Relationship between PM2.5 adsorption and leaf surface morphology in ten urban tree species in Shenyang, China

Abstract

ABSTRACTThis study investigated the adsorption of particulate matter with a diameter <2.5 µm (PM2.5) by leaves of ten tree species in Shenyang city. An aerosol generator was used to quantitatively determine PM2.5 adsorption capacity. Atomic force microscopy was used to determine the micro-morphological characteristics of the leaf surface, including roughness parameters and the PM2.5 absorption mechanism of the tree leaves. The results showed a positive correlation between PM2.5 adsorption capacity and PM2.5 concentration during different months: October (0.618 ± 0.16 μg· cm−2) > September (0.514 ± 0.14 μg· cm−2) > July (0.509 ± 0.14 μg· cm−2) > August (0.487 ± 0.12 μg· cm−2) > June (0.464 ± 0.08 μg· cm−2) > May (0.359 ± 0.08 μg· cm−2). PM2.5 absorption capacity was higher on leaves where the folded leaf lamina was covered by fine hairs, as they were rough with many protrusions and fillisters on the leaf surface. The tree species with a smooth leaf surface and low stomatal density and stomatal opening had a weak ability to adsorb PM2.5. The average roughness of the leaves was ranked according to PM2.5 adsorption per unit leaf area, and leaf roughness was significantly correlated with PM2.5 adsorption capacity per unit leaf area (R2 = 0.706). Tree species with a leaf surface morphology that facilitates absorption of PM2.5 and other particles, such as Pinus tabulaeformis and Platycladus orientalis, should be selected to improve the environmental effects of urban forest on air quality.