Abstract
Green infrastructure has been considered as one of the remedies for air pollution. The positive effects of forests on air quality through deposition and uptake and air pollution abatement through aerodynamic effects of roadside trees are often studied, but the aerodynamic effect of forests has not yet been analyzed. This paper aims to investigate the transport of air pollutants in forests from an aerodynamic perspective by means of wind tunnel experiments. The porosity of the model tree was estimated to be roughly 30% from our wind tunnel experiment for a row of model trees and computational fluid dynamics simulations considering the shelterbelt drag force (Wang and Takle, 1997). The wind tunnel experimental results for a sparse forest showed a decrease in the tracer gas concentration from the windward side to the leeward side of the forest. On the other hand, there were minimum concentrations of the tracer gas in the center of a dense forest. This is because the dense forest induces a recirculation zone behind the forest and the tracer gas inflows into the forest from both the windward and leeward sides. It is deduced from turbulence statistics that the mass exchange through the canopy crown of the dense forest is lower than that of the sparse forest.
