Understanding Particulate Matter Retention and Wash-Off during Rainfall in Relation to Leaf Traits of Urban Forest Tree Species

Abstract

Dynamic particulate matter (PM) behavior on leaves depends on rainfall events, leaf structural and physical properties, and individual tree crowns in urban forests. To address this dependency, we compared the observed relationships between PM wash-off ability and leaf traits on inner and outer crown-positioned leaves during rainfall events. Data showed significant differences in the PM wash-off ability between inner and outer crown-positioned leaves relative to rainfall events due to leaf macro- and micro-structure and geometric properties among tree species. Our results showed that PM wash-off effects on leaf surfaces were negatively associated with trichome density and size of leaf micro-scale during rainfall events. Specifically, Quercus acutissima with dense trichomes and micro-level surface roughness with narrow grooves on leaf surfaces showed lower total PM wash-off in both inner (−38%) and outer (105%) crowns during rainfall. Thus, their rough leaves in the inner crown might newly capture and/or retain more PM than smooth leaves even under rainfall conditions. More importantly, Euonymus japonicus, with a thin film-like wax coverage without trichome, led to higher total PM wash-off in both inner (368%) and outer (629%) crowns during rainfall. Furthermore, we studied the changes in PM wash-off during rainfall events by comparing particle size fractions, revealing a very significant association with macro-scale, micro-scale, and geometric features.

Physicochemical Assessment of the Road Vehicle Traffic Pollution Impact on the Urban Environment

“…These PMs combined with dangerous organic compounds may affect environmental aspects, such as climate change, the greenhouse effect, thinning of the ozone layer due to their toxic effect on the plants and tree leaves, which further affects the oxygen balance in the local atmosphere [12,13]. Mammals are also very exposed to the risk due to contaminated PM penetration into the respiratory system causing respiratory diseases, such as asthma and silicosis [14,15], pulmonary cancer [16,17], and cardiovascular diseases [18,19], which induce long-time illness until death.…”