Study on influence of viaduct and noise barriers on the particulate matter dispersion in street canyons by CFD modeling

This paper investigates the influence of viaduct, noise barrier, and the ratio of leeward and windward building height (H1/H2) on flow regime and particulate matters (PM) dispersion in an urban street canyon, using Computational Fluid Dynamic (CFD) simulation. Results show that viaduct introduces more sources of particulate and influences the flow pattern significantly. New vortexes form when noise barriers set up along the viaduct and influence the flow around the viaduct and distribution of pollutants at the center of the canyon but influence to a less extent in the key breathing zones. When the street canyon is symmetric, barriers can reduce the peak value of pollutant concentration at buildings wall, and lower the integral concentration in zones that affect people's breathing. When the street canyon is a step-up type (the leeward building is lower than the windward one), barriers affect to a less extent the PM distributions at buildings wall and breathing zones. Increase of the height of windward buildings hinders the diffusion of pollutants. Furthermore, people living in the windward building or walking on the street have to suffer more from the pollutant. When the street canyon is a step-down type (the leeward building is higher than the windward one), H1/H2 = 6/5, pollutants still gather at the leeward wall. It has the least integral pollutant concentration in the zone near buildings and street. H1/H2 = 2, pollutants are transported to the windward wall and accumulated because of the upper main vortex in the canyon. Pedestrians' breathing zone is extremely high compared with other configurations.