Influence of Viaducts on Dispersion of Air Particles in Street Canyons

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1 Research of Environmental Sciences Vol 25 No 2 Feb 2012 J ZHANG Chuanfu ZENG Jianrong WEN Mou et al Influence of viaducts on dispersion of air particles in street canyons J Research of Environmental Sciences * CFD 3 H W k-ε H W CFD X513 A Influence of Viaducts on Dispersion of Air Particles in Street Canyons ZHANG Chuan-fu 1 ZENG Jian-rong 1 WEN Mou 2 ZHANG Gui-lin 1 FANG Hai-ping 1 LI Yan 1 1 Key Laboratory of Nuclear Analysis Techniques Shanghai Institute of Applied Physics Chinese Academy of Sciences Shanghai China 2 Shanghai Institute of Applied Mathematics and Mechanics Shanghai University Shanghai China Abstract Due to the increase of private vehicles in cities in China high-level pollution is often detected in urban street canyons Using a two-dimensional computational fluid dynamics CFD model the environmental impacts of viaducts on the wind flow and dispersion of particles were studied under three different height width ratios H W of street canyons Two-dimensional flow and dispersion of particles from traffic exhaust were modeled using the standard k-ε turbulence and discrete phase models The results revealed that increasing the H W effectively raised the particle concentration and mean particle residence time The airflows were obviously disturbed at the region around the viaduct whereas there was no significant change of the airflows near the walls of the buildings the ground and the roofs of the canyon The particle concentration at the lower part of the walls increases when a viaduct exists in the street canyons Key words street canyons viaduct particle dispersion CFD 1-4 ρ PM 10 ρ PM 2 5 ρ PM μg m KJCX3 - SYW - N zcf0225@ 126 com * 0 51% 0 68% ly@ sinap ac cn 7-8 ρ PM μg m 3 4% 3% 2% 5-6 PM μm

2 ε + U ε 9-10 j = ν t x CFD 3 20 a t x j x j x j CFD ε U i C k ε1 ν t + U U j i - C x j x x ε2 ε 2 i j XIE 11 k-ε x i y i i j U i U j RNG k-ε i j i j = 1 2 t k ε ν 12 AHMADI 13 t = C μ k 2 ε C μ = 0 09 C ε1 = 1 44 C ε2 = 1 92 σ 14 k = 1 0 σ ε = KUMAR ~ nm nm CFD du p = F dt D u - u p + g ρ p - ρ + F a 3 ρ 19 p u p u ρ p ρ F D g F a u = u 珔 + u' u珔 k-ε 53 2 km u' Fluent 1 CO F KONDO 25 drag Stokes NO x 18μ F drag = F D u - u p = u - u ρ p d 2 p 4 p C c CFD d p μ C c Stokes Cunningham 3 1 dx dt = u p N Navier-Stokes N = k-ε k-ε Σ n i dt i i n i i dt i k t + k U j = x j x j ν t k ( σ k x ) j U ( ) i U i + ν t + U j x j xi x j - ε 1 ( ) σ ε [ ( ) ] 2 1 +

3 Fig 1 Schematic diagram of street canyon with a viaduct 3 m s H W H W H W W 20 m H W 1 2 w 12 m h 5 m = 0 01W x min y min = 0 01H Fig 2 The wind stream lines in a street canyon 3 2 m 60% x ± 1 ± 3 ± 5 m y 0 3 ~ 1 1

4 K = CU H HL Q Q 6 K C A K B U H H L Q Q A K 27 3 A H W 0 5 K B K A K 3 K 2 5 μm K H W A K H W C c 0 01 ~ 10 μm 4 10 μm 300 nm 1% K 0 1 μm Fig 4 Distributions of particles numbers at wall in street canyons μm H W 0 5 K A Fig 3 Distributions of particles numbers with different size at wall A in street canyon with H W = 0 5 K GROMKE 5 A H W 0 5 A K H W 1 2 A K A A A B Fig 5 Influence of a viaduct on the distribution 4 K particles numbers at wall A

