The Rhythmicvariation Of Concentration Of PAHs In The Leaves Of Urban Afforestation Species

Polycyclic Aromatic Hydrocarbons (PAHs) are a kind of trace toxic organic pollutants which widely exist in global environment. They are one of the environmental pollutants which earliest known for their cancerogenic, teratogenetic and mutagenic. With the progress of modern city and the rapid increase of vehicles, the safety of city have been threatend by PAHs in urban air which are caused by automobile emissions.In this experiment, five urban afforestation species including Cinnamomum camphora, Osmanthus fragrans, Magnolia grandiflora, Redrlowered Loropetalum and Pinus massoniana in the campus of Central South Univesity of Foresty and Technology and Tianjiling National Forestry Park were chosen.The concentration of PAHs in leaves has been tested for one year, the rhythmivariaition such as diurnal variation, monthly variation and seasonal variation has been discussed, so as to compare the absorption ability of PAHs of different greening tree species, provide theoretic evidence for selecting of better trees which have great effect on removal of PAHs in urban air.The average concentration ofΣPAHs of the four urban afforestation species in the campus sample plot ranged from 3.2408 to 5.2813 mg/kg, and the concentration were in the following order:Redrlowered Loropetalum> Cinnamomum camphora> Osmanthus fragrans> Magnolia grandiflora.The average concentration ofΣPAHs of the 5 urban afforestation species in Tianjiling sample plot were range between 3.2408 and 5.2813 mg/kg, and the concentration were in the following order:Pinus massoniana> Cinnamomum camphora> Osmanthus fragrans> Redrlowered Loropetalum>Magnolia grandiflora.In the two sample plot,2～4 ring PAHs were the main components of the 16 PAHs, and accounted for more than 90%, the 5～6 ring PAHs taken a small percentage ofΣPAHs, only about 10%. Compared with other individual PAHs, PHE taken the higest percentage of E PAHs in all species.The concentration of PAHs in the upper leaves of Cinnamomum camphora and Osmanthus fragrans were higher than other two levels in campus sample plot, but there were no significant differences among the there levels. The concentration of PAHs in the lower leaves of Cinnamomum camphora, Osmanthus fragrans and Pinus massoniana were higher than other two levels in Tianjiling sample plot, and there were no significant differences among the there levels.The concentrations of the total PAHs in the leaves of four urban afforestation species in the campus sample plot in the daytime were much lower than those at night in October and July, and it take on a single peak curve over time. Conversely, the of concentration of PAHs in the leaves of four urban afforestation species in the daytime were higher than those at night in January and April.The concentration of PAHs in the leaves of five urban afforestation species were higher in autumn and winter, while the PAHs had a low content in spring and summer in both sample plot. The peak value occured in autumn. The concentration of PAHs decrease with time, descend from September,2008 to May,2009, and then, ascend from May to July.The PAHs in leaves had a complex sources. The ratios of indicator PAHs method was applied and indicated that the PAHs in the leaves of the five urban afforestation species had originated from both petroleum and pyrolytic.