Absorption features of PAHs in leaves of common tree species at different PM2.5 polluted places

Leaves of six tree species were collected from two sites with different atmospheric PM2.5 levels in Beijing, i.e., the National Olympic Forest Park and Xizhimen traffic hub. The components and concentrations of PAHs absorbed were measured using high performance liquid chromatography, and were compared among the six tree species. The relationship between leaf PAHs concentration and atmospheric PM2.5 level was preliminarily investigated. The results showed that PAHs contents in the leaves of coniferous trees such as Sabina chinensis and Pinus tabuliformis were higher than those of broadleaf trees. The content of PAHs in Amygdalus persica was the highest, followed by Populus tomentosa. In addition, as the pollution was aggravating, tree species could enhance the ability to absorb PAHs to adapt to the environmental pollution. For all the six tree species, PAHs contents in leaves sampled from the Xizhimen traffic hub with higher PM2.5 level were higher than those from the National Olympic Forest Park. Three-ring compounds were the major component in leaf-absorbed PAHs, followed by two-ring, four-ring and five- or six-ring compounds. The contents of compounds with different ring numbers in the leaf samples from Xizhimen traffic hub were higher than those from National Olympic Forest Park. Both three-ring compounds and contents in the leaf samples from Xizhimen traffic hub were higher than those from National Olympic Forest Park. A principal component analysis based on the contents of different PAHs components suggested that the ability of the species to absorb PAHs followed the order of Sabina chinensisAmygdalus persicaPinus tabuliformisPopulus tomentosaUlmus pumilaPrunus cerasifera.