Document Type : مقاله پژوهشی
Dust storm is one of the most important natural phenomena and a kind of severe natural disaster that begins and diffuses under the influence of atmospheric systems. It occurs frequently in desert lands and their surrounding areas in arid and semi-arid regions. The main factors influencing amount of dust in the air are precipitation, vegetation cover, and wind velocity and particle size of soil in source of dust. Over the past decades, Middle East dust storms have caused many problems for the residents of South and South West regions of Iran. Now it is going to change into the main persistent environmental problem in Iran and the Middle East region. The Middle East dust has great impacts on quality of the inhabitant’s lives, visibility and transportation, micro-climate, ecosystem, communication systems and consequent crisis such as, eco – social and environmental problems in the west and south west of Iran. Different aspects of this phenomenon in the Middle East have already been considered by researchers. The aims of this study are to (1) understand the possible source(s) of West of Iran Dust storms and (2) determine the geochemical, mineralogical, trace metals and microbiological characteristics of dust particles in the west of Iran.
2. Study Area
The study area from which sampling was performed, include two provinces of Kermanshah (45.24-48.30 E and 33.36-35.15 N), and Khuzestan (47.42°–50.39° N and 29.58°–32.58°N) which are located close to the Iranian border with Iraq in western Iran. This region comprises 38 cities and a population of more than 6,000,000 people. Topographic elevations in these provinces vary between 0 m (in beaches) and 3701 m (Menar Mountain in Khuzestan province).
Fig. 1. The Study Area
3. Material and Methods
In this study, five severe dust storms in the west and southwest of Iran have been selected. The air sampling was performed in Ahvaz and Mahshar Cities in Khuzestan province, Kermanshah and Qasre-Shirin cities in Kermanshah province. Dust samples were collected to obtain PST by using the high-volume Air (HVA) samplers (Anderson and TCR models) and the fiberglass filters used to get particles. The flow rate of the HVA sampler was 1 M3/min. Also, for some times the sampling was performed by using Low volume Air (LVA) sampler. After the calibration of air sampler, the particles were got from sampling stations, which were located at urban areas in these cities on the height of 2 meter above the ground. The sampler was run continuously for a period of 24 h. Then, the HYSPLIT (HYbrid Single-Particle Lagrangian Integrated Trajectory) model is applied by using a backward trajectory approach in the study periods. The OMI imagery aerosol Index is used to determine the main sources of dust storm. The mineralogy, Sample elemental analyses, toxic trace elements analysis, Microorganisms Analysis of airborne dust samples were analyzed by XRD, XRF, Atomic Absorption and culture-based assays respectively.
4. Results and Discussion
The outputs of HYSPLIT model and aerosol index from OMI imagery show that main sources of DS1 are the area between the west bank of Euphrates and east bank of Tigris in middle of Iraq, deserts lands in south east of Iraq and north east of Arabian Peninsula. In DS2, the main sources of dust are south and southeast of Syrian Desert, an area between Euphrates and Tigris, Nafud desert in north of Arabian Peninsula, and the coastal region in east of Arabian Peninsula. The main sources of dust in DS3 are South of Syrian desert, North of Arabian Peninsula (Nafud desert), middle and south of Iraq. The dust sources in DS4 are Syrian Desert, the area between the west bank of Euphrates and east bank of Tigris, deserts lands in south of Iraq and for DS5 are Syrian Desert, desert lands in west of Iraq, the area between Euphrates and Tigris in middle and south of Iraq. The XRD analysis show that in all samples, quartz, calcite, albeit, muscovite, clinochlore and dolomite are common minerals. But other minerals such as gypsum, orthoclase, actinolite and palygorskite are present in some samples. XRF analyses of dust samples show that chemical compositions are SiO2 (34.82%), CaO (20.48), Al2O3 (8.44%), Fe2O3 (4.36%) and MgO (4.22%). Based on Atomic Absorption analysis, the average concentrations of heavy metals include Zn, Pb, Cd, Cu, Ni and Co are 472.2, 109.2, 10.4, 52.0, 111.2 and 21.0 PPM respectively. Ambient airborne dust microorganisms including the six bacteria species belonging to the genus Bacillus, Staphylococcus, Escherichia coli, Klebsiella, Pseudomonas and Enterobacter were found in dust samples. Also four fungi species isolated were Aspergillus, Rhizopus, mucor and Penicillium, that is common in environment.
The outputs of HYSPLIT model and aerosol index from OMI imagery show that the main sources of airborne dusts for western Iran are dry lake beds and rivers, alluvial deposits and desert lands in Iraq especially the area between the west bank of Euphrates and east bank of Tigris and Hur-Al-Azim lagoon, east, northeast and southeast of Arabian Peninsula, east of Syria and secondary sources of dust storm in the west of Iran with low level quantity are desert land on Africa and Khuzestan province in Iran. The results of XRD analyses show that the main mineral loads are Quartz, Calcite, Gypsum, Albeit, Muscovite, Clinochlore and Dolomite. XRF analyses of dust samples show that the main chemical compositions are SiO2, CaO, Al2O3, Fe2O3 and MgO. Based on Atomic Absorption analysis the mean of heavy metal in dust storm is more than standard level. The microorganism analysis shows that the dust particles are contaminated with bacteria and fungi.