عنوان مقاله [English]
Dusts are referred to as aerosol particles are made up of different sources of land and humanization; they fall on the surface due to their size and density (Salman Zadeh et al., 2012). This phenomenon can damage infrastructures, telecommunications and agricultural products and affect transport through reduced visibility and cause a lot of economic damage (Song et al., 2007, Cao et al., 2016). The purpose of this study is to measure andspatial analysis of the city of Tehran in a one-year statistical period.
Materials and methods
In this research, we used the laboratory method to measure falling dust, collecting dust using Marble Dust Collector. For this purpose, the falling dust was collected using a Marble Dust Collector in 28 stations in Tehran during the statistical period. In order to analyze the spatial distribution of dust and falling dust analysis, we used factors includingthe air quality control company, the number of construction urban under construction in Tehran from Tehran Municipality Organization, mean maximum wind speed parameters, average relative humidity, days of rainfall above 5 mm, the average temperature from the Iran meteorological organization in one-year statistical period (2017) to enter the ArcMap10.5 environment and preparing the desired layers. Statistical analysis of the data showed that the dust distribution have regional (trend) behavior. Therefore, universal trend is better suited. Due to the high preconditions of universal trend in the area with fewer meteorological stations (Chitgar, Geophysics, Mehrabad and Shemiran) is not applicable. Therefore, the IDW method was selected for climatic parameters. Also, the vegetation cover and factories layer were taken to analyze by Euclidean Distance of these complications in GIS for Tehran. Then, all the layers were weighed to determine the weights for using the Reclassify tool. Then, using Expert Choice software, we compared all the layers in pairwise comparison to estimate the value of each layer relative to the other layers. We multiplied the values obtained at each level and transferred all layers to the Fuzzy Overlay tool. The final map of the spatial analysis of falling dust in Tehran city was obtained by using the Gamma 0.9 function. Also, daily speed and wind direction data were received from the Meteorological Organization of the country during the one-year statistical period (30/9/97- 1/10/96). With the help of the WRPLOT software for statistical analysis and the location of the wind, the windrose was drawn.
Results and discussion
The results of computations performed on the data from the collecting of falling dust in Tehran showed that the weights of falling dust in the winter of 2017 is 18943.5 tons, in the spring of 2018 it is equivalent to 27119.5 tons, in the summer of 2018/ it is equivalent to 17111.2 tons and in the fall of 2018 it is equivalent to 23002.3 tons. Also, the results showed that the highest falling dust was collected in spring, autumn, winter and summer, in order of volume. The spatial analysis of Tehran's falling dust is a combination of 9 layers, based on the weight assigned to each. The results showed that the highest amount of dust in the winter of 2017 was found in west Tehran. We had the lowest amount of falling dust in the north and northeast (regions 1 and 4). In the spring, summer and autumn of 2018, the density of the most falling dust was displaced slightly eastward and settled in the southwest. The lowest amount of dusts in these seasons was located in the north and northeast. The halo with the lowest amount of dust falling has expanded further in the autumn than spring and summer.
The results of this study showed that the spatial distribution of falling dust varies in different seasons. Analysis of the results showed that the source of falling dust in the city of Tehran is not uniform throughout the year. Field surveys have showed that the increase in falling dust in different parts of Tehran is directly related to urban construction. In the statistical year of the study, construction and subsequent falling dust has been less in eastern Tehran than that in west. This increase is also associated with pm10. The largest amount of pm10 was reported from the west and southwest, which simultaneously collected the highest amount of falling dust. The highest density of factories and the lowest vegetation density are in these areas. The climatic factors also contributed to these conditions. It was reported that the highest number of rainy days to exceed 5 mm was reported in north and north east of Tehran, where the lowest amount of dust was collected. The highest average temperature in different seasons is reported from Southwest Tehran where it has the highest amount of falling dust in spring, summer and autumn. In winter, climate conditions were slightly different from other seasons. The highest relative humidity reported in other seasons from the West has been reported from north and northeast of this season. The dust collected in winter is higher in the west than that in the southwest. The average maximum wind speed, which is in the west and south, it is in the winter, spring and autumn to the west and southwest. The particles are originating to some extent from Quds, Shahriar, and Malard cities, especially the sand dune areas. They are abandoned in agricultural land in Baharestan, Islam-Shahr and Robat-Karim, and then dust from these areas enters west Tehran. In addition, the wind disperses the dusts generated by construction around the city. In the summer, in addition to the west and southwest, there is wind for north and south east. The northern wind comes from Shemiranat, bringing fresh air to the north and north-east of Tehran. The southeast wind passes from the Pakdasht cement factories in Tehran and also over the abandoned agricultural land of Varamin. The low wind speed in these areas gives more time to hangs off more particles. However, climatic conditions with the lowest relative humidity, the highest temperature, and a lack of rainfall above 5 mm also help to pollute the southern part of Tehran.