Seasonal And Spatial Variations And Potential Sources Of Carbonaceous Aerosols In The Yangtze River Delta

Aerosol samples were collected by an Andersen cascade impactor(Andersen)in Nanjing,and organic carbon(OC)and elemental carbon(EC)in particles were determined by DRI Model 2001A carbon analyzer of USA.Based on the observations,the seasonal and particle size distribution characteristics of OC and its components(OC1?4,OP),EC and its components(Char-EC and Soot-EC)were analyzed,and a variety of methods were used to identify the sources of carbonaceous aerosol.Meanwhile,there was a continuous regional heavy air pollution episode in winter in the Yangtze River Delta(YRD)during Jan 13rd to 28rd in 2015,to characterize the regional distribution and identify the sources of carbonaceous aerosol and different carbon components in pollution days,continuous measurements of PM2.5 were conducted in three cities-Nanjing,Suzhou,Lin' An.Results showed that,OC and EC in PM10 showed similar seasonal fluctuation,which were higher in winter and autumn while lower in summer and spring.OP accounts for a relatively small proportion in OC,and the proportion of OP accounts for more than 90%of total OP in fine particles.Compared to Char-EC,Soot-EC in fine particles has a higher enrichment in the ultra-fine particle size of less than 0.43 ?m,and the seasonal distribution is more uniform,while the Soot-EC concentration in coarse particles has a larger seasonal variation.OC,EC and Char-EC showed bimodal size distribution,while OP and Soot-EC presented a unimodal size distribution,and the size variations have the same trends in four seasons.Total GMDs in the whole range of impactor sizes were very close to those in the fine mode ones,which indicated that OC and EC in this area were mainly originated from combustion processes.SOC was concentrated in the fine particles,and the concentration in autumn and winter was higher than that in spring and summer.During summer,OC have a good correlation with EC,and Char-EC have a good correlation with EC,indicating the source of carbonaceous aerosol in summer is relatively simple.During spring,autumn and winter,the correlations were poor,indicating the source of carbonaceous aerosol were more complicated during the three seasons.The correlations between OC and EC,Char-EC and Soot-EC were different in different particle size segments.They had a good correation in ultra-fine and coarse particle size segments while had a poor correlation in fine particle size segments.This study made use of carbon profiles and ratios between carbon fractions anc other components of particle matters to identify the pollution sources of carbon fractions.Results showed that coal burning,vehicle emission,biomass burning were the main sources of carbonaceous aerosols in Nanjing;the contribution of diesel vehicle was little.The contribution of motor vehicle exhaust and biomass combustion in the fine-grained section was even more significant,and the contribution of diesel exhaust gas in the ultra-fine-grained section was even more significant.Using the pollution source model analysis method to analyze the contribution of external transport to carbon-containing aerosols,the results showed that the northwesterly airstream has the greatest impact on the carbon-containing aerosols in Nanjing,Henan,Hubei,Anhui,Zhejiang,Beijing-Tianjin-Hebei and the western part of Shandong were the major potential sources of carbonaceous aerosol in Nanjing.The long-distance transport of pollutants in the north is the main factor causing the high concentration of Soot-EC in the coarse-grained section.The Yangtze River Delta(YRD)suffered serious air pollution during the winter season.The carbonaceous aerosol were the important part of PM2.5.The characteristics of different carbonaceous components varied during the pollution episode;the mass concentrations of the primary and secondary organic carbon(POC,SOC)and Char-EC increased from clean days to the heavy pollution days.However,the diurnal variation of Soot-EC was small,and showing relatively well-distributed regional distribution characteristics,which was different from Char-EC.During the pollution episode,the main sources of carbonaceous aerosols were coal burning,vehicle emission,biomass burning also contributed to OC,and EC burden,the contribution of diesel vehicle was little.During the clean days,the air trajectories come from the sea,the air was clean,the sources of carbonaceous aerosols were simple;during the heavy pollution days,the air trajectories come from the northwest and the provinces surrounding the YDR,the sources of carbonaceous aerosols became complicated on account of the pollution from local sources mixing with the pollution from regional transporting.