Abstract
Human health risks caused by PM2.5 raise awareness to the role of trees as bio-filters of urban air pollution, but not all species are equally capable of filtering the air. The objectives of this current study were: (1) to determine the foliar traits for effective PM2.5-capture and (2) explore species-to-species differences in foliar PM2.5-recapture capacity following a rain event. The study concluded that overall, the acicular needle shape made conifers more efficient with PM2.5 accumulation and post-rainfall recapture than broadleaved species. The foliar shape and venation of broadleaved species did not appear to influence the PM2.5 accumulation. However, the number of the grooves and trichomes of broadleaved species were positively related to foliar PM2.5 accumulation, suggesting that they could be used as indicators for the effectiveness of tree PM2.5 capture. Furthermore, the amount of PM2.5 removal by rainfall was determined by the total foliar PM2.5. Not all PM2.5 remained on the foliage. In some species, PM2.5 was resuspended during the growing season, and thus reduced the net particular accumulation for that species. These findings contribute to a better understanding of tree species potential for reducing PM2.5 in urban environments.
Highlights
Summer episodes may increase PM2.5 concentrations due to an increased in the likelihood of stationary air masses[3], intense secondary aerosol formation[4,5,6] and forest fires[7,8,9]
Atmospheric PM2.5 captured on the leaves of urban trees varied among species and seasons (Fig. 1, see Supplementary Table S1)
The four most efficient broadleaved PM2.5-retention species were Catalpa specieosa, Ulmus pumila, Amygdalus triloba and Broussonetta papyrifera, all characterized by leaves covered with dense hairs, whereas the least effective species wereTilia tuan, Armeniaca sibirica and Lonicera maackii, which had smooth leave surfaces
Summary
Summer episodes may increase PM2.5 concentrations due to an increased in the likelihood of stationary air masses[3], intense secondary aerosol formation[4,5,6] and forest fires[7,8,9]. “greening”) has been suggested as one method to reduce PM2.5 in urban areas because these measures would effectively complement air pollution mitigation[10]. Studies conducted in the UK indicated that planting trees on one-fourth of the available urban area can reduce PM10 concentrations by 2 to 10%17. Tree planting can be considered pollution mitigation measure in a variety of urban settings. If urban vegetation is to be employed as a measure for controlling the air pollution, the most efficient species and tree spacing should be used to maximize PM2.5 uptake by vegetation. The ability to identify the most efficient vegetation attributes and species for capturing PM2.5 is important because that will provide a basis for selecting plants to improve air quality in vulnerable areas. Large-scale sampling must be conducted to quantify the relationships between species traits and PM2.5 capturing capacity
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