Seasonal Pollution Characteristics And Cytotoxicity Of PM_2.5 In A District Of Hangzhou City

Air pollution is an important environmental problems in many domestic and foreign cities,and PM2.5 is the main cause of haze events.PM2.5 has complex chemical compositions,such as water-soluble ions,carbon components,metal elements,and polycyclic aromatic hydrocarbons(PAHs),which has a significant impact on atmospheric visibility,climate change and human health.Therefore,to control of air pollution and prevention of health risks,it is important to study the chemical compositions,potential sources and cytotoxicity of PM2.5.In order to explore the key toxic chemical components of PM2.5 as well as its potential sources,PM2.5 samples were collected from September 2015 to July 2016 in Hangzhou.Based on the analysis of the seasonal characteristics of the chemical components of PM2 5,on one hand,the potential source regions of PM2 5 in different seasons are simulated by the backward trajectory model.On the other hand,the toxicity of water-soluble extracts and organic extracts of PM2.5 on human bronchial epithelial cells(BEAS-2B)were compared,the correlations between cytotoxicity and chemical components were analyzed,and the sources of chemical components affecting cytotoxicity were discussed.The main conclusions are as follows:(1)Variation of PM2.5 and main gaseous pollutants:During the study period,the daily average concentration of SO2 and CO reached the first grade standards of air quality.The main pollutants exceeding the standard were NO2,PM2.5 and PM10,and the annual average concentration of these pollutants was 1.19,1.42 and 1.08 times of the second grade standards,respectively.In terms of seasonal variation,PM and NO2 were severely over-standard in winter,and the high concentration of O3 in summer could not be ignored.PM2.5 had a strong positive correlation with SO2,CO and NO2 in spring and winter,while with O.in summer.(2)Seasonal variation of main chemical components in PM2.5:SO42-,NO3-,NH4+and organic matter(OM)were the main substances in PM2.5.The concentration of SO42-and NO3-were the higher in winter and lower in summer.The results of sulfur oxidation ratio and nitrogen oxidation ratio showed the formation of secondary aerosols in winter and spring.The average concentrations of organic carbon(OC)and elemental carbon(EC)were 14.7 and 2.2 ?g/m3,higher in winter and lower in summer.The OC/EC ratio indicated that the contribution of biomass combustion to PM2.5 could not be ignored in autumn and winter.The contribution of metal elements to PM2 5 was small,and average concentration of metal elements was 525.6 ng/m3,which was higher in summer and lower in autumn and winter.The average concentration of PAHs was 25.0 ng/m3,which was higher in winter and lower in summer.And the middle molecular weight-PAHs accounted for a large proportion(47-51%)of total PAHs.BaP toxicity equivalent concentrations in all seasons exceeded guidelines of WHO.(3)Seasonal variation of PM2.5 potential sources:The air masses of northeast and northwest direction was dominant in autumn,winter and spring,while air masses of south and southwest direction was dominant in summer.The potential source region of PM2.5 were mainly Anhui,Henan,Hebei and Ningxia in autumn(80-140 ?g/m3),Jiangxi and Hunan in winter and spring(100-200 ?g/m3),and Southern Zhejiang and Jiangxi Province in summer(50-70 ?g/m3).(4)Cytotoxicity of PM2.5 and main chemical components related:Extracts of PM2.5 can reduce the viability of BEAS-2B,induce the formation of reactive oxygen species(ROS)and interleukin-6(IL-6),and change the morphological of organelles.The toxicity of PM2 5 in autumn and winter was higher than that in other seasons.Compared with water-soluble extracts of PM2.5,organic extracts had the stronger cytotoxicity,resulting in higher cell mortality and lactate dehydrogenase(LDH),ROS,IL-6 levels.Indeno[1,2,3-cd]pyrene(IPY),dibenz[a,h]anthracene(DBA)and benzo[g,h,i]perylene(BPE)were the key components affecting the cytotoxicity of organic extracts,which were mainly from Eastern Zhejiang Province in autumn and Central China in winter.Secondly,the toxicity of water-soluble extracts was relatively small.SO42-,NO3-,NH4+,Mn,V,Ni were the key components affecting the cytotoxicity of water-soluble extracts,which were mainly from North China in autumn,and Central China in winter.In general,the concentrations of PM2.5 and chemical component were higher in winter in Hangzhou,and the cytotoxicity of organic extracts was higher than that of water-soluble extracts.IPY,DBA and BPE were the key components affecting the cytotoxicity of organic extracts,which were mainly from Central China in winter.In the future,joint prevention and control should be strengthened to improve air quality and reduce health risks in a district of Hangzhou.This study can provide new ideas for the prevention and control of air pollution to some extent.