Study On PM2.5 Pollution And Numerical Simulation Of Street Canyon In Chongqing

With the rapid development of China's economy and urbanization,people's living standards have been improved,and motor vehicles have gradually become an indispensable means of transportation in people's daily lives.However,with the increase in the number of cars,there is a serious air pollution problem along the road,and PM2.5 is one of the main pollutants affecting air quality.The development of the city has formed a city street canyon.In the urban street canyon,the air circulation is poor,and the pollutants are more likely to gather.This is very harmful to the health of road pedestrians.Using the dust-removing effect of green plants and greening in the street canyons can effectively improve the atmospheric air quality.Therefore,it is necessary to study the distribution law and related influence factors of PM2.5 in urban street canyons,and explore the influence of different green forms on the mass concentration of PM2.5 and the removal effect.In this paper,the combination of experimental measurement and numerical simulation is used to study the influence of natural factors and greening methods on the mass concentration of PM2.5 in street canyons.Through the actual measurement method,among the influence factors such as traffic flow,atmospheric temperature,atmospheric relative humidity and distance from receptor distance from pollution source,the most important influence on the mass concentration of PM2.5 is the distance between the receptor and the source of the pollution.The specific order is: Receptor distance from pollution source > Atmospheric Relative Humidity > Atmospheric Temperature.Among them,in the street canyon,when the traffic volume changes little,the relationship between traffic flow and PM2.5 is not clear;the relationship between atmospheric temperature and relative humidity and PM2.5 is segmented: the atmospheric temperature is not more than 30 °C and the relative humidity is less than 70%,the mass concentration of PM2.5 is significantly positively correlated with atmospheric temperature and relative humidity.When the atmospheric temperature is greater than 30 ° C and the relative humidity is greater than 70%,the mass concentration of PM2.5 has a significant negative correlation with atmospheric temperature and relative humidity.The mass concentration of PM2.5 will decrease with the increase of the distance in the horizontal direction,but it will accumulate in the front part of the building,resulting in an increase in the concentration of PM2.5 before construction.In the vertical direction,the PM2.5 mass concentration change is more complicated.Due to the wind climbing effect,the lower pollutants will be diffused to the middle and upper parts,resulting in an increase in the PM2.5 mass concentration in the upper part of the building.By simulating the effects of different greening methods in the center of the street canyon on the distribution and removal of PM2.5,it was found that a row of trees,shrubs,or a combination of trees and shrubs in the middle of the street canyon has little effect on PM2.5 distribution in horizontal and vertical directions.The difference is that the greening of shrubs will alleviate or even eliminate the accumulation of PM2.5 in front of buildings,which is important for optimizing the indoor air quality of low-rise buildings.In the horizontal direction,the three green forms can reduce the concentration of PM2.5 more than in the vertical direction,and the greening method combined with trees and shrubs has the most significant effect on the purification of PM2.5.The combination of greening and arable compared with no greening,the average purification efficiency of PM2.5 is 14.7% in the horizontal direction,and the average purification efficiency of PM2.5 in the vertical direction is 4.375%.