Large Eddy Simulation Of Urban Heat Island And Pollutant Diffusion

Along with urbanization, more and more people are migrating to urban areas and the dimensions of urbans are expanding. As a result, urban heat island effect and air pollution problem become increasingly serious. To im-prove our living environment and even the global climate, researches on urban environment issues play a significant role. Among the researches, numerical simulation methods which are supported by the development of turbulence models and computer's computing capacity are more and more widely used.In this paper, the urban heat island effect and air pollution dispersion in Beijing are simulated with large eddy simulation (LES).Advanced Regional Prediction System (ARPS) is chosen as the basic computing program to solve three-dimensional compressible N-S equations.In order to truly reflect the characteristics of urban underlying surface in this meso-scale model, this paper improve model of surface characteristics'according to the actual land cover types of Beijing in 2005. Additionally, the parameterized models of anthropogenic heat and buildings'passive scalar diffusion are added to this model. After the revision, the simulation result by this model generally agrees with field monitoring data.This paper gives a comprehensive analysis to the influential factors of the heat island effect. The effects of anthropogenic heat, surface albedo, ve-getation and building resistance on the wind, moisture and heat in the city are investigated respectively. The results of this paper indicate that anthropogenic heat emissions and reduced surface albedo are the main factors contributing to the effect of urban heat island in night and day respectively. Reduction of the coverage of urban vegetation can increase the diurnal range of temperature while buildings have a complex effect on the heat transfer between the at- mospheres and land surface.Based on the investigation of urban heat island effect, this paper goes on to simulate the dispersion air pollution from traffic and high chimney power plants. The results show that, during the daytime, the pollution from high chimneys reaches the ground easily due to the strong vertical convection. But it is difficult because of the stable layer of atmosphere at night. Accordingly, it is observed that the maximum concentration of pollution near the land sur-face is lower. What is more, the pollution's landing position and its source are further away from each other horizontally. To stimulate the traffic pollution, one-way nested grid method is used in order to reduce the scale to be com-puted and increase the grid resolution. Besides, the Coupling method of Gaussian model and numerical model is used to overcome the difficulty in recognizing roads.Although the parameterization of building resistance and anthropogenic heat model are added into the numerical model, the model of underlying sur-face is built with uniform parameters. More detailed urban canopy paramete-rization modeled should be created so as to reflect the complex three-dimensional structure of the urban more truly.