The Study Of Atmospheric Particulate Matter Concent- Ration In The Street Canyon Under The Viaduct

With the speedup of urbanization and increasing of car ownership in China, urban air quality becomes worsening so that the ecological environment deterioration. The existence of the street canyon makes various harmful emissions difficult to diffuse due to the specific environment, which is harmful to the microclimate. Using field measurements, this thesis has studied the effects of four factors on the particle diffusion, which are ambient temperature,vegetation coverage near the buildings, whether there is a viaduct or not and the height.This study has made field measurementson particle concentration in street canyon under the viaduct on the Zhongshan West Street, in Changning District in Shanghai. The field measurements has been made in typical summer and winter months( two period from May 2015 to July 2015 and from January 2016 to March 2016), when the mass concentration of PM10 and PM2.5being tested. Then the study has discussed the effect of different factors on particle concentrationin street canyon.Also this thesis has used CFD software to make a model analysis about the diffusion of particle concentration in street canyon under the viaduct. After that, this thesis has made a comparative analysis between the measured data and simulated result.Since the conventional line source diffusion model is not applicable to the coverage of viaduct street canyons, this study makes the ambient temperature and the height of the valley Street particle concentration correlation analysis. Five conclusions have been made. Firstly,the lower the temperature of the micro-climate inside the street canyon, the higher the concentration of particulate matter within the street canyon, both negatively correlated. Secondly, the higher the vegetation coverage near the buildings is, the stronger the function of blocking out the particle below three floors will be. Thirdly, the particle concentration in street canyon is higher when there is a viaduct compared with when there is not. Fourthly, the height of the particle is negatively correlated to the particle concentration in street canyon. That is to say, the higher the street canyon is, the lower the particle concentration in street canyon will be. And there is an uprush of the particle concentration on the fourth floor when street canyon meets the same height of the viaduct in the height direction. Fifthly, By using FLUENT software under the viaduct in the street canyon of particle diffusion velocity and concentration distributions in the simulation,the breathing layer of the street canyon(about 1.5 m) do concentration diffusion distribution analysis finding that the maximum concentration value from the location of the building is about 5 metersand has a maximum value of the viaduct covered street canyons particulate matter concentrations higher than under no viaduct covered concentration of about 1.5 times.