A Study On Characterization And Mechanisms Of PM_2.5-bound PAHs And Carbonaceous Aerosols During Typical Pollution Period In Shanghai

PAHs and black carbon pollution in natural gas environment have been widely concerned by researchers at home and abroad for a long time.The Yangtze River Delta has a dense population and developed industry.In particular,Shanghai has a rapid economic development,rapid urbanization and industrialization,as well as high PAHs emission density,which has caused many atmospheric environmental problems and great harm to human health.In this study,taking Shanghai as the research area and from the perspective of urban environmental process,we carried out long-term phased atmospheric particulate matter sampling.Combined with traditional active sampling technology and eight-stage sampling instruments,we collected atmospheric particulate matter samples with different particle sizes,and collected relevant meteorological parameters and atmospheric conventional pollutant concentrations at the same time.The occurrence characteristics of 16 USEPA optimized PAHs in PM_2.5 were observed and analyzed,and the atmospheric PM_2.5 source contribution,spatial transmission characteristics and human health effects of PAHs were deeply discussed.The main achievements are as follows:(1)Taking fine particulate matter(PM_2.5)as the representative,this study deeply studied the occurrence characteristics of 16 kinds of PAHs optimized by the US Environmental Protection Agency(USEPA)in atmospheric particulate matter in Shanghai.At the same time,we deeply discussed two typical pollution processes(heavy haze event and Spring Festival firework event)the pollutant concentration in different stages and different weather conditions in Shanghai.The influence of meteorological conditions on it is expounded.In typical haze period,the average concentration of total PAHs in heavy haze period is 10.39 ng/m~3,which is about 1.33 times higher than that in fog period(7.80ng/m~3).The average concentrations of seven carcinogenic PAHs in haze period,fog period and clean period were 5.94 ng/m~3,4.12 ng/m~3 and 6.29 ng/m~3 respectively.In the heavy haze period,the corresponding percentages of PAHs with different ring numbers were 4 rings(31.1%)>3 rings(29.7%)>5 rings(24.0%)>6 rings(13.7%)>2 rings(1.5%).However,in the fog period and clean period,the main components of PAHs were3 rings and 5 rings.During the Spring Festival,the overall average concentration of PAHs in PM_2.5 showed the trend of DS(9.75 ng/m~3)>BS(9.16 ng/m~3)>as(6.32 ng/m~3).During the Spring Festival,the corresponding percentages of PAHs with different ring numbers were 3 rings(35.7%)>6 rings(25.0%)>4 rings(17.9%)>5 rings(16.2%)>2 rings(5.2%).For the study on the correlation between PAHs and meteorological parameters in PM_2.5 shows that when the temperature is low,the pollution concentration of PAHs is relatively high.The Spearman correlation coefficients of PAHs concentration with temperature and relative humidity are-0.664(p<0.01)and-0.561(p<0.01)respectively,which may be due to stable atmospheric conditions and caused by the elimination of atmospheric particulate matter by wet deposition and the accumulation of atmospheric pollutants under low relative humidity.(2)The dynamic change characteristics of PAHs emission sources are analyzed and we further clarify the atmospheric PAHs sources under different typical pollution events.The analytical results of positive definite matrix factor analysis model(PMF)show that in Shanghai,the four main sources of PAHs in PM_2.5 are oil volatilization and leakage sources,traffic emission sources,coal and biomass combustion sources and coking emission sources.From 2016 to 2019,two sources that have a great impact on Shanghai's winter PAHs pollution which are traffic emission sources and coal and biomass combustion sources,accounting for up to 31.6%and 33.7%.In the typical haze period,traffic emission sources account for the largest proportion compared with coking sources,coal and biomass combustion sources and petroleum product combustion and volatilization sources,with contribution rates of 33.2%,32.5%,25.5%and 8.87%respectively.Compared with the haze period,the contribution of traffic emission sources is significantly reduced in the clean period,while the contribution of coal and biomass combustion sources is slightly reduced.During the Spring Festival period,coking emission source is the main source,with a contribution rate of 35.40%.Due to the shutdown of factories during the Spring Festival,the sources of coal and biomass combustion decreased sharply during this period,while the coking emission and combustion source increased from 11.50%to 35.40%,mainly because that the discharge of fireworks and firecrackers will greatly increase the contribution rate of combustion source during the Spring Festival.