urbanization

PAHs

tree species

foliage dust retention

Polycyclic aromatic hydrocarbon (PAHs)

The foliar surface of plants can capture atmospheric pollutants. Foliage dust is especially useful for passive adsorption of anthropogenic polycyclic aromatic hydrocarbons (PAHs) present in total suspended particles (TSPs). The objective of this study was to compare the dust-retaining capability of typical trees along an urbanization gradient in Nanjing, China. We also studied the concentrations of 16 PAHs in the foliage dust of four typical tree species. We concluded that the dust-retaining capability of the four typical tree species generally decreased in the order: Firmiana simplex > Symplocos sumuntia > Photinia serrylata > Osmanthus fragrans. The highest amounts of dust per unit leaf area were captured by F. simplex, and the mean values were 84.57, 63.11, and 56.29 μg·cm^-2 in urban, suburban, and rural areas, respectively. PAH concentrations in foliage dust in urban areas were significantly higher than those in suburban and rural areas. Our results suggested that grooves surrounding the stomata and the distribution of tomentum over the leaf surface were the most important factors affecting the accumulation of dust, by facilitating the capture of fine dust particles, which tend to have higher PAH concentrations than larger particles. Scanning electron microscopy (SEM) of the leaf surface of F. simplex revealed that it was covered by tomentum, with grooves surrounding the stomata, and identified this species as a potential biomonitor for atmospheric pollution. From this study, it is evident that PAH concentration of foliage dust can act as indicator of air pollution.