Characteristics Of Carbonaceous Aerosols Over The East China Sea From 2011 To 2015 And Source Contribution Of PCBs Indicated By OC/EC

In this study,387 particulate samples（from autumn 2011 to winter 2015）and 94gaseous samples（from autumn 2013 to summer 2014）were collected from Huaniao Island.The organic carbon（OC）and elemental carbon（EC）components were determined by Thermo-Optical Carbon Analyzer.The concentrations of total suspended particulate matter（TSP）,char-EC,soot-EC and secondary organic carbon（SOC）in particulate samples were calculated,and 34 kinds of polychlorinated biphenyls（PCBs）in particulate and gaseous samples were detected by GC.The time variation characteristics,source composition and pollution event characteristics of each carbon-containing component were analyzed.Based on positive matrix decomposition（PMF）,the OC and EC data from 2013 to 2014 were used to identify the combustion sources of PCBs in the same year.The main conclusions are as follows:（1）The average annual TSP concentration in the East China Sea varies from 47.58to 105.13μg·m^-3,lower than the national standard average annual concentration limit(200μg·m^-3)for the second-class functional areas,indicating that the air quality in the East China Sea is relatively clean,but the atmospheric particulate pollution trend is worsening.In spring,the atmospheric particulate pollution was mainly caused by dust aerosols in north and northwest China.The annual occurrence of dust in China was positively correlated with the change of TSP concentration.In summer,pollution sources are relatively less and favorable meteorological conditions promote a cleaner atmosphere.In autumn,the air pollution in the East China Sea mainly comes from the burning of crops after the autumn harvest in the nearby Yangtze River Delta.In this study,the sampling time in winter coincides with the heating time in northern China,showing obvious high particle pollution.OC and EC accounted for 3.41%±2.04%～17.62%±44.61%and 1.07%±0.75%～5.60%±9.10%of TSP,respectively,indicating that the carbon aerosol pollution in atmospheric particulate matter was mainly OC pollution.There was a strong correlation between the two（Pearsons coefficient 0.87）,which proved that they had the same pollution source.The average concentrations of OC and EC in winter were 2.31-3.92times and 1.57-3.55 times higher than those in summer,respectively,indicating that the carbon aerosol pollution in the East China Sea was more serious in the cold season.The average daily concentration of char-EC and soot during the sampling period ranged from undetected to 7.38μg·m^-3 and undetected to 2.25μg·m^-3,which was compared with the stable concentration of soot-EC between different seasons.char-EC has a significant seasonal trend,and the average concentration of char-EC in winter is 3.77-4.54 times higher than that in summer.（2）Correlation analysis found that OC1～OC4 was highly correlated;OC showed strong correlation with other components except soot-EC,EC2 and EC3.The correlation between TSP and other components is very weak.soot-EC and char-EC show different correlation,which is related to their formation pattern and characteristics.The seasonal correlation between OC and EC indicates that the pollution sources of OC and EC are similar in cold season,mainly primary pollution sources（fossil fuel combustion and automobile exhaust emissions）,while SOC generation affects the pollution source structure of OC in warm season.The correlation between char-EC and soot-EC showed no seasonal or temporal variation.The ratio of OC/EC during the sampling period ranged from 0.69 to 28.11,with an average of 3.68±2.33.The char/soot ratio ranged from 0.01 to 76.00,and the mean value was 4.63±6.79.In the seven OC and EC components,the sum of OC2,OC3,OC4and EC1 is 83.57%～92.16%,indicating that the sources of atmospheric carbon aerosol pollution over the East China Sea mainly include automobile exhaust emissions,fossil fuels such as coal,biomass combustion,road dust,etc.By comparing FIRMS system statistics of monthly ignition points and OC/EC,char/soot ratio,we guess that the serious pollution of carbon aerosol in autumn 2014 was mainly caused by biomass emissions from straw burning in open air,and it is mainly the secondary pollution source.SOC pollution in the East China Sea is most serious in winter,but the generation rate is higher in the warm season.（3）During the sampling period,TSP,OC,EC,char-EC,soot-EC and SOC pollution occurred 6,10,5,9,8 and 16 times respectively,and the change of pollution source structure was one of the main causes of pollution events.Because of the lack of direct emission sources of carbon aerosols,secondary aerosol pollution events occurred frequently.The second is OC pollution with low temperature combustion generation and long-distance transmission characteristics.We guess that the air in the East China Sea is mainly threatened by autumn.Compared with the long-distance pollution caused by heating in the north,close-range biomass sources and automobile exhaust are more likely to have adverse effects on the air quality in the East China Sea.（4）Combustion and non-combustion sources of PCBs were determined by OC/EC data from Autumn 2013 to summer 2014,and four factors were obtained by source analysis according to PMF.We conclude that factor 1 is mainly derived from PCBs generated by combustion and decomposition of e-waste,factor 2 is the low-temperature combustion source of PCBs,factor 3 is mainly brought by cold and dry dust carrying PCBs for long-distance transportation,and factor 4 is mainly derived from the re-discharge or weathering source of historical use of PCBs.In this study,factor 1 and factor 2 were used as combustion sources of PCBs,and factor 3 and factor 4 were used as non-combustion sources,accounting for 30%and 70%ofΣPCBs respectively.