Quantitative Study Of Attenuation Effect Of Greenery On The Street Pollution Of Residential Areas

Nowadays,with the rapid urbanization and the increase of vehicle ownership,the problem of air pollution caused by exhaust emissions can not be ignored.As the main living space of urban residents,the indoor and outdoor air quality of residential areas is closely related to residents’ health.Because of the low exhaust emission of motor vehicles,the pedestrian height along the street settlements is the most vulnerable to the impact of exhaust gas pollution.In order to better improve the air quality of residential public space,it is necessary to find an effective way to improve the air quality.Green planting,as a means of improvement with low planting cost and more subsidiary effects,is more practical than traditional methods in changing district planning and architectural layout.In addition to the traditional improvement of wind,heat,sound environment and landscaping,green planting plays an important role in air pollution prevention.However,because there are many parameters to be considered in numerical simulation of green plant,the mechanism of canopy convection field is more complex,and the effect of different species,morphology and layout on pollution shielding effect is different.The mechanism of influence remains to be further explored.In this paper,the planning and layout parameters of 22 typical residential districts in northern China are summarized in advance.CO2 is used as a substitute for polluted gas,and PVC porous material is used as a substitute for the green model.Diffusion simulation is performed with the large-scale low-speed wind tunnel of Dalian University of Aeronautics.Taking the measured boundary conditions as the initial setting of CFD simulation,the accuracy of the simulation settings is verified and calibrated by wind tunnel tests.The results show the reliability of the CFD numerical simulation.Through CFD simulation,the shielding effect of green plants with different porosity on vehicle exhaust pollution was discussed.By changing the geometric parameters and layout form of green plants,8 kinds of green layout scenes were compared and summarized,and the typical influencing factors were summarized.And selected Dalian representative green plant collocation to carry on the actual scene arrangement.The results show that there are two effects of plants on the downwind pollution: one is to reduce the wind speed and the other is to block and shield the pollutants.When porosity > 0.14,the former occupies the dominant position,the downwind will form the phenomenon of pollutant concentration increasing.And with the increase of porosity,the pollution shielding effect will be worse,when porosity is less than 0.14,the latter will play a dominant role.The pollution concentration in the downwind direction will be reduced;only trees and no shrubs will be arranged,so the pollution shielding effect will be greatly reduced;reducing the width of green plants and increasing the height of green plants will be beneficial to the shielding of CO2 pollution.The study provides a reference for quantitative evaluation of the relationship between greening forms and pollutants,and provides a scientific basis for the adoption of corresponding landscape design measures to create a good living environment.