Characteristics,Sources And Influencing Factors Of PM_2.5-bound Polycyclic Aromatic Hydrocarbons In Different Green Spaces In Lin’an

The relationship between the urban green space and public health has always been a hot topic of discussion.The accelerating urbanization process inevitably leads to an increase in the concentration of polycyclic aromatic hydrocarbons（PAHs）.As an important part of urban ecosystem,urban green space can effectively improve the quality of atmospheric environment and create a healthy living environment.In recent years,with the continuous development of science and technology,there have been many studies on the pollution of PAHs in atmospheric particulate matter in Hangzhou,but few studies have explored the pollution of PM_2.5-bound PAHs within small-scale urban green spaces.In this study,four representative green spaces,namely,"Spring" district,"Yijin" commercial street,"Wuzhou" plaza and the green space next to No.4 College Building in East Lake Campus of Zhejiang Agriculture and Forestry University（college building adjacent green space）in Lin’an district of Hangzhou,were used to sample PM_2.5 within the green space with an intelligent medium-flow TSP sampler and measure PAHs with a gas-mass spectrometer in spring and winter of 2017,respectively,and PAHs pollution characteristics were analyzed using statistical methods,diagnostic ratio method and principal component-multiple linear regression method were used to qualitatively and quantitatively trace the pollution sources,to assess the health risk of human exposure to PAHs based on the toxic equivalents of benzo[a]pyrene.Finally,we explored the main factors affecting PAHs concentrations in green sapces.The main conclusions are as follows.（1）In 2017,PM_2.5 pollution in Lin’an was higher in winter than that in spring（P<0.05）.The variation of single PAH content from high to low is Flu>Chr>BbF>Pyr>BkF>BaA>IcdP>BghiP>BaP.The pollution level of BaP is within the tolerable range of human body.The temporal and spatial variation concentration of PM_2.5-bound PAHs in each urban green space was obvious（P<0.05）,the spatial variation showed that "Yijin" commercial street>"Spring" district>"Wuzhou"plaza>college building adjacent green space,variation of time indicated higher in winter than in spring.The distribution weight of PAHs rings within each green space was 4 rings>5 rings>6 rings from the largest to the smallest in different seasons.The distribution proportion of 4-rings PAH in different urban green spaces was highest in the college building adjacent green space and lowest in the "Spring" district.（2）There were more types of PAHs pollution sources in the four types of green spaces,mainly coal combustion,vehicle exhaust emission,biomass and grass burning."Spring" district,college building adjacent green space and "Yijin" commercial street were mainly mixed sources.In addition to the mixed sources,the contribution of coal and natural gas is high in "Yijin" commercial street,and the main sources were motor vehicle exhaust emissions in "Wuzhou" plaza.In winter,the similarity and correlation of PAHs pollution sources in the four types of green spaces were good and more obvious than in spring.The health risk differed from one green space to another,and all were within the safe range.In comparison,the "Spring" district had higher risk in spring,and "Yijin" commercial street had the higher risk in winter.The health risk of college building adjacent green space was lower than other green spaces in both seasons in spring and in winter.（3）In spring and winter,the concentration of PM_2.5-bound PAHs in the four types of green spaces was influenced by the building layout,greening coverage and pedestrian and vehicular traffic;the concentration of PAHs increased with the increase of pedestrian and vehicular traffic;The negative correlation between greenery coverage and PAHs concentration was significant（P<0.05）or highly significant（P<0.01）.The higher green coverage and lower building density of the college building adjacent green space could effectively retain and accelerate the dispersion of PAHs."Yijin"commercial street with high traffic flow,semi-encircled layout of buildings and low greening coverage could easily lead to PAHs pollution not easily diffused.The high-density building layout in"Spring" district had a greater impact on the concentration of PAHs.The internal space of "Wuzhou"plaza was the most open,and PAHs were less likely to gather and dissipate faster.