Abstract: In order to predict the vehicle impact on air quality in a city street,an investigation was carried out by numerical simulation and wind tunnel experiment to evaluate pollutant dispersion in an urban street canyon flanked with arcade.This paper presented some interesting results.A clockwise vortex with its core in upper part of street canyon forms within the urban street canyon flanked with arcade,and a counterclockwise vortex forms within the arcade near the windward side of buildings simultaneously.The "climbing wall effect" occurs at the leeward side of buildings.Because of the influence of the arcade,the general pollutant concentration in the street increases greatly,and the concentration within the arcade is very high especially at the leeward side.

Key words: urban street canyon, arcade, wind-tunnel simulating test, numerical modeling, fluid flow, pollutant dispersion