A Numerical Simulation of Tracer Gas Diffusion in a Real Urban Street Canyon in Tokyo
Recently, air pollution in Japan has decreased considerably due to the implementation of emission regulations. However, the environments at road side monitoring stations in urban
areas still exceed regulation limits and some counter measures are required. To improve these situations, the mechanism of atmospheric dispersion must be clarified and modeled together with the emissions of pollutants by automotive sources. Simulation models must be easily adaptable to account for different characteristics of surrounding building and meteorological conditions. In these respects, numerical simulation models are superior to wind tunnel experiments or the other tools. In this study, tracer gas diffusion in a real urban street canyon in Tokyo was simulated by the computer program FLUENT. The objective street canyon is about 400 metres long, 33 metres wide and is surrounded by buildings of six to ten floors in height. We constructed the geometrical model of the target area of about 400 by 600 metres and set it in the center of a multilateral column of sixteen faces with a radius of 1250 metres and 1000 metres high. The wind enters from four neighboring faces and by this construction we can easily change the inflow wind direction. The tracer gas concentrations were well simulated by the model and a correlation coefficient of 0.82 were obtained.