year 13, Issue 1 (Spring 2023 2023)
E.E.R. 2023, 13(1): 155-174 |
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Serati N, Saffari A, Ghohrodi tali M, Alinoori K. A Comparative Study of Changes in the Spatial Pattern of Dust in Tehran Province in the 2000-2019 Period. E.E.R. 2023; 13 (1) :155-174
URL: http://magazine.hormozgan.ac.ir/article-1-714-en.html
URL: http://magazine.hormozgan.ac.ir/article-1-714-en.html
Department of Natural Geography, Faculty of Geographical Sciences, Kharazmi University, Tehran, Iran , saffari@khu.ac.ir
Abstract: (1757 Views)
1- Introduction
Dust is a sign of environmental erosion and in arid lands can be caused by various factors: climate change in the region such as lack of rainfall, the presence of erodible soil particles and high wind speeds are good conditions for the occurrence and severity of storms. The abundance of dust particles in the atmosphere, in addition to the intensity and speed of the wind and the dryness of the particles, also depends on the size and diameter of the particles. To better understand the effects of dust, and its origin, and to control and provide a response to its harmful effects, it is necessary to regularly identify and monitor this phenomenon. Today, remote sensing technology is widely used in studies on aerosols and dust particles. MODIS sensor images from Terra and Aqua satellites are commonly used in such studies due to their extensive coverage, high data acquisition frequency, and their 36 spectral bands. This research has been carried out with the aim of performing a comparative study of changes in the spatial pattern of fine dust phenomenon in Tehran province during 20 years (2000-2019 time period).
2- Methodology
After examining the days with dust phenomenon in Tehran province, and extracting the Wind rose diagrams related to these days by using the MODIS sensor images on the days with dust phenomenon in the desired time period, three main indicators related to dust including NDDI index (Normalized Dust Difference), AOD index (Aerosol Optical Depth) and DBAAEL index (Deep Blue Aerosol Angstrom Exponent Land) were calculated.
Statistical data related to the index "The number of reports associated with the phenomenon of dust in the synoptic stations of Tehran province in the period of 2000 to 2019" has been used to prepare the province's flowchart. Also, the MYDO2HKM 250, 500 m product level 1 images of the Modis sensor of Terra and Aqua satellites in the same time period and on the days with recorded dust phenomenon were used to study the NDDI index (normalized dust ratio). The NDDI index is expressed with the following relation:
NDDI = (NIR-R) / (NIR + R) = (b1-b2) / (b1 + b2)
Aerosol Optical Depth (AOD) is a measure of the attenuation of the input radiation to the atmosphere due to the absorption and scattering of suspended particles in the vertical column. This index has a certain range from 0 to 0.5 and its range increases in proportion to the increase in dust. To obtain this index, the MODO4-L.A product has used level 1 images of the Modis sensor of Terra and Aqua satellites in the specified time period and dusty days.
Another indicator that can be used to obtain particle size is DBAAEL Index. In this index, the particle size smaller than 1 and with a rough and burly condition are considered as dust. However, if the particle size is larger than 1, the particles are finer in texture and include smoke and dust. In addition, the DBAAEL index from MODO4-L.A product Modis sensor images with 10 by 10 spatial resolution have been extracted.
3- Results
Combining all NDDI index patterns in 2000 indicates that some areas of Iraq, a large part of the western slopes of the Zagros, the central desert of Iran and the northern slopes of the Binalood-Aladagh range have the highest dust density in Iran. Dust density center is observed in the eastern parts of Tehran province too. However, this pattern has changed a lot after 20 years and in 2019, it is clearly less than what has already been estimated. The most important and dense dust particles in the vertical column of the atmosphere in 2000 can be seen in the eastern border of Iran from north to south, Khuzestan plain and southwestern and southern plains of Tehran province (hills, cut plateaus and badlands) and northern Iraq. The density center is located outside the province (south of theVaramin plain).
The general pattern of the AOD index in 2019 is concentrated in the northern part of Iraqi Kurdistan and the Mesopotamian region in the south of the country, as well as in the desert of central Iran stretched to the east. Although one center can be seen in Varamin plain within the borders of Tehran province, no other significant density center is observed within the borders of the province.
The highest density of coarse particles in 2000 can be seen on the central desert of Iran and Loot desert and deserts of western Iraq, and in this year the entire southern part of Tehran province from west to east has been involved in coarse particles. But in general, particle density in 2019 has decreased throughout Iran. And the compact center of most particles is limited to the central deserts of Iran and southern Iraq. The western plains and then the southern plains of Tehran province had the highest volume and thickness of dust particles in 2019, respectively.
4- Discussion & Conclusions
In summarizing the dust patterns in 2000, most of the dust center density centers were located in northern Iraq, the plains in the south of Lake Urmia and the plains on the western slopes of the Zagros Mountain Range. However, the final maps extracted from the 2019 patterns showed the presence of dust center in the southern latitude of Tehran province from Shahriyar to Varamin and specifically on the sedimentary landforms at the end of the catchments of Tehran province. In northwestern Iran, in the area between the Zarrineh and Simineh rivers in the south of Lake Urmia, the effect of lowering the lake water level and land drying is clearly seen in the dust density patterns. The next large and concentrated area is the area between the provinces of West Azerbaijan, Zanjan and Kurdistan; although this area is part of the dense Zagros Mountains, it has created a good place to concentrate dust. In 2019, however, the whole pattern changes significantly, and the coarse particles are concentrated in the south of Tehran. In general, the level of Varamin and Robat Karim counties is the focus of the dust pattern in the study area.
Keywords: AOD (Aerosol Optical Depth), DBAAEL (Deep Blue Aerosol Angstrom Exponent Land), NDDI(Normalized Dust Difference), Spatial Dust Pattern, Tehran Province.
Received: 2022/02/10 | Published: 2023/04/28
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