Urban forest as a strategy of particulate matter (PM) capture and retention

The significant trend of urbanization is accompanied by a range of serious issues, as air pollution, which is one of the prevalent health problems in numerous countries globally. Particulate matter (PM), is recognized as the foremost pollutants of concern for its adverse effects on human health and the environment. Urban vegetation represents a powerful ally in the fight against air pollution, since plants play a crucial role in capturing and mitigating the impact of PM in the atmosphere. However, the capability of PM adsorption by vegetation depends on a lot of factors, including leaf shape, surface wettability and leaf epidermal features, i.e. cuticular striations and epicuticular waxes. Moreover, the deposition process is affected by the canopy characteristics, wind speed, particle size. This study has evaluated the particle capture efficiencies of four broadleaved species (Celtis australis, Fraxinus ornus, Morus alba and Tilia cordata) settled as urban forest within a green area in the city of Reggio Emilia, Italy. The airborne particles have been studied through SEM/x-EDS analysis from a quantitative and chemical composition point of view, verifying the role played by leaf micromorphology in the efficiency to intercept PM. The data have been collected on leaves coming from 2 different seasons (spring and autumn) during 3 following years. Results show that F. ornus and C. australis have captured significantly more particles per unit area than M. alba and T. cordata. Leaf micromorphology proved to be important, however it was no possible to identify a micromorphological trait more influential than others in determining the ability of the species to capture PM. In general, PM trapped by these species was rich in non-toxic or low-toxic compounds, even if in small quantities, like Ni, Cr and Ba. This, along with the fact that these species have largely collected fine particles, has proved the fundamental role of urban vegetation in PM capture and detainment.