Abstract
A number of studies have focused on the capacity of urban trees and shrubs to serve as efficient biological filters to mitigate air pollution. In this study, five different tree species were assessed for this function. Kerria japonica, Sophora japonica, Philadelphus pekinensis, Gleditsia sinensis, and Prunus persica 'Atropurpurea' were tested in a deposition chamber using (NH4)2SO4 particles. We quantified and compared the capability of all tested trees to remove particles by assessing deposition velocity, a measure of the ability to remove particles. When placed in the deposition chamber, S. japonica had the greatest deposition velocity, followed by Philadelphus pekinensis, G. sinensis, Prunus persica 'Atropurpurea,' and K. japonica, in descending order. In addition, the comparison of deposition velocities among these species suggested that certain leaf geometries and surface characteristics of broadleaf trees, such as trichomes and grooves, increased particle capture. However, these results change under a different simulation condition using ambient air, suggesting that some trees actually increase pollutant number concentrations more than reduce particle concentration. This outcome can be explained by the aerodynamic effect of trees exceeding the filtering capacity of vegetation under some conditions. This highlights the difficulty of generalizing species selection criteria for practice use. Accordingly, our results indicate that using vegetation to reduce particle pollution and improve the air quality is not a universally advisable and viable solution.
Highlights
Since 2012, many cities in China have been experiencing severe and persistent haze pollution events, affecting 1.3 million km2 and 800 million people [1]
Vd values changed with the aerosol flowrate; for each tree species, higher flowrates achieved higher deposition velocities, confirming the trend of enhanced particle deposition occurring at higher wind speeds, as reported by Ould-Dada et al [16], Freer-Smith et al [17], and Beckett et al [24]
Wind speed had a greater influence on Vd for both leaves and stems than capture efficiency (Cp); this was because Cp values are relatively small for stems and show a weaker relationship with wind speed
Summary
Since 2012, many cities in China have been experiencing severe and persistent haze pollution events, affecting 1.3 million km and 800 million people [1]. Ash haze appears when air pollution intensifies, seriously affecting people’s lives and presenting elevated health concerns. Acute pollution leads to many adverse physical reactions and diseases. Global incidences of alveolar inflammation, respiratory-tract infections, and acute cardiovascular disorders have significantly increased over the past few decades [2,3,4,5].
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