Numerical studies of passive and reactive pollutant dispersion in high-density urban models with various building densities and height variations. (15th June 2020)

• Record Type: Journal Article
• Authors: Zhang, Yong; Ou, Cuiyun; Chen, Lan; Wu, Luolin; Liu, Jiarui; Wang, Xuemei; Lin, Hualiang; Gao, Peng; Hang, Jian
• Is Part Of: Building and environment. Volume 177(2020)
• Publication Date: 2020-06-15
• Subjects: NO–NO2–O3 photochemistry -- Vehicular pollutant dispersion -- Personal intake fraction (P_iF) -- Computational fluid dynamic (CFD) -- Building packing density -- High-density urban models; Buildings -- Environmental engineering -- Periodicals; Building -- Research -- Periodicals; Constructions -- Technique de l'environnement -- Périodiques; Electronic journals; 696
• DOI: 10.1016/j.buildenv.2020.106916
• Languages: English
• ISSNs: 0360-1323

Abstract

Abstract: Vehicular pollutant exposure in the near-road buildings of high-density urban areas has been rarely studied. This paper investigates the impacts of high-density building morphology on passive (CO) and reactive (NOx -O3 ) pollutant dispersion in three-dimensional (3D) urban-like models, e.g. medium (street width W = 30 m, λ p = 0.25, λ f = 0.6) and compact ( W = 18 m, λ p = 0.39, λ f = 0.94) layouts with uniform ( H = 72 m) or various heights ( H 1 = 48 m, H 2 = 96 m). Personal intake fraction P_iF and its spatially-averaged value for the entire building wall (< P_iF >W ) are utilized for exposure assessment. Some meaningful findings are proposed: 1) When wind blows through neighborhood-scale (~1 km) urban models, it decelerates rapidly and then reaches a flow balance where pedestrian-level velocity and pollutant exposure vary depending on building densities and height variations. 2) Uniform-height cases attain overall W of ~0.3–1.3 ppm in target streets. The compact layout ( λ f = 0.94) experiences weaker vertical exchange where downward helical flows transport more pollutants to windward wall than medium-type ( λ f = 0.6), inducing two-order larger windward-side W (~1 ppm) than leeward-side (~0.01 ppm). 3) Building height variations obtain greater velocity and smaller W (~0.2–1.0 ppm) in front of taller buildings than those behind them ( W ~2.6–4.2 ppm). 4) No matter with or without height variations, densifying building arrays ( λ f = 0.6 to 0.94) raises windward-side W and mitigates leeward-side W, but overall W for both sides of target streets only change slightly. 5) With present NOx -O3 photochemistry (source emissions NO:NO2 = 10:1, background [O3 ] = 20 ppbv), NO2 exposure is 40%–230% larger than passive CO exposure, but NO is near to CO. This study implies the near-road pollutant exposure in high-density urban models is sensitive to building morphology which should be carefully designed. Highlights: Vehicular pollutant dispersion in 3D high-density urban models is studied by CFD. Averaged personal intake fraction P_iF for entire building wall (< P_iF >W ) is used. Compact layout ( λ f = 0.94) obtains two-order greater windward < P_iF >W than leeward. Height variations attain weaker wind and larger < P_iF >W behind taller building. NOx -O3 reactions induce ~200% rise of NO2 exposure but little affect NO exposure.