Influence Of Surrounding Buildings On The PM10Diffusion At Road Intersection

Along with the rapid development of urbanization, air pollution of regionalenvironment and traffic road increase significantly. Inhalable particulate matter (alsoknown as PM10), floating in the air for a long time, thus has become the primarypollutant of city. Considering the heavy traffic flow, a great number of buildings andthe large crowds, the intersection cross has become a prominent area where the urbanpollution is significant. In particular, the distribution and height of buildings around thecity street will directly determine or influence the characteristics of inhalableparticulate matter (PM10) near the intersection cross of road.In this paper, several representative sampling points were labeled in theintersection blocks to analyze the influences of buildings layout and height on PM10features. On this basis, three typical road intersections in Xi’an were investigated andflow field, the PM10concentrations field and PM10distribution around the sidewalkwere obtained. The results may provide a reasonable foundation for municipalplanning and urban environmental protection.Compareing the field experimental results and different turbulence models, andfinally the Realizable k-ε turbulence model was chose as the suitable model to simulatethe diffusion and distribution of PM10around road intersections.Under a certaindominant wind, which has a angle with the reference direction of selected streets, theanalysis about the impacts of different building height shows that, the increase ofheight of upwind building at upstreaming would lead to the decrease of wind speeds ofthe streets and the reduction of PM10fluctuating for the sampling points. While theheight of upwind building at upstreaming has little influence but makes the wind speedof downwind streets increased, thus the PM10concentrations of the sampling points on both sides of the building decline sharply. For the building that is vertical to thedirection of inflow, the increase of height will result in an increasing trend for thePM10concentrations on both sides of the building.The investigation results show that type of NE>SE>SW>NW (East-high andwest-low road intersection), type of SW>NE>SE>NW (South-high and north-low roadintersection), and type of WS>EN>ES>WN (Windward crossed-high roadintersections) occupy72.2percent.busy intersection in xi’an.the perennial dominantwind direction is northeasterly in Xi’an, and three typical architectural layouts willform different flow fields (including the vortex) and PM10concentration fields aroundthe traffic intersection. East-high and west-low road intersection will generate twostrong vortexes at the entrance of the downwind street, which makes the PM10accumulating at the vortex centers and very low PM10concentration at the windwardside of the street. South-high and north-low road intersection has single strong vortexin the downwind west street, which causes the PM10accumulation at the center andthe insignificant diffusion of PM10on the leeward side of the street. Windwardcrossed-high road intersections (type of WS>EN>ES>WN) will produce low-intensityvortex in upper wind street (North Street), which will hinder the PM10diffusion in theupper wind streets. However, the PM10concentrations in downwind streets arerelatively low and distributed evenly. In addition, due to the impact of the complexflow field, PM10in north-south streets and PM10in east-west streets will diffuseinteractively at the intersection center, which is liable to exceed the limitation of PM10concentration according to GB criterion.