A numerical experiment of roadside diffusion under traffic-produced flow and turbulence

Abstract

Roadside air pollution due to heavy traffic is one of the unsettled issues in the atmospheric environment in urban areas. As a practical application of a Computational Fluid Dynamics (CFD) model, a coupled mesoscale-CFD model was applied to the Ikegamicho area of Kawasaki City, Japan. For this study, the effects of traffic-produced flow and turbulence (TPFT) on the dispersion of the pollutants near the heavy traffic road were mainly investigated in an actual urban area. First, a series of preliminary CFD calculations was conducted for a road tunnel field experiment to obtain a fitting parameter for the traffic-produced flow. The calculation was then performed for 24 h in December 2005 around Ikegamicho, and the results were compared with the data at a roadside monitoring post in the area, located 10 m from the boundary of the ground road. In general, the effect of traffic-produced flow and turbulence was limited at the downstream side of the roads. The maximum concentration of NO x was reduced and smoothed out along the traffic flow by the traffic-produced flow and turbulence on the road. The effects of traffic-produced turbulence on the dispersion of pollutants were greater than those of traffic-produced flow; however, the effects of traffic-produced flow were not negligible. The concentration of pollutants was not particularly dependent on the turbulent Schmidt number because most of the emission sources were introduced as volume sources in the present calculations, and the effect caused by differences in the material diffusion coefficient was not particularly significant at the outside of the road.