The influence of a viaduct on PM dispersion in a typical street: Field experiment and numerical simulations

Özet

To investigate the effects of a viaduct on particle diffusion below the viaduct, field measurements for particulatematter (PM) concentration along roadsides with and without viaducts were conducted in this study. Air flow andparticle (PM2.5) distribution around a viaduct were simulated by Computational Fluid Dynamic (CFD) equippedwith the Discrete Phase Model in a Lagrange coordinate system. Experimental results of this case study indicatethat the average mass concentrations of PM10 (156.7 μg m−3), PM2.5 (77.3 μg m−3) and PM1 (56.5 μg m−3) onan elevated highway exceeded those on the ground–level expressway by 15%, 10% and 12%, respectively.Simulation found that two main vortices as well as two or three secondary vortices are generated in the canyonwhen both a viaduct and a barrier are added, while there was only one main vortex in the street canyon withouta viaduct. A viaduct causes the particulate matter to be distributed unevenly, and the concentration on theleeward side near the ground is the highest. The vortex center is elevated as the value of ΔT (ground–level airtemperature) increases, but the concentrations are basically maintained. We concluded that a viaduct increasesthe concentration of particulate matter in the street canyons and greatly affects the airflow field. Both ΔT and asound barrier on a viaduct reduce the PM concentrations, but the effects are limited.