(3)Through the study of PM_2.5-bound carbonaceous aerosols in winter,we revealed the pollution level and particle size distribution characteristics of black carbon,organic carbon and secondary aerosols in typical pollution events in Shanghai.The occurrence characteristics of carbonaceous aerosols are mainly as follows:in the typical haze period,the average concentration of black carbon presents haze period(8.08?g/m~3)>cleaning period(6.67?g/m~3)>fog period(3.57?g/m~3).In addition to high-intensity and high-density vehicle pollutant emissions,the high OC/EC ratio(>2.5)may be related to the rapid formation of secondary organic aerosols caused by pollutants emitted from thermal power plants near the sampling point.In the study of secondary aerosols in PM_2.5,it is found that the correlation between OC and EC shows the trend characteristics of fog period(r=0.85)>clean period(r=0.72)>haze period(r=0.51),indicating that the generation of SOC in the atmospheric environment increases with the increase of pollution degree.The concentrations of atmospheric SOC in haze period was 8.08±3.81?g/m~3,accounting for 52.2%of OC,which may be caused by lower temperature and photochemical reaction.During the Spring Festival,OC is more likely to be enriched in fine particles with a particle size of 0.43?1.1?m.The concentration of OC in 0.43?1.1?m atmospheric particulate matter is 2.24?g/m~3,which is 2.87(0.78?g/m~3)and1.33(1.69?g/m~3)times compared with the time before and after the Spring Festival,respectively.(4)By analyzing the spatial source of PM_2.5-bound PAHs and carbonaceous aerosols in Shanghai,the backward trajectory cluster analysis,potential source contribution function(PSCF)model and concentration weighted trajectory(CWT)model are used to identify the potential source areas of pollutants.In winter,the air flow trajectory mainly comes from the northwest and west directions,of which the northwest trajectory accounts for 50.34%,while west trajectory accounts for 20.08%,and 27.9%of which is exceeded PM_2.5.The concentration of PM_2.5 seriously exceeds the standard which is up to 101.32?g/m~3,which indicate that the pollution of PAHs and black carbon in not only exists in local sources,but also plays an important role in the increase of pollution degree.In the typical haze period,we found that the three clustering directions of air flow trajectories in heavy haze period are WNW,NW and NNW,respectively.The results showed that the average PAHs and EC concentrations from Jiangsu,western Shandong and Hebei were the highest(12.8 ng/m~3,9.41?g/m~3),the higher EC pollution concentration in heavy haze period may be due to the long-distance transmission of pollutants formed by the combustion of coal,biomass and oil in Hebei,Jiangsu and Shandong.The pollution of PAHs is mostly caused by local sources,especially the emissions from chemical plants and thermal power plants near the sampling point.The high PSCF value of PAHs in haze period is significantly distributed in the areas around the sampling points,including the east of Jiangsu province,Anhui province and the north of Zhejiang province,indicating that the pollution level of polycyclic aromatic hydrocarbons is greatly affected by the migration and transmission of pollutants from the industrial zone of the Yangtze River Delta.During the Spring Festival,Zhejiang,Anhui and Hubei provinces were also identified as the potential sources areas of PAHs and carbonaceous aerosols.(5)Through the comprehensive assessment of PAHs health risk in typical pollution events in Shanghai,the results show that in typical haze period,the equivalent carcinogenic concentration and equivalent mutagenic concentration of PAHs showed the characteristics of haze period>clean period>fog period.In the heavy haze period,the concentration of carcinogenic PAHs monomer also increased significantly,which caused great harm to human health.Lifetime carcinogenic risk(ILCRs)model research shows that in the typical haze period,skin contact has the greatest potential harm to human health,up to 1.09×10^-6.While comparing the different stages of typical haze period,the harm degree of PAHs to human body shows the characteristics of haze period>fog period,and the total ILCR values of children,adolescents and adults all reach the degree of 10^-6,indicating that the carcinogenic risk of polycyclic aromatic hydrocarbons is at the"potential risk level".During the Spring Festival,the ILCR values of adult skin contact,respiratory intake and digestive intake were 4.87×10^-6,1.66×10^-8 and 6.72×10^-8,respectively,which indicates that PAHs pollution caused by fireworks during the Spring Festival is potentially harmful to human health.