Physical Simulation of Automobile Exhausts Dispersion at an Urban Intersection – Part II: Traffic Induced Effects

Traffic induced turbulence coupled with natural air motions becomes an important variable affecting the dispersion of exhaust emissions, especially under low wind conditions. A flexible model vehicle movement system (ƒMVMS) for an urban intersection having two-way straight and radial peripheral traffic flows has been designed, fabricated and made operational in the EWT to study the traffic induced effects. The tracer gas concentration is measured, online, at hundred ninety two locations by gas chromatograph (FID type detector) at variable approaching wind directions, i.e., 0 0 , 30 0 and 60 0 and traffic volumes of 1200, 3300 and 5400 veh/hr. The percentage reduction in normalized concentration (K) values increases with increase in the traffic volume (‘no traffic’ conditions to 5400 veh/hr) and approaching wind angles (0 0 to 60 0 ). The maximum reduction in tracer gas concentration is 47% at 0 0 and 30 0 approaching wind directions when the traffic volume is 5400 veh/hr. The percentage reduction is significantly influenced when traffic and wind flow directions are opposite to each other. However, the reductions in K values decrease with height and reach its minimum value of 1.13% at the top of building blocks for all traffic volumes. At ‘innermost’ corners of the building blocks (facing the intersection), the percentage reduction in K values is more than at ‘mid’ sections of the