The influence of vegetation on the horizontal and vertical distribution of pollutants in a street canyon.
The influence of vegetation on the horizontal and vertical distribution of pollutants in a street canyon.
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DOI：
10.1016/j.scitotenv.2012.10.101
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发表时间：
2013-01
期刊：
影响因子：
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通讯作者：
J. Salmond;David E. Williams;G. Laing;Simon Kingham;Kim N. Dirks;I. Longley;G. Henshaw
中科院分区：
文献类型：
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作者：
J. Salmond;David E. Williams;G. Laing;Simon Kingham;Kim N. Dirks;I. Longley;G. Henshaw
城市的空间限制意味着，在现有的城市结构内增加树木密度的机会有限，街道峡谷植被增加的净影响对当地规模的城市空气质量是有利还是不利尚不清楚。本文介绍了在新西兰奥克兰进行的一项实地研究的数据，该研究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，树叶的存在对污染物的迁移有明显的影响，并导致污染物在树顶下方的峡谷中净积累。污染物浓度在时间上局部尖峰的发生率和幅度在树冠本身内减少了。无叶时，污染物浓度随高度变化不显著。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，迎风侧和背风侧之间的差异较小。与之前的模拟研究预测的那样，在开叶期间，背风面的浓度相对于落叶条件下观察到了较小的相对增加。然而，没有观察到迎风侧浓度的预期下降。结果表明，树叶的存在减少了新车尾气的向上输送，增加了污染物在树冠空间内的储存，并减少了清洁空气从高处向下的穿透。观察到的NO和NO2浓度之间的差异不能仅通过扩散过程来解释，这表明大气中的化学成分可能也与树木上树叶的存在有关。
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 NO2concentrations 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.