Characteristics And Sources Of Atmospheric Polycyclic Aromatic Hydrocarbons (PAHs) At An Urban Site Of Guiyang City

Polycyclic aromatic hydrocarbons?PAHs?are volatile hydrocarbons produced during incomplete combustion of coal,petroleum,wood and organic polymer compounds.PAHs are a kind of important environmental organic pollutants with carcinogenic,teratogenic and mutagenic effects.Because of their strong health hazards,they have attracted extensive attention.Atmospheric PAHs exist in the form of particle phase and gas phase.Under certain conditions,particule phase PAHs and gas phase PAHs can transform into each other,Simultaneous research on pollution characteristics of atmospheric particle phase PAHs and gas phase PAHs is of great significance for a comprehensive understanding of atmospheric PAHs migration and transformation and source analysis.In the present study,atmospheric PAHs collected at an urban site of Guiyang City were investiaged.Concentrations,temperal varations,and potential sources of both particle phase and gas phase were elucidated.The results will provide a data base and an evidence for local departments to implement the controlling of atmospheric PAHs emission in future.The top roof of a seven-storey building in Guizhou Normal University,Yunyan District of Guiyang City was selected to simultaneously collect particle phase PAHs(PM_2.5)and gas phase PAHs from September 2017 to August2018 using the versatile air pollutant sampler URG-3000K?USA,URG Corp.?.A total of 270 mixed atmospheric PAHs samples were collected within 12months.Samples of particle phase PAHs and gas phase PAHs were extracted by accelerated solvent extraction?ASE?and Soxhlet extractor,respectively,then purified by chromatography column,and finally analyzed by ultra high performance liquid chromatography?UPLC?.Total of 270�16 PAHs data were obtained in the present study.Based on the data-set,the concentration and temperal variation of atmospheric PAHs were elucidated.The influencing factors and potential sources of PAHs were discussed as well.The results are as follows:The total concentration of PAHs in Guiyang is 69�32 ng�m^-3,which is lower than that in other cities in the world.The concentration of gas phase PAHs is slightly higher than that of particle phase PAHs,with concentration of 39�18 ng�m^-3 and 30�26 ng�m^-3,accounting for 56%and44%of the total,respectively.The daily average concentrations of particle phase PAHs range between 0.69 and 79 ng�m^-3,and that of gas phase PAHs between 6.1 and 59 ng�m^-3.The monthly average maximum and minimum values of particle phase PAHs occur in April and August,respectively,while for gas phase PAHs in December and October,respectively.Seasonal trends of particle phase PAHs and gas phase PAHs are as follows:winter and spring>summer and autumn.The concentrations of particle phase PAHs and gas phase PAHs are slightly higher during daytime than that observed during nighttime,probably thanks to more frequences of residential activities at daytime than nighttime.For 16-species PAHs,the larger the molecular weight of PAH,the easier it is to adsorb on the particle phase.Particle phase PAHs and gas phase PAHs exhibit similar trends of ring number distribution,showing 2-3 rings>4 rings>5-6 rings.The proportions of 2-3 rings,4 rings,and 5-6 rings in particle phase PAHs are 51%,27%,and 22%,respectively,and corresponding for gas phase PAHs are 66%,24%and 10%,respectively.Compared to particle phase PAHs,the proportion of 2-3 rings PAHs in gas phase PAHs was higher.There was a strong positive correlation between particulate PAHs and PM_2.5 concentration?r=0.51,P<0.001?,and 5-6 rings?r=0.55,P<0.001?were stronger than 4 rings?r=0.50,P<0.001?and 2-3 rings?r=0.40,P<0.001?,indicating that high molecular weight PAHs were easier bound to PM_2.5.Particle phase PAHs have a negative correlation with temperature?r=-0.50,P<0.01?and a positive correlation with pressure?r=0.16?,which may be due to the photochemical reaction of particle phase PAHs promoted by high temperature and low pressure,and generates other regenerated pollutants and reduces the concentration of particle phase PAHs,or the conversion of particle phase PAHs to gas phase PAHs may be facilitated by high temperature and low pressure conditions.Different from particulate PAHs,the correlation between low-ring PAHs in gas phase PAHs and meteorological parameters is more significant.Gaseous PAHs have a negative correlation with temperature?r=-0.38,P<0.01?and a positive correlation with pressure?r=0.24,P<0.01?,which may be due to high temperature,thick atmospheric boundary layer and easy upward diffusion of pollutants,resulting in a decrease in the concentration of collected gas phase PAHs.It is negatively correlated with wind speed?r=-0.28,P<0.01?,on the one hand,the higher the wind speed,the more favorable the dilution and diffusion of pollutants,resulting in a decrease in the concentration of gas phase PAHs.on the other hand,the wind speed may be conducive to the migration of gas phase PAHs to particle phase PAHs or media such as soil and water.Diagnosistic ratios'results showed that the main sources of particle phase PAHs and gas phase PAHs were volatilization of petroleum and combustion of coal,biomass and liquid fossil fuels.Principal component analysis?PCA?showed that the sources of particle phase PAHs were combustion of coal and biomass,motor vehicle exhaust emissions,coke oven volatilization and other unknown sources,with contribution rates of 59%,11%,6%and 24%,respectively.The sources of gas phase PAHs were combustion coal and biomass,vehicle exhaust emission,oil combustion,coke oven volatilization and other unknown sources,with contribution rates of 29%,21%,9%,7%and 34%,respectively.PMF model results show that the sources of particle phase PAHs were coal combustion,biomass combustion,coke oven volatilization and vehicle exhaust emission,with contribution rates of 49%,18%,24%and 9%,respectively.The sources of gas phase PAHs were coal combustion and coke oven volatilization,oil combustion,biomass combustion and vehicle exhaust emissions,with contribution rates of 56%,19%,16%and 9%,respectively.The back trajectory model?HYSPLIT?shows that the transmission of air pollutants mainly comes from the local of Guizhou Province,with certain contributions of surrounding provinces such as Hunan,Chongqing,Yunnan and Guangxi.Seasonal results indicated that approximately 100%of pollution air masses in spring,autumn and winter come from Guizhou Province and surrounding regions of China,however,approximately 28%of pollution air masses in summer come from Vietnam with a long-distance transmission.The proportion of polluted air masses from the local of Guizhou Province reached the highest,with contribution of 43%in autumn,61%in winter,38%in spring,and 50%in summer.The polluted air masses in autumn and spring comes from Guizhou,Hunan,Yunnan,Guangxi,and Chongqing,and from Guizhou,Hunan,Chongqing and Yunnan in winter,from Guangzhou and Vietnam in summer.