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Behroz Nasiri , Zahra Zareei Chaghabalaki, Mansour Halimi, Mohammad Rostami Fath Abadi,
Volume 3, Issue 2 (5-2016)

One of the most important components of the extent of pollutants mixing and air quality at near the Earth's surface is the height of boundary layer. Many variables involved in determining the height of the boundary layer of atmosphere. Although all of the troposphere (the lower ~10km of the atmosphere) is affected by surface conditions, most of it has a relatively slow response time. The lower part of the troposphere that is affected on a shorter time scale is commonly defined as the Planetary Boundary Layer (PBL). The depth of the mixed layer has a significant effect on the concentration of air pollution, which itself is dependent on the intensity and duration of solar radiation and wind speed. According to Stull, one can describe the planetary boundary layer as “that part of the troposphere that is directly influenced by the presence of the earth’s surface, and responds to surface forcing with a timescale of about an hour or less.”  Surface temperature has a strong relationship with height of the PBL. As the surface cycles between daytime radiation and nighttime cooling the amount of convection taking place changes. When the temperature gradient is steep, more convection takes place to dissipate thermal energy in the most efficient manner. In other words, the greater the temperature difference between the surface and the lower troposphere, the higher convective eddies must reach to alleviate the gradient. Relating this to Stull’s definition of turbulence, it can be concluded that the height of the PBL varies with surface temperature. In fact, the spatial range of the PBL can vary from less than one hundred meters to several kilometers. The strong relationship between convective turbulence and height of the PBL is sometimes used to define the boundary layer and call it the Convective Boundary Layer (CBL). Analogous to the Stull’s definition but focusing on turbulence, Lloyd et all describe CBL as “a layer of air typically of order 1km in depth, well mixed by turbulence maintained by buoyancy due to heating at the ground. It is bounded above by stably stratified, no turbulent air and grows through the day.  In this study we aimed to analysis the status of ABL in 3 dust period days in Khuzestan province of Iran.

The Data were used in this study includes: The Daily data of dust concentration during 27Jan to 1 Feb 2015, the daily height of ABL also were used. The daily data of ABL were given from ECMWF with 1/8 degree spatial resolution. We used the Pearson correlation and synoptic analysis to assessment the condition of boundary layer at the mentioned days. For analysis the characteristic of ABL the climatic data of Wyoming University were used to assessment the thermodynamics of atmosphere. The spatial distribution of ABL height at the dusty day also were used for 12 UTC.

The results indicated there is the direct relationship between the ABL height and the concentration of dust in the mentioned days. So that in the days that the concentration of dust reaches maximum we fund that the height of ABL reaches maximum simultaneously and vis versa. The spatial distribution of ABL height shown that the height of ABL in the 29Jan reaches maximum that the maximum concentration of dust related to this day. And also the minimum concentration of dust observed in 27Jan and 1Feb that the in this day the height of ABL was minimum. The synoptic analysis also reveals that locating the low pressure system at the 500hp level that the Khuzestan province has been locating at the front of this system lead to transport the dust to study area.

In this study we reveal that the height of ABL in the dust days of Khuzestan has a totally revers behavior in compare to the air pollution days in Tehran. In the pollution days in Tehran the lowing of ABL height and inversion lead to intensify the concentration of pollution while in the dust days of Khuzestan the height of ABL were increased in compared with non-dusty days.

Hasan Jems, Saman Maleki, Abuzar Nasiri, Soraya Derikvand,
Volume 10, Issue 1 (5-2023)

