Seasonal variations in leaf capturing of particulate matter, surface wettability and micromorphology in urban tree species

The seasonal changes in leaf particulate matter （PM） accumulation, surface wettability and micromor- phology in urban tree species, including Sophorajaponica （S. japonica）, Platanus acerifolia （P. acerifolia） and Cedrus deodara （C. deodara）, were studied during a single growing season. The three species showed distinct seasonal trends in PM accumulation, increasing from spring to autumn （or winter） even during the rainy season, but at different rates. During the study, the leaf PM retention amount ofP acerifolia, a species with ridged leaf surfaces, was significantly higher than that of S. japonica and C. deodara, species with waxy leaf surfaces. The contact angles of water droplets on leaves decreased with leafage except on the abaxial surface orS.japonica, which remained non-wettable or highly non-wettable throughout the growing season; the decrease in the contact angle on adaxial surface of S. japonica was greater when compared with P acerifolia and C. deodara. A significant and negative relationship existed between leaf PM retention amounts and contact angles on adaxial surface of leaves of all three species. The increase in wettability, probably caused when epicuticular wax was destroyed by mechan- ical and chemical abrasion, seemed to be the main factor leading to seasonal variations in leaf PM accumulation.