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The influence of vegetation on the horizontal and vertical distribution of pollutants in a street canyon

机译：植被对街道峡谷污染物水平和垂直分布的影响

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摘要

Space constraints in cities mean that there are only limited opportunities for increasing tree density within existing urban fabric and it is unclear whether the net effect of increased vegetation in street canyons is beneficial or detrimental to urban air quality at local scales. This paper presents data from a field study undertaken in Auckland, New Zealand designed to determine the local impact of a deciduous tree canopy on the distribution of the oxides of nitrogen within a street canyon. The results showed that the presence of leaves on the trees had a marked impact on the transport of pollutants and led to a net accumulation of pollutants in the canyon below the tree tops. The incidence and magnitude of temporally localised spikes in pollutant concentration were reduced within the tree canopy itself. A significant difference in pollutant concentrations with height was not observed when leaves were absent. Analysis of the trends in concentration associated with different wind directions showed a smaller difference between windward and leeward sides when leaves were on the trees. A small relative increase in concentrations on the leeward side was observed during leaf-on relative to leaf-off conditions as predicted by previous modelling studies. However the expected reduction in concentrations on the windward side was not observed. The results suggest that the presence of leaves on the trees reduces the upwards transport of fresh vehicle emissions, increases the storage of pollutants within the canopy space and reduces the penetration of clean air downwards from aloft. Differences observed between NO and NO_2 concentrations could not be accounted for by dispersion processes alone, suggesting that there may also be some changes in the chemistry of the atmosphere associated with the presence of leaves on the trees.
机译：城市的空间限制意味着在现有的城市结构中增加树木密度的机会有限，并且尚不清楚街道峡谷中植被增加的净效应是有利于还是不利于地方尺度上的城市空气质量。本文提供了在新西兰奥克兰进行的一项现场研究的数据，旨在确定落叶树冠对街道峡谷内氮氧化物分布的局部影响。结果表明，树木上的叶子的存在对污染物的运输有显着影响，并导致树木顶部下方峡谷中污染物的净积累。在树冠本身内，污染物浓度的时间局部性峰值的发生率和大小均得到降低。缺叶时未观察到污染物浓度随高度的显着差异。对与不同风向相关的浓度趋势的分析表明，当树叶在树上时，迎风面和背风面之间的差异较小。如先前的建模研究所预测的，在叶上期间相对于叶下条件下，观察到背风侧浓度的相对增加较小。然而，未观察到预期的迎风侧浓度降低。结果表明，树木上的叶子减少了新鲜车辆排放物的向上运输，增加了树冠空间内污染物的存储，并减少了清洁空气从高处向下的渗透。仅通过分散过程无法解释NO和NO_2浓度之间的差异，这表明与树木上存在叶子相关的大气化学也可能会发生一些变化。

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  • 来源
    《Science of the total environment》 |2013年第15期|287-298|共12页
  • 作者

    J.A Salmond; D.E. Williams; G. Laing; S. Kingham; K. Dirks; I. Longley; G.S. Henshaw;

  • 作者单位

    School of Environment, University of Auckland, Private Bag 92019, Auckland 1142. New Zealand;

    Department of Chemistry, The University of Auckland, Auckland, New Zealand;

    Aeroqual Ltd, 109 Valley Rd, Mr Eden, Auckland, New Zealand;

    Department of Geography, The University of Canterbury, Christchurch, New Zealand;

    Faculty of Medical and Health Sciences, The University of Auckland, Auckland, New Zealand;

    National Institute of Water and Atmospheric Research, Auckland 1149, New Zealand;

    Aeroqual Ltd, 109 Valley Rd, Mr Eden, Auckland, New Zealand;

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  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

    vegetation; street canyon; nitrogen dioxide; trees; air quality;

    机译：植被;街头峡谷二氧化氮;树木;空气质量;

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