Abstract
We conducted wind tunnel experiments using a simplified 2-dimensional model of an existing urban area to study the relationships between the concentrations of pollutants on and around the main road and the structure of the road and the atmospheric stability.
In the study area, a fence covered with thick ivy has been installed between the piers of an elevated roadway in an effort to reduce the localized high concentrations of air pollution along the roadway. However, by obstructing natural ventilation beneath the elevated roadway, it seems that the fence actually increases the concentration. We closely measured the concentration distribution of pollutants in and around the main road, examined the effect of the fence, and discussed ways to reduce the localized high concentrations in and around the main road.
The main results are as follows:
1) Within the range of this experiment there was no pronounced tendency for high concentrations to occur on the ground-level road beneath the elevated roadway when the air pollutants were discharged on the elevated roadway.
2) Concentration distribution changed dramatically with the structure of the main road (existence of the elevated roadway, existence of the fence, etc.). However, in the surrounding area, the differences in concentration due to the structure of the main road diminished as the distance from the main road increased.
3) Atmospheric stability has a large influence on roadside concentration. Large differences in concentration under neutral and stably stratified conditions were also seen in the surrounding area; these differences in concentration increased with distance from the main road.
4) The fence may obstruct the natural ventilation beneath the elevated roadway, thereby increasing the area of localized high concentration.
5) Ground-level concentration can be reduced by directing some of the traffic on the ground-level road to the elevated roadway.
