Lu Kai-Fa, Peng Zhong-Ren
iAdapt: International Center for Adaptation Planning and Design, College of Design, Construction and Planning, University of Florida, PO Box 115706, Gainesville, FL 32611-5706, USA.
iAdapt: International Center for Adaptation Planning and Design, College of Design, Construction and Planning, University of Florida, PO Box 115706, Gainesville, FL 32611-5706, USA.
Sci Total Environ. 2023 Feb 1;858(Pt 1):159902. doi: 10.1016/j.scitotenv.2022.159902. Epub 2022 Oct 31.
Viaduct is a ubiquitous transportation infrastructure in the congested megacities worldwide to improve the accessibility and capacity of urban transportation network. However, there is a lack of understanding of the impacts of the interplay between viaduct-ground emissions and viaduct-canyon configurations on the particle distribution in urban street canyon. To fill the research gap, we conducted vertical measurements of particle number concentrations (PNCs) at different heights of "street canyon along a viaduct" to reveal effect of viaduct on the vertical distribution of PNCs in street canyon. Observation results indicated that the vertical profiles of PNCs exhibited bimodal distribution patterns, which were more significant for coarse particles than fine particles. The one peak appeared at ground level and the other at the viaduct height, indicating the impacts of "double" emission sources (i.e., the emissions on the ground and viaduct) and the hindrance of viaduct to particle diffusion. We further modelled the role of viaduct in street canyon through Computational Fluid Dynamics (CFD) simulations to reveal the vertical distribution of particles under different viaduct-canyon configurations and discern the contributions of viaduct and ground emissions to the particle distribution. Simulation results showed that viaduct changed airflow field and turbulence structure and elevated particle concentrations in street canyon while the optimized viaduct-canyon configurations including higher viaduct height (12 > 10 > 8 m), smaller aspect ratio (0.5 > 0.67 > 1), and shorter centerline distance (0 > 1 > 2 m) between canyon and viaduct could bring better dispersion conditions and lower particle concentrations. Additionally, ground emissions contributed more to the vertical distribution of particles on the leeward side of street canyon than viaduct emissions while the windward side displayed the opposite characteristics to the leeward side. These findings revealed the general patterns of particle diffusion in viaduct-canyon configurations and provided implications into viaduct design and traffic management to alleviate local particulate pollution.
高架桥是全球拥堵大城市中普遍存在的交通基础设施，用于改善城市交通网络的可达性和容量。然而，人们对高架桥地面排放与高架桥峡谷配置之间的相互作用对城市街道峡谷中颗粒物分布的影响缺乏了解。为了填补这一研究空白，我们在“高架桥沿线街道峡谷”的不同高度进行了颗粒物数浓度（PNCs）的垂直测量，以揭示高架桥对街道峡谷中PNCs垂直分布的影响。观测结果表明，PNCs的垂直剖面呈现双峰分布模式，粗颗粒比细颗粒更为显著。一个峰值出现在地面高度，另一个出现在高架桥高度，表明“双重”排放源（即地面和高架桥上的排放）的影响以及高架桥对颗粒物扩散的阻碍。我们进一步通过计算流体动力学（CFD）模拟对高架桥在街道峡谷中的作用进行建模，以揭示不同高架桥峡谷配置下颗粒物的垂直分布，并识别高架桥和地面排放对颗粒物分布的贡献。模拟结果表明，高架桥改变了气流场和湍流结构，提高了街道峡谷中的颗粒物浓度，而优化的高架桥峡谷配置，包括更高的高架桥高度（12>10>8米）、更小的长宽比（0.5>0.67>1）以及峡谷与高架桥之间更短的中心线距离（0>1>2米），可以带来更好的扩散条件和更低的颗粒物浓度。此外，地面排放在街道峡谷背风侧对颗粒物垂直分布的贡献比高架桥排放更大，而迎风侧则呈现出与背风侧相反的特征。这些发现揭示了高架桥峡谷配置中颗粒物扩散的一般模式，并为高架桥设计和交通管理提供了减轻局部颗粒物污染的启示。
