Analytical and Experimental Studies of Vehicle Pollution Dispersion

Using a dual approach of wind tunnel experimentation and the development of an ana-lytical model, the dispersion of pollutants from road vehicles has been investigated. A series of novel tests were conducted in an environmental wind tunnel which looked at the dispersion of propane in the wake of a 1=50th scale model of a lorry which was fired across the wind tunnel using a special rig. Time histories of concentration and air flow were taken as the lorry sped across the tunnel. Two experimental scenarios were investigated. The first, a simulation of a typical rural boundary layer, confirmed the existence of a wake behind the moving lorry. Concen-tration measurements revealed that the dispersion was largely Gaussian in nature and that at low cross wind speeds the vehicle-induced turbulence was the dominant mixing effect. Measurements were taken as the lorry passed along a model of an idealized urban street canyon. Time histories for individual firings exhibited two peaks as the propane was swept around the canyon in the resident vortex. Ensemble averages of several firing