The variation in the amount of black carbon particles deposited on leaves at different positions in the canopy of mature Cornus florida and related factors.

In urban areas, black carbon (BC) particles with an aerodynamic diameter of 2.5 µm or less (PM) have adverse effects on human health. Urban greening is considered a potential solution to mitigate air pollution caused by BC particles, because atmospheric BC particles can be deposited and retained on the leaves of urban greening trees, resulting in a reduction in the atmospheric concentration of BC particles around the trees. However, there is no information on the variation in the amount of BC particles deposited on leaves at different positions in the canopy of mature urban greening trees throughout a year, its related factors, and the amount of BC particles on the entire canopy of a mature tree. The objective of this study was to investigate the amount of BC particles deposited on the leaves of mature trees of Cornus florida L. at different positions in the canopy and its related factors. The results indicated that there were significant differences in the amount of BC particles among leaf positions in June and July 2020. In and after July, a positive correlation was observed between the amount of BC particles deposited on the leaves and leaf surface traits, such as the amount of epicuticular wax. Consequently, the capacity to remove atmospheric BC particles varies with leaf position in the canopy of mature urban greening trees, primarily attributable to the variations in leaf surface traits. In addition, when the variation in the amount of BC particles deposited on leaves at different leaf positions in the canopy does not take into account, the total amount of BC particles in the entire canopy of a mature C. florida tree is 0.7-33% higher than the present assessment method, which takes this variation into account. This difference should be considered when assessing the overall BC removal ability of the entire canopy in mature urban greening trees.