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Integrated impacts of tree planting and street aspect ratios on CO dispersion and personal exposure in full-scale street canyons
Sun Yat-sen University.
Sun Yat-sen University.
Sun Yat-sen University.
University of Salento.
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2020 (Engelska)Ingår i: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 169, artikel-id 106529Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Validated by experimental data, this paper performs computational fluid dynamics (CFD) simulations to investigate the influence of tree plantings on urban airflow and vehicular CO exposure in two-dimensional (2D) street canyons with various aspect ratios (building height/street width, AR = H/W = 0.5, 1, 3, 5) and ground-level source. The impacts of tree canopy bottom height (Htb = 2 m, 6 m), tree stand density (y-density = 0.33, 0.67, 1) and leaf area density (LAD = 0.5, 1, 2 m2/m3) are considered. Personal intake fraction (P_IF) and its spatial mean value in leeward and windward sides (<P_IF>lee, <P_IF>wind) and for entire streets (street intake fraction, <P_IF>) are adopted to assess overall pollutant exposure. For cases without trees, only one main vortex exists in shallow streets with AR = 0.5-3 and <P_IF> as AR = 3 (5.80 ppm) slightly exceeds AR = 0.5-1 (3.98-3.84 ppm). However, two counter-rotating vortexes appear in deep streets (AR = 5), inducing 1-2 orders smaller pedestrian-level velocity (U/Uref~10−4-10−3) and one-order greater <P_IF> (46.80 ppm) than shallow streets. Trees always weaken wind in streets and raise <P_IF> more in shallower streets by 46.0% as AR = 0.5 (3.98 ppm-5.81 ppm), 26.0-45.9% as AR = 1 (3.84 ppm to 4.84-5.60 ppm), 16.2-50.3% as AR = 3 (5.80 ppm to 6.74-8.72 ppm), but only 8.5-23.4% as AR = 5 (46.80 ppm to 50.78-57.73 ppm). Particularly, as AR = 1, trees raise <P_IF>lee (5.87 ppm) by 27.1-57.2%, while <P_IF>wind (1.80 ppm) only by 0%-23.3%. Higher Htb, smaller y-density or LAD produce less increase of <P_IF>. As AR = 3, vegetation increases <P_IF>lee (8.84 ppm) by 21.2%-66.4% but little affects <P_IF>wind (2.76 ppm). Lower Htb produces smaller <P_IF> differing from AR = 1. As AR = 5, vegetation increases <P_IF>wind (63.97 ppm) by 15.1-36.6% but reduces <P_IF>lee (29.63 ppm) by 5.2-8.5%. Although further investigations are still required for design purpose, this paper provides effective methodologies to quantify how vegetation influences street-scale pollutant exposure.

Ort, förlag, år, upplaga, sidor
2020. Vol. 169, artikel-id 106529
Nyckelord [en]
Computational fluid dynamic (CFD) simulation, Personal intake fraction (P_IF), Pollutant dispersion, Porous medium, Street aspect ratio (H/W, AR), Urban vegetation
Nationell ämneskategori
Samhällsbyggnadsteknik
Identifikatorer
URN: urn:nbn:se:hig:diva-31170DOI: 10.1016/j.buildenv.2019.106529Scopus ID: 2-s2.0-85075528720OAI: oai:DiVA.org:hig-31170DiVA, id: diva2:1374995
Tillgänglig från: 2019-12-03 Skapad: 2019-12-03 Senast uppdaterad: 2019-12-03Bibliografiskt granskad

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