Abstract

1. Introduction
Dust storm is a natural phenomenon that occurs frequently in the arid and semi-arid regions all over the world (Alijani, 1997). Dust can affect soil fertility, forests, rivers, lakes, and marine ecosystems around the world (McTainsh et al., 2007). Therefore, soil erosion can lead to the loss of the minerals and organic matter of topsoil. Some elements of dust have also an indirect effect on absorption of other elements (Reynolds et al. 2001). It is estimated that each year 2000 Mt dust is emitted into the atmosphere, 75% of which is deposited to the land and 25% to the ocean (Shao et al., 2011). The morphology and elemental composition of the particles can change alone the transportation in reaction to gasses and other particles in the atmosphere (Wang et al., 2007). Identification of the physical properties and chemical composition of dust aerosols is important to determine aerosol sources, mixing processes and transport pathways (Rashki et al., 2013). Chemical analysis of airborne dust can also characterize major and trace elements of airborne dust which is important for quantitative climate modeling, in understanding possible effects on human health, precipitation, ocean biogeochemistry and weathering phenomena (Goudie & Middleton, 2006)

2. Study Area
Shahdad is a region located in west of Lut Desert and South East Kerman province, in centre of Iran. Low precipitation, high temperature, salinity (Alavipanah, 2002) and sever winds are characteristic of this region. Shahdad with a maximum temperature of 71 ° C is one of the hottest regions in the earth (Alavi Panah, 2002, Mildrexler et al., 2006, Ehsani et al., 2008) this region with extensive wind erosion, and intense dust storms, causes adverse effects in regional air quality and human health. To mitigate the impact of these phenomena, it is vital to ascertain the chemical characteristics of airborne and soil dust

3. Material and Methods
This paper examines for the first time, the chemical properties of dust over Shahdad region by collecting dust samples at five stations established at 5 villages close to Lut desert downwind of dust source region, from spring 2013 to September 2013. Furthermore, soil samples were collected from topsoil (0-5 cm depth) at several locations in upwind areas. The data was analyzed to investigate the chemical characteristics of dust, relevance of inferred sources. X-ray Fluorescence (XRF) analysis of airborne and soil dust samples have been produced to show Chemical properties of dust and characterize major and trace elements.

4. Results and Discussion
Major-element and ion-chemistry analyses provide estimates of mineral components, which themselves may be hazardous to human health and ecosystems and can act as carriers of other toxic substances. X-ray Fluorescence (XRF) analyses of all the samples indicate that the most important oxide compositions of the airborne and soil dust are Silicon dioxide (SiO2) in quartz minerals, Calcium oxide (CaO) in calcite minerals and substantial Aluminum oxide (Al2O3) that exhibiting similar percentages for all samples. Chemical analysis of dust samples showed that the main element of dust in the Shahdad is SiO2 (49.35%), which is close to the average of this element in southeastern Iran( 47%) (Rashki et al., 2013) and more than Southwest Iran with (38%) (Zarasvandi et al., 2011). The global average SiO2 is 59.9%. Therefore, amount of Quartz in Iran is lower than Quartz the earth.
Major elements in the dust and soil samples in these analysis are: SiO2 (33.33-55.59%), LOI (12.68-26.31%), CaO (10.12-18.76%), Al2O3 (7.97-10.45%), a small amount of Fe2O3 (3.04-4.34%), Na2O (2.04-13.91%) , MgO (0-3.03%) and K2O (0.85-1.37%), as well as small amounts (