Spatial variability of pollution induced by traffic in street canyon.

Concentration of pollutants produced by car traffic in a street below the roof level has large spatial variations. In a street, pollutants are diluted by the turbulent air flow which is induced by the wind speed above the roof level, and also produced by car displacement. The airflow structure is in relation with street size and building shape. Particularly strong gradients of concentrations can be observed vertically and also horizontally in front and along buildings where are set up ventilation inlets and windows. So it is necessary to take into account this variability to consider the influence of outdoor air upon indoor air quality. The street canyon case has been studied extensively in recent years by CSTB and many other authors. A bibliographical synthesis is presented, including results from field measurements, wind tunnel experiments and numerical simulation.