Street Canyon

Traffic emissions have a significant impact on urban air quality, which particularly concerns street canyons, i.e. spaces with limited air exchange. Traffic emissions in street canyons create high concentrations of air pollutants. Based on measurements carried out for selected routes and model experiments conducted in a wind tunnel, it is shown that a roadway’s urban structure has a significant impact on concentrations of pollutants from traffic emission which enter buildings by means of mechanical and natural ventilation systems.

Traffic–related pollutant has been recognized as an air pollution hot spot due to its large emission rate and great health impacts for the exposed population. In the present investigation, a computational fluid dynamics technique is used to evaluate the effect of traffic pollutions on indoor air quality of a naturally ventilated building. The transport of street-level nonreactive pollutants emitted from motor vehicles into the indoor environment is simulated using the RNG k-ε model of the turbulent flows and the pollutant transport equations.

Toward the appropriate selection of urban heat island measures technology in the street canyon, the introduction effects of the technologies in the typical street canyon are analysed by the model calculation. It is appropriate to use street trees for the improvement of the thermal environment on the sidewalk and high reflectance paint or water-retentive pavement for the reduction of surface temperature on the roadway. Reduction of solar radiation gain to the sidewalk pavement surface is dependent on the location and area of the shadows by street tree.

To study the thermal effects on airflow in a street canyon under real heating conditions (due to diurnal solar radiation), a one-way static approach combining an urban canopy model and CFD is proposed in this paper. An urban canopy model was developed to calculate the individual temperatures of surfaces in the street canyon. The calculated surface temperature may be used as a thermal boundary for CFD simulation. The reliability of this model was validated against a field experiment in Harbin, China.

This study aims to investigate and clarify the effects of roadside trees and moving automobiles onoutdoor airflow distribution, turbulent diffusion of air pollutants and thermal environment within streetcanyons by means of the results obtained from field measurements in the central part of Sendai city,Japan. The detailed field measurements were carried out in the summer of 2006, at two streets withdifferent densities of roadside trees and traffic volume. The microclimate and NOX concentrations as wellas traffic volume were measured.