[PM2.5 adsorption capacity of Osmanthus fragrans and Cinnamomum camphora leaf surface and influencing factors under different pollution levels in Changsha, China]

Abstract

To understand the PM_2.5 adsorption mechanisms of plants under different pollution levels and analyze pollutant sources, the PM_2.5 adsorption amount of the leaves of two garden plant species (Cinnamomum camphora and Osmanthus fragrans) in different polluted level area (traffic area, culture and education area, cleaning area) of Changsha was measured using an aerosol generator. AFM scanning was used to obtain leaf surface micromorphological characteristics. Ion chromatography was used to measure the water-soluble ion content. Results showed that amount of PM_2.5 adsorbed by leaves was positively correlated with pollution levels. The annual mean value of PM_2.5adsorbed per leaf area of different plants was traffic area (0.56±0.04 μg·cm^-2) > culture and education are (0.48±0.06 μg·cm^-2) > clearing area (0.33±0.02 μg·cm^-2). The season with amount of PM_2.5adsorbed in leaves from the highest to lowest was winter (0.70±0.10 μg·cm^-2) > spring (0.43±0.14 μg·cm^-2) > autumn (0.39±0.12 μg·cm^-2) > summer (0.31±0.09 μg·cm^-2). Osmanthus fragrans had higher capacity to absorb PM_2.5 than Cinnamomum camphora. Leaves of plants grown in low pollution areas were relatively smooth, whereas those in high pollution areas were rough. The order of leaf roughness in both species from high to low was traffic area (195.45±16.09 nm) > culture and education area (176.99±8.45 nm) > cleaning area (131.88±12.98 nm). The PM_2.5 ionic content was the highest in winter, intermediated in spring and autumn, and the lowest in summer. The PM_2.5 ions mainly included Na⁺, NH₄⁺, Cl^- and Br^- in three pollution areas. PM_2.5 pollution was due to removable source pollution at different pollution levels.

Keywords: PM 25 adsorption amount; leaf surface morphology; pollution degree; water-soluble ionic characteristics.