Southwest Zahedan Green Belt Design with Dust Reduction Approach

Introduction
One of the natural phenomena that cause disastrous damages every year especially in arid and desert regions of the world is sandy storms. About two third of Iran is located in arid and semi arid regions. Studies show that 14 provinces in Iran are affected by wind erosion. The province of Sistan and Baluchistan has more than 5 million hectares of desert area, which its 800000 hectares (about 16 percent of the mentioned area) are among active dust areas. Dust is one of the unfavorable climatic and environmental phenomena, which is getting far away from its regular cycle in recent years and happens frequently in the Sistan area. Existing dust particles in the air are a group of solid or liquid particles whose size is between 0/002 and 500 micron. One of most important causes of this phenomenon is the lack of suitable vegetation. Green belt acts as a complete cover surrounding the city and it will help avoiding the entrance of pollution and dust into cities. In recent years, dust pollution happens frequently in Zahedan city. In fact, as Zahedan has a dominantly arid climate, it won't be a new event but the extensive amount of dust entering the city through every wind has made living more difficult. The direction of most winds blowing toward Zahedan is usually south-west and north-east and they usually carry dust particles with them. The location of the two studied areas which are at the entrance of Zahedan-Khash road( Khalij Fars boulevard),the importance of considering visual beauty at the entrance of the city( the lack of sufficient vegetation at the moment effects its visual beauty),being in neighbor with populous places like universities such as medical science university, Quran sciences university and Payam Noor university and also being in neighbor with some important organizations are the most important reasons which make this area the most qualified for pre-required necessities for applying a precise investigation.
This study was fulfilled to present procedures to decrease dust level in Zahedan city and to bring air quality close to a range of 0-54 mg/m^3. In this study, existing 〖PM〗_10 particles in the air was measured. After defining air density index, air quality index (AQI) was determined by the use of T-test. Then the required width and length of green belt in order to lessen dust level up to clean air standards where determined.

Materials and Methods
The applied method in this study is a descriptive- analytical method. Its objectives are as following:
• To study the effect of mixed planting on the reduction of existing dust particle in the air in comparison to the existing vegetation.
• Determining the required width and length for the green belt in order to lessen dust level up to clean air standards(A: By using the statistical tests B: By considering city’s population)
• Selecting suitable plant species to be planted in green belt and recreational places considering the regions climate.
This research was fulfilled from April 2015 to March 2016 in order to study the density of the existing dust particles in air in two studied areas in Zahedan city. The first studied region consists of one hectare area in the southwestern part of Zahedan. This region has the poorest vegetation with limited number of Pine and Eucalyptus trees. The Distribution of trees and the dominant planting method especially in southwestern part is the same as the existing planting method in the first studied area. The second studied area has the exact area of the first region (approximately about 1 hectare) which is not located far from the first region. The second region is also located in the southwestern part of the city. This mentioned region dominantly has more different species in comparison to the first region which the total tree number is more than the first region.
The density of dust particles in the air was measured by using Grimm sample gathering – analyzing device in regular intervals with predefined periods (annual basis) for both studied areas. Samples gathered in order to evaluate the density of the existing dust particles in the air for both regions was performed once in every five minutes. But the data applied every three days based on the instructions of the U.S environment organization.

Discussion of Results
To measure the effects of mixed planting (in the second studied area) on reducing the volume of the existing dust particles in the air in comparison to the existing planting in the first studied area based on T-test, the following results are achieved:
To determine the length and width of the green belt in order to reduce the dust particles, two following methods are used: 1:By using statistical tests 2: By considering city’s population
The following equation was applied by the use of Excel Software:
(A1-A2)÷ A1×100= (137/77-128/44) ÷ 137/77×100
Based on the first equation, pollutant reduction level in the second studied region was estimated about 6/76 percent. As table 1 and equation 1 show, pollutant reduction level to approach this standard is evaluated as 80/40%.
137/77-27=110/77÷137/77=0/4080×100%=80/40%

Therefore, through adopting evaluated levels of clean air (80/40%) and pollutant reduction percentage which is 6/76, it is clear that suggested green belt area should be increased to 12 times of its existing area which is 1 hectare so that the green belt can have its most effect on the dust reduction.
X= 80/40÷6/76=12
To evaluate the green belt area, the second equation is applied.
Green belt area: 2A× A= 120000M2 A2 = 60000 A=244/948M 2 A= 489/88M
B: determination of green belt area depends on various factors like the main purpose to establish the green belt, the climate in the studied area, water sources, provided land to establish green belt, resided population, etc. Based on Table 3, to establish a green belt which its main action is to reduce dust particles in the air, about 〖3m〗^3 of green area per person is necessary for everyone living in Zahedan city.
Considering the population based on 2011 census, the total capital is obtained as follow: 660575×3=1981725
Therefore, based on the second equation, green belt width and length was evaluated:
Green belt area (m^2) =2A× A= 1981725M2 A2 = 990862/5 A=995/420M 2 A= 1990/84M
Because the statistical method is an exact method to measure the green belt area, the estimated area by statistical method is used and applied in the process of designing the green belt in Zahedan city.

Conclusion
Based on the present study, data gathering in an annual period (From April 2015 to March 2016) was performed in the two regions located in southwestern part of Zahedan city, one with existing planting and the other one with mixed planting (second studied area). Using the mixed planting method can cause 6/77 % reduction in the amount of existing dust particles in the air. Therefore, through applying T-test and considering population, the suitable area was estimated. In the T-test method, the suitable area to establish green belt was estimated about 120000m^2. In addition, considering population and required capita for green space to decrease dust, the suitable amount of area to establish green space was measured about 1971725m^2, by using presented tables for expectations from green space. To identify local and resistant plant species to dust, plants with the following characteristics were selected: downy leaves, speared leaves, low water requirement and adaptable in every soil especially weak soils. Some suitable cases are Tehran pine, Tamarisk, Shiraz cedar, Silver cedar, Eucalyptus, Ailanthus, Pomegranate, Buckthorn, and Berry.