Relationship between retention PM2.5 and leaf surface AFM character of six greening trees during autumn in Beijing West Mountain.

Abstract

This study investigated PM2.5 adsorption by leaves of six tree species (Pinus bungeana, Pinus tabuliformis, Salix babylonica, Acer mono, Ginkgo biloba, Populus davidiana) in the West Mountain of Beijing. An aerosol generator was used for quantitative determination of PM2.5 adsorption. Atomic force microscopy (AFM) was used to determine micro morphology characteristics on the leaf surface, including roughness parameters and the PM2.5 absorption mechanism of tree leaves. The results showed that the PM2.5 adsorption capacity per unit leaf area was as follows: P. bungeana (2.44±0.22 μg·cm-2) > P. tabuliformis (2.40±0.23 μg·cm-2) > S. babylonica (1.62±0.09 μg·cm-2) > A. mono (1.23±0.01 μg·cm-2) > G. biloba (1.00±0.07 μg·cm-2) > P. davi-diana (0.97±0.03 μg·cm-2). In autumn, PM2.5 adsorption capacity per unit leaf area was as follows: November (2.33±0.43 μg·cm-2) > October (1.62±0.64 μg·cm-2) > September (1.51±0.50 μg·cm-2). The leaves of P. bungeana and P. tabuliformis were rugged with many recesses and protrusions, large relative height difference, and high roughness, and their absorption ability of PM2.5 was strong. The leaves of S. babylonica and A. mono had folded leaf lamina and were covered by fine hairs, and their roughness was relatively high, with many protrusions and fillisters on the leaf surface. Since G. biloba and P. davidiana had smooth leaves, mostly oblong stomata and low roughness, their PM2.5 absorption ability was weaker. The ranking of average roughness on the ada-xial and abaxial side of the leaves was as follows: P. bungeana (149.91±16.38 nm) > P. tabuliformis (124.47±10.52 nm) > S. babylonica (98.85±5.36 nm) > A. mono (93.74±21.75 nm) > G. biloba (80.84±0.88 nm) > P. davidiana (67.72±8.66 nm). This accorded with PM2.5 adsorption per unit leaf area, and leaf roughness had a significant positive correlation with PM2.5 adsorption amount per unit leaf area as well (R2=0.9498). To improve the environmental effects of city vegetation, tree species with leaf surface morphology that facilitates absorption of PM2.5 and other particles should be selected.