Review of Dispersion Characteristics of Vehicle Emission Pollutants in Urban Street Canyons

The dispersion characteristics of vehicle emission pollutants in street canyons depend on roof level wind speed and direction,and are affected by street canyons width/height ratio and symmetry,and the shape and building heights distribution of blocks surrounding line sources.Pollution concentrations in street canyons with canyons width/height ratio around 1,with step\|up notch configuration or with wider street are relatively low.Street level concentrations can be significantly reduced by introducing variable geometry designed specially to increase dilution in the immediate vicinity of the line source.It is concluded that the consideration of the above factors in construction plan may bring pollution levels down.