Response of the particulate matter capture ability to leaf age and pollution intensity

Differences in leaf surface microstructure characteristics can lead to differences in the ability of trees to capture suspended particulate matter (PM). The influence of changes in leaf surface microstructure caused by growth and environmental pollution on the PM capture ability is poorly understood. This study assessed the influence of growth on leaf microstructure in leaves of different ages, and the influence of pollution intensity was assessed by studying trees growing under different pollution conditions. It was found that the ability of leaves of Taxus cuspidata var., Platycladus orientalis, and Pinus tabuliformis to absorb total suspended particles (TSP), PM₁₀, PM_2.5, and PM₁ increased with leaf age. The amounts of TSP and PM₁₀ captured by P. orientalis, P. tabuliformis, Sophora japonica, Populus tomentosa, and Ginkgo biloba were higher in heavily polluted areas than in clean areas. This may be because particle capture is influenced by leaf microstructure changes. With age increasing, the root mean square roughness (R_q) of three evergreen species leaves increased. Environmental pollution will change the leaf surface microstructure and its ability to capture PM. Compared with a clean area, in a heavily polluted area, the stomatal index of the leaves decreased, stomata were occluded, the leaf wax layer was degraded, the leaf surface contained more particles, the surface texture of S. japonica and G. biloba leaves became irregular, the boundaries of the epidermal cells became more irregular, and the trichrome of S. japonica became thinner, longer, and harder. The R_q value was generally higher in the heavily polluted area, and the roughness of the abaxial surface increased more than on the adaxial surface. In the heavily polluted area, the leaf microstructure changes were the main reason for the increase in the R_q value. With the increase in leaf roughness, the amount of PM on the leaf surface increased.