City breathability and its link to pollutant concentration distribution within urban-like geometries

Buccolieri, Riccardo; Sandberg, Mats; Sabatino, Silvana Di

doi:10.1016/j.atmosenv.2010.02.022

Cited by 263 publications

(146 citation statements)

References 33 publications

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“…Recently, research has been undertaken to study dispersion and ventilation in actual or generic building block arrays with tree-free streets (e.g. Boppana et al, 2010;Borrego et al, 2006Borrego et al, , 2003Buccolieri et al, 2010;Carpentieri et al, 2012;Di Sabatino et al, 2007;Garbero et al, 2010;Hamlyn et al, 2007;Hang et al, 2011;Panagiotou et al, 2013;Pascheke et al, 2008;Princevac et al, 2010;Ramponi et al, 2014;Soulhac et al, 2012Soulhac et al, , 2011Soulhac et al, , 2003Xie and Castro, 2009). It is evident that such study areas provide a more relevant description of the effects of trees on flow and pollutant dispersion than those with isolated street canyons or intersections.…”

Section: Introductionmentioning

confidence: 99%

Influence of avenue-trees on air quality at the urban neighborhood scale. Part II: Traffic pollutant concentrations at pedestrian level

Gromke

Blocken

2015

Environmental Pollution

139

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a b s t r a c tFlow and dispersion of traffic-emitted pollutants were studied in a generic urban neighborhood for various avenue-tree layouts by employing 3D steady RANS simulations with the realizable k-ε turbulence model. In comparison to the tree-free situation quantitative and qualitative changes with flow reversal in the wind field were observed. Low to moderate increases (<13.2%) in the neighborhood-averaged pollutant concentration were found at pedestrian level. An approximately 1% increase in the neighborhood-averaged concentration was obtained with each percent of the street canyon volumes being occupied by vegetation for occupation fractions between 4 and 14%. The overall pattern of concentration changes relative to the tree-free situation was similar for all avenue-tree layouts. However, pronounced locally restricted decreases or increases in concentration (À87 to þ1378%) occurred. The results indicate the necessity to account for existing or planned avenue-trees in neighborhood scale dispersion studies. Their consideration is prerequisite for reliable urban air quality assessment.

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Section: Introductionmentioning

confidence: 99%

Influence of avenue-trees on air quality at the urban neighborhood scale. Part II: Traffic pollutant concentrations at pedestrian level

Gromke

Blocken

2015

Environmental Pollution

139

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“…Overall, Fig. 10 shows two types of recirculation zones: weak and strong recirculation zones (Buccolieri et al, 2010). The weak recirculation zones, which had a positive normalized horizontal velocity rate, in models b and c did not change the flow direction.…”

Section: Mechanism Of Particle Transportmentioning

confidence: 99%

“…The interaction between an approaching atmospheric flow and a city results in complicated flow patterns between buildings, along streets. An air mass approaching a city can either enter the streets, flow above buildings, or around buildings (Buccolieri et al, 2010). As shown in Fig.…”

Section: Air Flow Streamline and Velocity Vector In The Street Canyonmentioning

confidence: 99%

Evaluating Dust Particle Transport Performance within Urban Street Canyons with Different Building Heights

Mercola

Deng

et al. 2016

Aerosol Air Qual. Res.

