ُSaeid Hojati
Abstract
Introduction Khuzestan province in southwestern Iran is one of the most critical areas affected by dust storms due to the arid climate and the abundance of desert areas in its western and southern parts. Dust storms in these areas are among the most critical environmental issues. Air pollution, the development ...
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Introduction Khuzestan province in southwestern Iran is one of the most critical areas affected by dust storms due to the arid climate and the abundance of desert areas in its western and southern parts. Dust storms in these areas are among the most critical environmental issues. Air pollution, the development or increase of respiratory diseases, reduced soil fertility, damage to crops, and reduced solar radiation are among the most critical consequences of dust storms. Dust particles can absorb significant amounts of heavy metals, which facilitate their transport on a large scale due to their fine particle size distribution. Street dust is considered the major source of pollutants from a wide range of traffic, industrial emissions, pesticides, and mining activities. Although many studies have been conducted to identify the origin and pollution status of dust particles in the country, the assessment of pollution and source of street dust particles during dust storms, especially in Ahvaz city, has received less attention. .Thus, this study was conducted to: (1) identify the source of street dust in Ahvaz city, and (2): determine the level of contamination to Pb, Zn, and Cu.Materials and Methods Dust and soil samples were collected respectively at 69 and 23 points from streets and the surface soil (0-5 cm) in Ahvaz city in February 2015. To determine the particle size distribution pattern in the dust samples, they were first dispersed in 1 M sodium hydroxide and 10% sodium hexaphosphate solutions for 2 hours. Then, they were analyzed using A Malvern Hydro 2000g laser diffraction device. The ionic compositions of the dust and soil samples were also determined after extraction from 1 (dust/soil): 5 (water) suspension with an advanced Meterohm 861 model ion chromatography apparatus. The heavy metal contents of soil and dust particles were determined using inductively coupled plasma (ICP) spectroscopy. To determine the Pb, Fe, Cu, and Zn contents, 0.5 g of the dust or soil samples were digested with 60% nitric acid, and after 24 hours, the samples were heated for 0.5 hours at a temperature of 80 ° C. Then, they were filtered with Whatman 42 paper and finally were examined using an Agilent 7000 inductively coupled plasma (ICP) spectrometer. To assess the degree of street dust pollution in Ahvaz city, various indicators, including the single element pollution index and Nemerow integrated pollution index, were calculated. A pollution index is expressed as the ratio of the concentration of an element in soil or dust samples to the same component's baseline value in soil or dust sample. If this index is greater than 1, it indicates different levels of pollution.Results and Discussion The particle size distribution in the studied samples showed a bimodal pattern with more abundance of particles in the size of silt and fine sand. Accordingly, 57 to 89% of the particles were in the silt size, and 5 to 16% were in the size of fine sand. The results also indicated that the abundance of sodium, calcium, chloride, and sulfate ions was comparably higher than the local soils. Similarly, the average concentration of each heavy metal was higher than those of the local soils and the upper earth crust, which followed the order Zn> Cu> Pb. Accordingly, The average Pb, Cu, and Zn concentrations were 5.23, 6.37, and 6.89 times more than their corresponding values in the earth's upper crust. Accordingly, and based on the values obtained from the pollution index (PI), all the studied elements in the street dust of Ahvaz city could be categorized as highly polluted. The average of Nemrow integrated pollution index was found 7.26, which shows a high pollution level for street dust in Ahvaz cityConclusion It seems that dust particles collected from streets and sidewalks of the Ahvaz city are mainly originated from regional focal points in eastern and southeastern parts of the city. When Pb, Cu, and Zn concentrations in the street dust of Ahvaz city and those reported from different cities in Iran and other countries are compared, it is concluded that dust particles deposited over the streets and sidewalks in Ahvaz county have a higher degree of pollution. Therefore, Prompt actions are needed to lower the risk of these elements for the environment.
