街区建筑物对城市交通隧道废气排放的影响

采用大气边界层模式和随机游动扩散模式相连接的模拟方法,对上海市拟建的交通隧道排气口附近街道建筑物区域的气流分布和废气排放物浓度场进行了数值模拟分析,设计了6种方案,并按不同的废气排放形式,分别分析了街区的地面污染物质量浓度分布.结果表明,在建筑物存在的情况下,排风口造成的地面污染物质量浓度的最高值会很大,可达0.44 mg/m3,若换成排风塔,则为0.13 mg/m3; 没有建筑物的情况下,由排风口和排风塔造成的地面污染物最高质量浓度分别为0.11 mg/m3,0.4 mg/m3.当风速增大,质量浓度会降低,最大值分别从0.44 mg/m3降为0.2 mg/m3,和从0.13 mg/m3降为0.1mg/m3.分析表明,建筑物附近的气流特征对污染物扩散会起引导作用: 垂直方向上,导致污染物从高空被带入地面; 水平方向上,使得污染物在下风向堆积; 当风速增大时,地面污染物质量浓度值降低.同时研究表明,对排风塔污染物散布起主要作用的是水平方向的气流结构,而对排风口的污染物散布起主要作用的则是其附近建筑物的背风侧的气流下洗效应和水平流场,因此建筑物背风侧有可能成为重污染区.

Effects of buildings in street blocks on the exhaust release of the urban underground traffic tunnels

In this paper, the author has reported his investigation and statistical research based on six schemes and two different types of urban traffic exhaust emission, the air flow and pollutant scattering around the exhaust installations of the traffic tunnels in Shanghai in a random walk diffusion model and an atmospheric boundary layer model. As is known, buildings in the street blocks are of primary importance for the city dwellers' survival and also play a very important role in the exhaust emission of the pollutants. The results of our investigation indicate that the peak values of the surface pollutant concentration caused by the traffic exhaust outlets and towers with the buildings statistically reach 0.44 mg/m3 and 0.13 mg/m3 respectively, as against 0.11 mg/m3 and 0.4 mg/m3 in the places with no buildings. In case the wind speed increases, the peak values of the surface pollutant scattering concentration may decrease from 0.44 mg/m3 to 0.2 mg/m3 and from 0.13 mg/m3 to 0.1 mg/m3 respectively. The results of our investigation also show that the pollutant dispersion can be affected by the air flow around the buildings, e.g. when the air pollutants flow back to the surface vertically and mainly concentrate in the leeward areas in a horizontal plane, the horizontal windward direction would become the most important factor for the pollutant dispersion from the exhaust tower. However, for the exhaust outlets, the downwash flow field in the wake area of the buildings and the horizontal windward areas would play the most important role in the pollutant scattering. Therefore the wake area of the buildings may also become the hardest hurt pollutant-clustered regions.