The Tree Species Selection According To The Absorption Of Atmospheric Polycyclic Aromatic Hydrocarbons In Beijing

The serious air pollution in Beijing has become an important urban ecological problem.And there are some air pollutants in Beijing which we should pay attention to,especially polycyclic aromatic hydrocarbons.This research took some garden trees in Beijing as the research object and studied the leaves’ absorption of atmospheric polycyclic aromatic hydrocarbons.The method of extraction and cleaning was established.And the content of polycyclic aromatic hydrocarbons in 34 kinds of garden trees’ leaves in Beijing were tested by the method mentioned above.The species differences in the content of polycyclic aromatic hydrocarbons between those trees were studied so as the seasonal variation of polycyclic aromatic hydrocarbons in leaves and differences of the content of polycyclic aromatic hydrocarbons in leaves in different plots.The correlations between the characteristics of leaves and the content of polycyclic aromatic hydrocarbons in leaves were studied too.The selection of tree species was made according to the content of polycyclic aromatic hydrocarbons in leaves to figure out the influences of leaves’ characteristics to the content of polycyclic aromatic hydrocarbons in them,which could provide scientific experimental basis for the construction of urban greening trees selection.The main results of this study are:(1)The method of extraction and cleaning was made.The best condition of this method is:take ultrasonic extraction for 20min,repeat 3times,and take 15g alumina as absorbent and 80ml eluent.The recovery of this method is 72.1～92.5%.(2)In the studied 34 kinds of tree species,Pinus bungeana,Pierocarya stenopiera,Fraxinus pennsylvanica,etc.had the highest content of total PAHs in leaves;Cercis chinensis,Picea meyeri,Amygdalus triloba,etc.had the lowest content of total PAHs in leaves.Cedrus deodara,Fraxinus pennsylvanica,Pterocarya stenoptera and Pinus tabulaeformis had the highest content of cancerigenic polycyclia aromatic hydrocarbons in leaves while Sabina chinensis,Cercis chinensis,Syringa oblate and Buxus megistophylla had the lowest content in leaves.(3)9 kinds of evergreen trees were taken as the object of the study about seasonal variation of the content of polycyclic aromatic hydrocarbons in leaves was studied.And the content of polycyclic aromatic hydrocarbons in those leaves reached to the top in winter and bottom in summer.(4)Comparison was made to the leaves in rural and different kinds of plots in urban to learn the order of the same tree species’ leaves in different plots.And the result showed that the same tree species in different places had the same order in the content of total polycyclic aromatic hydrocarbons and different orders in different kinds of kinds of polycyclic aromatic hydrocarbons in leaves.(5)The characteristics of leaves may influence the absorption of polycyclic aromatic hydrocarbons.The leaves which had the high content of polycyclic aromatic hydrocarbons might have the rough surfaces;the length and width of stomata’s’,the lipid content of leaves and the specific surface area were related to the content of total polycyclic aromatic hydrocarbons in leaves.And there were not any correlations between the ratios of stomata’s length and width and the content of total polycyclic aromatic hydrocarbons.Pinus bungeana,Pterocarya stenoptera,Fraxinus pennsylvanica,Eucommia ulmoides and Amygdalus persica var.persica f.duplex were selected as they had high absorption capacity.The trees which had high content of polycyclic aromatic hydrocarbons might not have the high content of cancerigenic polycyclic aromatic hydrocarbons.The absorption of polycyclic aromatic hydrocarbons in leaves was influenced by season,environment in different experiment plot,length and width of stomata,lipid content of leaves and specific area.There were not anu relations between the ratios of stomata’s length and width and the content of polycyclic aromatic hydrocarbons.