Soil Physics, Erosion and Conservation
Hossein Kheirabadi; Vahidreza Jalali; Hormozd Naghavi
Abstract
Introduction: The trap efficiency of sediment catcher plays an important role in the study of wind erosion and its measurements. The sediment trap efficiency generally varies with particle size distribution and wind velocity. Worldwide, wind tunnel facility has been used by many researchers to determine ...
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Introduction: The trap efficiency of sediment catcher plays an important role in the study of wind erosion and its measurements. The sediment trap efficiency generally varies with particle size distribution and wind velocity. Worldwide, wind tunnel facility has been used by many researchers to determine the efficiency of sediment samplers designed for the measurement of the deposition of Aeolian dust. Therefore, this study was conducted to investigate the efficiency of BSNE sampler, the transportability of sediment particles per wind velocity, using wind tunnel facility under laboratory conditions. In addition, a new parameter by which sediment transportability can be quantified was introduced. Materials and Methods: The wind tunnel experiments were carried out in an open circulation wind tunnel at the Soil Erosion and Conservation Laboratory, Shahid Bahonar University of Kerman, Iran. The wind tunnel consists of three sections including 1) wind generator section for producing different wind velocities, 2) test area section in which soil sample is placed and 3) sediment collector section. The wind tunnel has a uniform cross section with width and height of 80 cm by 80 cm and a total length of 12 m, with a working section of 7 m in length. The wind velocity can be varied continuously from 1 to 30 m s-1 at 40 cm height equal to 175 km/h at 10 m height. The soil used for the experiments is taken from the surface layer (0-20 cm depth) of a cultivated land from Kerman province (30 14 N and 57 06 E). The soil sample at first was air-dried, thoroughly mixed and then crushed to pass separately through 2, 4.75 and 8 mm sieve sizes in order to prepare three subsamples with different max size of 2 (D2mm), 4.75 (D4.75mm), 8 (D8mm) mm. Experiments were done as factorial based on completely random design with three replications. The factors were the height of sampler, wind velocity and soil aggregate size. Three wind velocities of 6, 10, 14 m s-1 at 40 cm height were introduced over the leveled soil surface with 7 m length and the sediment was collected using BSNE sampler at different heights of 10, 30, 50 and 70 cm at the outlet of the wind tunnel. Also, the total mass of soil loss was measured by differential weighing method for each erosion event. Results and Discussion: Results showed that the sediment flux decreased with increasing height at different wind velocities and was quantified using an exponential function, satisfactorily. The sediment transport rate near soil surface for soils D2mm, D4.75mm and D8mm ranged from 0.28 to 2.11, 0.19 to 1.06 and 0.23 to 0.65 g cm-2 min-1, respectively. This implies the soil having coarser aggregates exhibits less erodibility. Moreover, sediment flux at all heights was increased with increasing wind velocity, whereas it was reduced as soil surface roughness increased. In general, the efficiencies of the BSNE samplers varied from 53.2% to 82.1%, depending on soil aggregate size and wind velocity. The efficiency of BSNE obtained for D2mm, D4.75mm and D8mm, at wind velocity of 6 m s-1 was 61.4, 53.2 and 77.5%, at wind velocity of 10 m s-1 was 56.5, 78.7, 69.5% and at wind velocity of 14 m s-1 was 62.4, 79.1, 82.1%, respectively. Also, the results indicated that the transportability of sediment particles per wind velocity decreased with height, which was described through an exponential function. Overall, the particles in the size range of 125 to 500 micron exhibited the maximum selectivity and frequency in the sediments collected at 10 and 30 cm heights. The finding of this study revealed the high importance of vertical distribution of sediment size particles and their selectivity in wind erosion studies. Conclusion: The finding of this study indicated that most sediment particles were transported near the soil surface, this means that by appropriate conservation practices such as making sufficient roughness through this height, wind erosion can be reduced, significantly. Also, it was found the soils containing coarser aggregates due to higher random roughness show less erodibility and wind erosion rates. Finally, the efficiency of sediment sampler was found to be affected by some other factors, therefore, more attention is needed in the application of these types of samplers while the calibration is of importance, as well.