Assessment of geochemical and sedimentological characteristics of atmospheric dust in Shiraz, southwest Iran

• Main Authors: Amir Karimian Torghabeh, Biswajeet Pradhan, Ashkan Jahandari
• Format: Article
• Language: English
• Published: Elsevier 2020-05-01
• Series: Geoscience Frontiers
• Online Access: http://www.sciencedirect.com/science/article/pii/S1674987119301628

Geogenic dust is commonly believed to be one of the most important environmental problems in the Middle East. The present study investigated the geochemical characteristics of atmospheric dust particles in Shiraz City (south of Iran). Atmospheric dust samples were collected through a dry collector method by using glass trays at 10 location sites in May 2018. Elemental composition was analysed through inductively coupled plasma optical emission spectrometry. Meteorological data showed that the dustiest days were usually in spring and summer, particularly in April. X-ray diffraction analysis of atmospheric dust samples indicated that the mineralogical composition of atmospheric dust was calcite ​+ ​dolomite (24%)>palygorskite (18%)>quartz (14%)>muscovite (13%)>albite (11%)>kaolinite (7%)>gypsum (7%)>zircon ​= ​anatase (3%). The high occurrence of palygorskite (16%–23%) could serve as a tracer of the source areas of dust storms from the desert of Iraq and Saudi Arabia to the South of Iran. Scanning electron microscopy indicated that the sizes of the collected dust varied from 50 ​μm to 0.8 ​μm, but 10 ​μm was the predominant size. The atmospheric dust collected had prismatic trigonal–rhombohedral crystals and semi-rounded irregular shapes. Moreover, diatoms were detected in several samples, suggesting that emissions from dry-bed lakes, such as Hoor Al-Azim Wetland (located in the southwest of Iran), also contributed to the dust load. Backward trajectory simulations were performed at the date of sampling by using the NOAA HYSPLIT model. Results showed that the sources of atmospheric dust in the study area were the eastern area of Iraq, eastern desert of Saudi Arabia, Kuwait and Khuzestan Province. The Ca/Al ratio of the collected samples (1.14) was different from the upper continental crust (UCC) value (UCC ​= ​0.37), whereas Mg/Al (0.29), K/Al (0.22) and Ti/Al (0.07) ratios were close to the UCC value (0.04). This condition favours desert calcisols as the main mineral dust sources. Analysis of the crustal enrichment factor (EFcrustal) revealed geogenic sources for V, Mo, Pb, Sr, Cu and Zn (<2), whereas anthropogenic sources affected As, Cd, Cr and Ni. Keywords: Dust storm, Atmospheric dust, Heavy metals, Diatom, Palygorskite, Provenance