نوع مقاله : علمی -پژوهشی
نویسندگان
1 گروه اقلیمشناسی، دانشکده علوم جغرافیایی، دانشگاه خوارزمی، تهران، ایران
2 استادیار دانشگاه تهران
چکیده
کلیدواژهها
عنوان مقاله [English]
نویسندگان [English]
IntroductionHeavy metals are naturally derived from weathering of rocks. However, in cities they are mainly made up of human causes such as industrial activities, urban development, and transportation. The purpose of the present study was to determine the concentration of heavy metals in falling dust of Tehran city, its spatial analysis and to calculate the pollution indices in order to investigate the severity of the impact of external factors (man-made). Materials and MethodsFor this purpose, the dust fallout samples were collected using Marble Dust Collector (MDCO) from 28 different locations across Tehran during the statistical period (2017/12/22- 2018/06/21).To identify and determine the concentration of heavy metals (Cd,Cr,Cu,Ni,Pb,Fe) in the collected dust, XRF analysis was used to determine the spatial and temporal scattering of heavy metals in dust, and the kriging interpolation method was designed for statistical and spatial analysis of wind using the WRPLOT software. With the help of the WRPLOT software the windrose was drawn. Also, the hysplit model was used to trace its route to Tehran metropolis and standard levels (EF) and (Igeo) were used to determine the contamination level of heavy metals.Results and discussionIn winter, pollution caused by heavy elements of cadmium, copper and lead is significantly more at 99% than spring. There was no significant difference between the concentrations of chromium and nickel in winter and spring. In winter, areas in the eastern half of Tehran have the highest concentrations of heavy metals. In spring, the highest concentrations of Cd are in the north of region 5 and 2 and east of region 15. The highest concentration of Cr is in southwestern Tehran. The highest concentrations of Pb and Cu are in the eastern parts of Tehran. Tehran windrose showed that winter and spring had the highest frequency of winds above 8 m / s in west of Tehran. Forward trajectory of dust particles showed that dust particles entered Tehran from sand mines, cement factories and sand processing plants. The enrichment factor (EF) and Geo-accumulation Index (Igeo) concentration of heavy metals in the falling dust in winter 2017 and spring 2018 are (Cd> Pb> Cu> Cr> Ni), respectivelyConclusionMore stable air, inversion of the air and more use of heating appliances in winter increase the concentration of heavy metals in winter than spring. Due to the western-eastern pattern of wind, dust particles that contain heavy metals, are dispersed further east from western Tehran. Due to Tehran's topographic pattern and low wind speed in the east, these elements are more concentrated in the east than in the west. Wind has a huge impact on the pollution and cleanliness of an area from heavy metals. The highest concentration of Cr is in the central areas of south of Tehran. Cr has a different emission source than other heavy metals studied. Cr emission is primarily due to combustion processes, metal industries and cement production. In the spring, Komail West, Hashemi, Hosseinieh Musa al-Reza, 30tir, Shahed 2 stations, were at least +3 standard deviation from the mean Cr. The mentioned stations are located in the southern half of Tehran That's due to the forward trajectory of dust particles in the hysplit. The windrose was drawn in WRPLOT software. One of the reasons of these dusts can be attributed to the sand mines located west of Tehran. In the spring the weather is more unstable. Increased volumes of dust enter these areas and heavy metals stick to the dust particles mostly enter these areas. The results also showed that in winter 2017, Cd in 81.4% and Pb in 85.1% of the studied stations had human origin. In spring 2018, Cd in 64% and Pb in 70.3% of the studied stations had human origin. In both seasons, Cr, Cu and Ni had no human origin at any station.
کلیدواژهها [English]
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