Impact of Tree Growth Form on Temporal and Spatial Patterns of Particulate Matter with Various Particle Sizes in Urban Street Canyons

Abstract

Abstract Context. Trees reduce street-level particulate matter (PM) pollution in metropolitan areas, thereby enhancing air quality and promoting healthier, more sustainable cities. However, the optimal tree growth type for maximizing the retention of various sizes of PM remains uncertain. Objectives. We aimed to investigate the PM retention abilities of evergreen and deciduous broadleaf street trees. We compared the PM concentration in different seasons and examined the role of leaf phenology in the dispersion of pollutants of different sizes. Methods. We collected data on 6 sizes of PM from 72 sites among 6 streets in Wuhan, China, in summer and winter of 2017-2018. Each street was lined with a single species of either evergreen or deciduous broadleaf trees. Results. We found that concentrations of PM of all sizes were higher in deciduous-lined streets than in evergreen-lined streets, during both summer and winter. for example, 27.2% higher PM2.5 in summer, and 5.5% higher PM10 in winter. However, during summer, evergreen-lined streets had mainly small-sized particles (PM1, PM2.5), which have the potential to infiltrate the human respiratory system, pose greater health risks, while deciduous-lined streets had mainly larger particles (PM4, PM7, PM10, and total suspended particulate [TSP]). During winter, larger particles were dominant, regardless of the tree growth form. Additionally, the disparities in PM concentrations between evergreen- and deciduous-lined streets diminished during winter. Conclusions. We recommend prioritizing evergreen broadleaf trees as the primary street trees while interspersing deciduous broadleaf trees at appropriate intervals. This approach will ensure that urban greenery provides maximum ecological benefits while reducing the PM concentration. The results of this study provide a valuable reference for selecting trees for the targeted reduction of specific-sized PM to support human health through choice of plant growth form.