期刊
BUILDING AND ENVIRONMENT
卷 169, 期 -, 页码 -出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.buildenv.2019.106529
关键词
Urban vegetation; Street aspect ratio (H/W, AR); Pollutant dispersion; Personal intake fraction (P_IF); Computational fluid dynamic (CFD) simulation; Porous medium
资金
- National Key R&D Program of China [2016YFC0202206, 2016YFC0202205, 2016YFC0202204]
- National Natural Science Foundation-Outstanding Youth Foundation [41622502]
- STINT [CH2017-7271]
- National Natural Science Foundation of China [51811530017, 41875015]
- Key projects of Guangdong Natural Science Foundation [2018B030311068]
- National Supercomputer center in Guangzhou, P.R. China
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 m(2)/m(3)) are considered. Personal intake fraction (P_IF) and its spatial mean value in leeward and windward sides ((lee), (wind)) and for entire streets (street intake fraction, ) 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 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/Uref10 4-10 3) and one-order greater (46.80 ppm) than shallow streets. Trees always weaken wind in streets and raise 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 50.7857.73 ppm). Particularly, as AR = 1, trees raise (lee) (5.87 ppm) by 27.1-57.2%, while (wind) (1.80 ppm) only by 0%-23.3%. Higher Htb, smaller y-density or LAD produce less increase of . As AR = 3, vegetation increases (lee) (8.84 ppm) by 21.2%-66.4% but little affects (wind) (2.76 ppm). Lower Htb produces smaller differing from AR = 1. As AR = 5, vegetation increases (wind) (63.97 ppm) by 15.1-36.6% but reduces (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.
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