1- Introduction
Desert dust is formed under the influence of the special weather and environmental conditions of desert areas, enter the atmosphere. Localized hurricanes caused by ground air instability and sweeping dry deserts clear silt and sand particles enter the atmosphere from the surface. Ecologically as well as physically desert dust Effects such as pulmonary heart disease, disruption of plant physiological circulation, and erosion of growing structures include heavy metals deposited on soil surfaces, water surfaces, and canopies Plant surfaces that cause chemical changes and physiological damage to environmental ecosystems. Difficult Metal generally refers to a group of metal elements with a specific gravity of 6g/cm3 or more. Atomic weight greater than 50 g. Heavy metals important from an environmental point of view Cadmium, arsenic, cobalt, vanadium, zinc, mercury, iron, manganese, nickel, lead, chromium, copper, that do not decompose naturally. In addition, the long life of heavy metals is also considered. In the studies that have investigated the effect of dust on citrus fruits, it has been very few and even garden plants have been done on a case-by-case and limited basis. Citrus and especially oranges are one of the important and economic garden products in Iran, which are cultivated in tropical areas with mild and cold winters. Khuzestan plain, especially Dezful, is one of the poles of citrus and orange cultivation. But in Khuzestan, it is under the influence of many environmental stresses, which can be mentioned as drought stress and air pollution in the region. The rising trend of the phenomenon of desert dust in recent years has been shown as a danger and its effect on the environmental health and economy of the region is very severe, and the most damage has been reported to the agricultural sector. Although the damage caused by micro-pollens to the agricultural sector is expressed as an economic figure, the effect on plants, especially citrus fruits, remains unknown. Although researchers have studied the effect of fine dust on sugarcane, grapes, legumes, nectarines and peaches in Iran, India and Pakistan, the effect of fine dust on vegetative traits and orange fruit has not been investigated in Khuzestan. Considering that the first step in controlling the effect of air pollution on plants and horticultural crops is to know how it affects the plant, on this basis, the main goal of the current research is to reveal and evaluate the effect of micro-pollens. Desert is on vegetative and reproductive characteristics of Thomson orange in Dezful.

2- Methodology
In order to evaluate the effect of desert pollen on the quantitative and qualitative yield of orange fruit, Thomson variety, a field experiment in the form of randomized complete block design with four treatments and three replications was carried out in Dezful in 2018-2019. The treatments included 1) road dust and desert fine dust, 2) desert fine dust, 3) washing after the occurrence of fine dust and 4) control away from fine dust. The chemical and functional characteristics of the trees were measured after applying the treatments, which included chlorophylls a and b, relative water content of the leaves, number of fruits, diameter and weight of the fruit, soluble solids of the fruit and the final yield of the tree.

3- Results
The results showed that chlorophyll a decreased by 21% and 11%, respectively, in the road dust and desert fine dust treatments compared to the control. Chlorophyll b also decreased to the same amount compared to the control. The diameter of the fruit also decreased by 20% in the desert dust treatment compared to the control. The number of fruits per tree also decreased by 22 and 20% in the treatments of pollen and fine desert dust compared to the control. In the product yield of each tree, in the treatments of road dust combined with desert fine dust and the second treatment, which was only desert fine dust, it decreased by 22 and 17 percent, respectively, compared to the control. Tukey's mean comparison showed that the difference of all quantitative and qualitative characteristics between the treatments was significant and Desert dust has a negative and decreasing effect on the yield of Thomson orange trees; However, washing the trees after the occurrence of micro-pollen removed the effects of micro-pollen on the performance of trees and it even increased compared to the control; So, washing increased the yield of oranges by 40, 35, and 12 percent compared to the first and second treatments of road dust and fine dust, as well as the control.

4- Discussion & Conclusions
Plant growth cycle and biochemical interactions of plants show different reactions under the influence of environmental stresses. The results of previous studies indicated that fine dust and dust storms have been identified as an environmental stress for plants that have a negative effect on grapes, medicinal plants, sugarcane, nectarines, peaches and legumes. The effect of fine dust on the plant can be investigated in several characteristics and periods of plant phenology. In the first stage, the deposition of desert fine dust on the leaves of the plant causes shading and reducing the light received by the leaf pigments. Fruit formation is the most important phenological period of the plant, and the occurrence of environmental stress can affect the yield and products of the plant. The present research showed that the number of fruits in orange trees showed sensitivity to desert pollen and the settling of soil particles on orange flowers reduced the amount of fruit formation and finally the number of healthy and ripe fruits in the trees treated with road dust and Desert fine dust decreased compared to the control. Finally, the yield of control orange trees decreased by 17% and 22%, respectively, compared to desert dust and road dust treatment with desert dust. The yield of cotton plants in China decreased by about 28% compared to Desert dust. It can be concluded that although desert dust and road dust reduce the yield of Thomson orange fruit, washing it compensates for the damage and will be economical from the economic point of view.

Key words: Citrus, Photosynthetic pigments, Fruit yield, Dust, Dezful


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