عنوان مقاله [English]
The subject of this paper is to investigate the effect of the amount of enclosure of urban pedestrians as well as the type and amount of vegetation on the amount of air suspended in Tehran. The results of the previous studies show that vegetation and physical patterns of urban space have a significant effect on the rate of airborne particles. The research seeks to answer these questions: What is the relationship between the amount of enclosure in the pedestrian streets urban spaces and the amount of suspended particles? And also how does the type and amount of vegetation and location and its severity affect the amount of airborne particles? The purpose of this study is to identify the optimal amount of physical enclosure of city walkways as well as vegetation type and their size and their distance, and the density of their leaves, in order to reduce the airborne particles contaminated with particles less than 1 micron (PM10). The research method in this paper is descriptive analytic and simulation using Envi-met software.
Pedestrians are special pedestrian crossings that are implemented to create a suitable and safe environment for pedestrians by imposing a complete or relative ban on the movement of motor vehicles in some passages (Hakimi, 2014). Pedestrians are crossings with the highest level of social role in which pedestrians are completely dominated and motorized vehicles are used only to serve the current life in the crossing. Sidewalks are a tool for collective activity (Pakzad, 2014). In recent years, the increase in air pollution has made urban public spaces less usable for different segments of the society, so that one of the most important environmental challenges facing metropolises is the phenomenon of air pollution (Yeganeh). et al. 2018).
Air pollution is the presence of one or more pollutants or compounds in the external or internal atmosphere, in amounts and duration that may cause damage to human, plant or animal life or property and unreasonably interfere with the comfortable enjoyment of life or property (Ajlali, 2016). Air pollution is not caused by a single factor, but a series of complex issues cause air pollution. In fact, a part is related to the industry, a part is caused by cars, a part is related to meteorological parameters (such as wind speed) and some cases are also related to geographical conditions such as mountains, seas, the slope of the region, etc. (Shafipour) , 1387). The unfavorable condition of the air and the concentration of pollutants exceeding the limit set by the World Health Organization (WHO) in metropolitan cities are considered a serious threat to the health of citizens. The city of Tehran, as the largest and most populous city in the country, has a problem due to specific geographical (topography and weather), social (population distribution and traffic), cultural (level of culture and related education) and urban development conditions. It is air pollution (Air Quality Control Company, 1390: 12). One of the ways to optimize the environment in order to provide thermal comfort and remove air pollution is to use plants (Bourbia, Boucherriba, 2010). Planting plants on the surface of roads, increasing the planting of plants on the roofs of buildings and increasing greenery in the city will reduce urban heat islands, reduce energy consumption and improve air quality (Bourbia F, Boucherriba F. 2010; 35). Plants are able to absorb pollution better than artificial surfaces and buildings, which is proved by the chemical analysis of the foliage surface (Beckett, Freer-Smith, Taylor, 1998; 99). In a research conducted using a wind tunnel, it was shown that the presence of trees on the street surface increases the presence and concentration of pollutants in the roads (Gromke C, Ruck B, 2007; 41).
Dust removal is one of the important environmental effects that urban green spaces are responsible for. Green plants absorb fine particles of dust, bitumen and oil, and as a result, the speed of dust that hits a mass of greenery is reduced. Heavy dust settles and smaller particles stick to the surface of plant leaves. Grass absorbs dust 3 to 6 times more than bare surfaces, but the same grass absorbs dust 10 times less than a tree with the same surface (Yang, J., McBridea, J., Zhou, J., Sun, Z., 2005)
Pollution removal is one of the various ways of the effect of urban trees in improving the city air, therefore, tree planting management based on shading and choosing the appropriate plant species can be a sustainable strategy to improve the city air and bring it closer to the standards. be a city Therefore, it is better to use plants that have the ability to absorb environmental pollutants in planting combinations. To increase purification, plants that occupy more space per surface area can be used or combined with green plants, which is based on size, color, compatibility, etc. Taghizadeh, 1387.
This article aims to study the effect of vegetation and the degree of confinement in urban sidewalks on the dispersion of airborne particles in the city of Tehran, with an emphasis on suspended particulate matter less than 10 microns or PM10. Among the sources of emission of pollutant M10, we can mention the indiscriminate construction in the city, the activity of brick making and asphalt making units around the city. The lack of green spaces and forest parks and the lack of suitable vegetation in the suburbs are also among the main factors in aggravating the pollution of suspended particles during storms and strong winds (Hava Health, 2016).
Methods of data collection at the theoretical level by referring to scientific documents and texts and at the experimental level, using data from databases related to climate variables and databases related to air pollution measurement (Meteoblue, ASPA's STREET) Physical, spatial, activity-social and symbolic sequences are studied (Yeganeh, Bemanian, 2012). The observation unit includes sequences and transversal and longitudinal sections of the thirty-third axis of Tehran city. Software analysis technique has been done with leonardo software. The variables include air pollution and the degree of confinement in urban pedestrian axes. This variable is the causal conditions for the dependent variable and the amount of air pollution is the dependent variable in this research. The determined indicators have the validity of the standard due to the fact that they refer to previous researches and common and accepted indicators of researchers in the field of landscape architecture and urban planning. In addition, the indicators have construct validity because they are determined based on the theoretical framework of the research. The reliability of the results of this research is due to the validity and citation of the software used in this research (Envi-met), which is cited in most theses and articles and scientific research related to the subject. It is
• Operationalization of variables
In defining the concepts and their practical identifiers, the experimental background and the theories discussed in the theoretical literature have been used. Based on this, the variables used in this research are conceptually defined as follows:
Conceptual definition of sidewalks: Sidewalks are passages with the highest level of social role, in which pedestrians have full control and motorized vehicles are used only to serve the current life on the passage. Sidewalks are a tool for collective activity (Pakzad, 2014). In determining its quality, factors such as vegetation, the relationship between mass and space, and the speed and direction of wind flow are of great importance.