5 2 163 K K on health J Sci Total Environ POPE Ⅲ C A H W cardiac and pulmonary health risks J C e T Environ C t = C 0 e - t T 7 canyons J Atmos Environ C t t H W street canyon J 303 ± ± ± 19 s of concentration fluctuations in an urban street canyon J H W 2 Environ H W a 2 5 μm canyon J Building and Environment AHMADI G b deposition near a small isolated building J Engineering and Industrial Aerodynamics c J H W 15 KUMAR P FENNELL P d A canyon J Sci Total Environ KUMAR P FENNELL P References 1 DOCKERY D POPE C Acute respiratory effects of particulate air pollution J Annual Review of Public Health ANDERSON K AVOL E EDWARDS S et al Controlled exposures of volunteers to respirable carbon and sulfuric acid aerosols J J Air Waste Manage Assoc SCHWARTZ J DOCKERY D NEAS L Is daily mortality associated specifically with fine particles J J Air Waste Manage Assoc HARRISON R YIN Jianxin Particulate matter in the atmosphere which particle properties are important for its effects DOCKERY D Health effects of fine particulate air pollution lines that connect J J Air Waste Manage Assoc BRUGGE D DURANT J RIOUX C Near-highway pollutants in motor vehicle exhaust a review of epidemiologic evidence of Environmental Health 7 VARDOULAKIS S FISHER B E A PERICLEOUS K et al Modelling air quality in street canyons a review J Atmos 8 LI Xianxiang LIU Chunho LEUNG D et al Recent progress in CFD modelling of wind field and pollutant transport in street GARCIA SAGRADO A VAN BEECK J RAMBAUD P et al Numerical and experimental modelling of pollutant dispersion in a Journal of Wind Engineering and Industrial Aerodynamics PAVAGEAU M SCHATZMANN M Wind tunnel measurements Atmos 11 XIE Xiaomin HUANG Zhen WANG Jiasong Impact of building configuration on air quality in street canyon J Atmos Environ XIE Xiaomin HUANG Zhen WANG Jiasong et al The impact of solar radiation and street layout on pollutant dispersion in street LI A Computer simulation of particle transport and Journal of Wind BRITTER R Measurements of particles in the nm range close to road level in an urban street BRITTER R Effect of wind direction and speed on the dispersion of nucleation and accumulation mode particles in an urban street canyon J Sci Total Environ KUMAR P GARMORY A KETZEL M et al Comparative study of measured and modelled number concentrations of nanoparticles in an urban street canyon J Atmos Environ J J

6 J YASSIN M F KELLNEROV R JAŇOUR Z Impact of street intersections on air quality in an urban environment J Atmos Environ SOULHAC L GARBERO V SALIZZONI P et al Flow and dispersion in street intersections J Atmos Environ urban street canyon J Atmos Environ J KUMAR P FENNELL P BRITTER R Measurements of particles J in the nm range close to road level in an urban street 25 KONDO H TOMIZUKA T A numerical experiment of roadside diffusion under traffic-produced flow and turbulence J Atmos Environ OKE T Street design and urban canopy layer climate J Energy and Buildings GREEN N ETHERIDGE D RIFFAT S Location of air intakes to avoid contamination of indoor air a wind tunnel investigation J Building and Environment KUMAR P FENNELL P LANGLEY D et al Pseudosimultaneous measurements for the vertical variation of coarse fine and ultrafine particles in an urban street canyon J Atmos Environ WEBER S KUTTLER W WEBER K Flow characteristics and particle mass and number concentration variability within a busy canyon J Sci Total Environ GROMKE C BUCCOLIERI R DI SABATINO S et al Dispersion study in a street canyon with tree planting by means of wind tunnel and numerical investigations-evaluation of CFD data with experimental data J Atmos Environ

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