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In developing cities, buildings with different heights obstruct the diffusion of pollutants. In this study, dust particles transported within urban street canyons were simulated using Reynolds-averaged Navier-Stokes (RANS) method, and airsolid two-phase flow fields were obtained on a regional scale. Four typical street building models were used in this study: (a) low-rise buildings (H/b = 1), (b) step-up building arrangements (H/b = 1, 2, 3, 4, 5), (c) step-down building arrangement (H/b = 5, 4, 3, 2, 1), and (d) high-rise buildings (H/b = 5). The particle volume fraction distribution in the four models reflected the basic properties of particle transportation in the canyons. Vortices were observed on the roofs of street canyons, which prevented particles from being transmitted into the canyons, and the vortex regions were characterized as low particle concentration.To evaluate the dust particle transport performance in the models, three indices, namely particle transport efficiency, suspension fraction and suspension density, were defined. These concepts were based on the particle number concentrations, which were obtained using the Lagrange approach. The high-rise building model (H/b = 5) demonstrated the lowest transport efficiency among all four models, and it also had the lowest suspension density in the street canyons. This implied that the high-rise buildings hindered the particles from being transporting further and that the particles could not enter the deep canyons easily. In the step-down building arrangement model (H/b = 5, 4, 3, 2, 1), the particle concentration level and suspension density in the canyons were lower than those observed in the step-up building arrangement model (H/b = 1, 2, 3, 4, 5), indicating that a step-down building height arrangement is appropriate for creating construction plans for developing cities.Finally, the variation of the streamwise air velocity, vertical velocity and fluctuating velocity on the roof of canyons along the x direction were separately examined. Notably, the fluctuating velocity was the dominant mechanism of the particle suspension in the canyons.

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“…For instance, canyon aspect (height-to-width) ratio has been identified as one of the most important parameters in categorizing the flow field inside an urban street canyon [5][6][7]. Additionally, the drag coefficient and flow field in the urban canopy layer are strongly dominated by the urban packing density [18,22,23] and the layout of building arrays [24,25]. These studies also demonstrated that the geometrical inhomogeneity in urban design (e.g., building configurations and variability of street width) significantly modifies the local ventilation capacity, and Hang et al [7] showed that height variability determines the momentum flux as well as the removal of pedestrian-level pollutants in urban street canyons.…”

Section: Introductionmentioning

confidence: 99%

“…Accordingly, improving ventilation in street canyons is instrumental for achieving a low-energy urban design [16]. Lastly, with the increased rate of emissions in urban areas, air quality in street canyons and city breathability for urban dwellers are closely tied to the efficiency of the city to ventilate itself [17][18][19][20][21]. Therefore, it is paramount that we evaluate the methods of enhancing wind speed in urban street canyons.…”

Section: Introductionmentioning

confidence: 99%

Pedestrian-Level Urban Wind Flow Enhancement with Wind Catchers

2017

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Dense urban areas restrict air movement, causing airflow in urban street canyons to be much lower than the flow above buildings. Boosting near-ground wind speed can enhance thermal comfort in warm climates by increasing skin convective heat transfer. We explored the potential of a wind catcher to direct atmospheric wind into urban street canyons. We arranged scaled-down models of buildings with a wind catcher prototype in a water channel to simulate flow across two-dimensional urban street canyons. Velocity profiles were measured with Acoustic Doppler Velocimeters. Experiments showed that a wind catcher enhances pedestrian-level wind speed in the target canyon by 2.5 times. The flow enhancement is local to the target canyon with little effect in other canyons. With reversed flow direction, a "reversed wind catcher" has no effect in the target canyon but reduces the flow in the immediate downstream canyon. The reversed wind catcher exhibits a similar blockage effect of a tall building amid an array of lower buildings. Next, we validated Computational Fluid Dynamics (CFD) simulations of all cases with experiments and extended the study to reveal impacts on three-dimensional ensembles of buildings. A wind catcher with closed sidewalls enhances maximum pedestrian-level wind speed in three-dimensional canyons by four times. Our results encourage better designs of wind catchers to increase wind speed in targeted areas.

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City breathability and its link to pollutant concentration distribution within urban-like geometries

Cited by 263 publications

References 33 publications

Influence of avenue-trees on air quality at the urban neighborhood scale. Part II: Traffic pollutant concentrations at pedestrian level

Influence of avenue-trees on air quality at the urban neighborhood scale. Part II: Traffic pollutant concentrations at pedestrian level

Evaluating Dust Particle Transport Performance within Urban Street Canyons with Different Building Heights

Pedestrian-Level Urban Wind Flow Enhancement with Wind Catchers

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