mineralogical (XRD), and elemental (ICP-MS) analysis. By means of scanning electron microscopy (SEM), morphology and main chemical constituents of the soil-dust particles were also characterized. Quartz, Calcite, Aragonite and Halite were the dominant minerals in the samples. Elemental analysis results revealed that Calcium (Ca), Magnesium (Mg), Sodium (Na), Silicon (Si), Iron (Fe) and Aluminum (Al) are the dominant constituents of both soil and dust samples. Among rare elements, strontium (88Sr) and barium (Ba) with 3 and 0.21 g kg-1 were the prevailing elements. The calculation of the enrichment factors demonstrated that while dust source 1 (DS1) with higher clay, salt, and silt content contributes more to the dust composition from July to August, dust source 2 (DS2) with less salinity and higher sand content becomes major contributor to dust composition from October to November.  SEM images of the soil samples showed that Aragonite dominated the samples. However, towards the mid dry season and as a consequence of the extensive evaporation, NaCl accumulates in the surface of DS1, resulting in the formation of a thin crust which prevents the soil DS1 from further erosion for the rest of the dry season. Nevertheless, the prevalence of the toxic elements in the dust blown from sand sheets and their transport to the surrounding cities in the direction of the prevailing winds is a serious threat to both human health and agricultural production and thus needs careful attention.