The Effect of Vertical Green Surfaces in Improving the Quality of Urban Climate With an Emphasis on Improving Air Pollution and Temperature Parameters (Monograph Case Study: Green Wall of Nature Bridge, Tehran)

Tehran is not a suitable place for pedestrians today. Air pollution and rising temperatures are the most important issues that cause this. Considering the existing density in urban spaces, one of the solutions that don't occupy the land area while having plants and enjoying their benefits is vertical and horizontal green surfaces or in other words, green walls and roofs.Therefore, this study aimed to investigate the effect of the urban green wall on air pollution and temperature. In this study, the Hedera helix plant of the green wall of Tehran Tabiat Bridge has been selected for further analysis of the subject. What will be investigated in this research is the effect of urban green walls on two factors including temperature and air pollution. Considering that the increase in air pollution can be a significant factor in creating global warming, and the temperature rise also leads to an increase in the number of secondary pollutants, these two parameters directly affect each other. Hence the difference between this research and the previous studies is that both of mentioned factors are questioned here. Furthermore, another difference is that most of the past research had examined urban walls in direct connection with the pollution caused by street traffic; however, in this research, the green wall of Tabiat Bridge, which is located at a height of almost 40 meters with markable distance from streets and pollutants such as cars, has been investigated. Therefore, the hypothesis of this research has been questioned in two phases. This hypothesis can be expressed in the form of this statement that the use of creeping plants including Hedera helix in urban green walls has an effective role in reducing air pollution and adjusting air temperature in hot seasons. This research aims to answer these questions, how much do plants growing in urban green walls reduce pollution and air temperature? According to the types of these plants, how far from the green wall this reduction may happen, and to what extent is it effective?

In two phases, this study measured the extent and effect of the green wall on temperature changes and pollutants in the air. In the first phase, temperature changes were measured by four data loggers simultaneously at distances of 0, 0.5, 1, and 2 (points A, B, C, and D respectively) from the green wall and a height of 1.5 meters from the bottom of the bridge. Field harvesting was done in three days of the summer season (July 5 to 8) from 10:00 to 14:00. (The average temperature in these three days is listed each half hour in the graphs.). According to previous research results, the green wall's temperature effects happen regardless of the type of plant. Therefore, this phase of the study was carried out regardless of the type of hedera helix. The second phase was done by sampling the plants on the wall, checking the amount of sulfate and nitrate pollutants in it, and comparing this amount with the values ​​of previous research. The reason for choosing these two pollutants in this research is the predominant volume of these two pollutants caused by the traffic of cars in polluted urban air. In the sample studied in this research, there are two types of Gracilis and Pedata Hedera helix plants, and in addition to the total absorption of the pollutant by the plant, the amount of absorption of these two species has also been compared with each other.

The results of this study indicate the effect of Hedera helix plant on temperature reduction. In hot seasons, it is effective only about 0.5 meters from its wall and it is not effective in further points. At best, the effect of temperature reduction of this wall occurred at point A with a distance of zero from the wall, about 0.8 °C, in comparison to points C and D with temperatures close to the outside air. The results of the second phase show that in the hooded Hedera helix type, the absorption rate of sulfate is 2 times and nitrate absorption is about 1.2 times more than the green type. To determine the amount of air quality, the more pollutants plants have absorbed, the more effective they will be in improving air quality by reducing pollutants. Therefore, in this research, it was shown that Pedata Hedera helix works more effectively than Gracilis Hedera helix to reduce air pollution.

Based on the results of this research, creating green walls using cheap plants, compatible with Tehran's climate and with rapid capital growth in Tehran can be used as an effective solution to absorb pollution caused by urban traffic and vehicle fuel. Furthermore, a comparison of two samples of the bridge and urban sample indicates an 18 times increase in sulfate concentration and 6.8 times in the nitrate concentration in the urban sample compared to Tabiat bridge. As a result of analyzing and comparing the example of the green wall of Tabiat bridge with other urban green walls, it can be concluded that being away from the polluting source as well as creating a covered space in order to control the radiation factor increases the efficiency and effectiveness of these green walls.  In addition to reducing pollutants, the effect of green surfaces in temperature adjustment is a very key factor. Although the effect of these walls in temperature reduction just happens in the close spaces near the wall, taking into account that the use of these green systems can happen on an extended scale the result will be remarkable. Considering the pollution conditions of cities today and proving the effectiveness of green walls in solving this problem, this issue will continue to be very important in creating sustainable cities in future research. Among the proposed topics, we can mention the effect of different implementation methods and the type of climbing plants or implementation system used in the green wall, and their efficiency and effectiveness.