Characteristics And Source Apportionment Of Black Carbon In The Yangtze River Delta Of China

China is one of the main source region of black carbon(BC)emissions.Severe BC pollution has an important impact on climate change,air quality and human health.The Yangtze River Delta region is the high BC emission area in China.In this study,five stations were selected for comprehensive observation in the Yangtze River Delta region,and a detailed analysis of Nanjing,the Yangtze River Delta typical city,was carried out.The data of black carbon(BC),combined with meteorological factors and trace gases in Shanghai Dongtan(DT),Shanghai Pudong(PD),Anhui Shouxian(SX),Zhejiang Linan(LA)and Zhejiang Hongjia(HJ)in 2016,have been used to study characteristics and source of BC in the Yangtze River Delta region.Based on the Aethalometer model,the source of BC in Nanjing is studied quantitatively.The results show that:(1)The annual average mass concentration(±standard deviation)of BC in DT,PD,SX,LA and HJ sites were 83±1713ng/m3,2410±1537ng/m3,2823±1759ng/m3,2651±1518ng/m3 and 2544±1399 ng/m3.BC concentration in the winter was higher,and it was close in spring,summer and autumn.The BC concentration is relatively low in DT and other sites are very similar.The mass concentration of BC showed a distinct seasonal variation in five sites.The BC concentration in DT site is higher in winter than in other seasons.The BC mass concentration in other sites ranked in the order of winter>spring>autumn>summer.The diurnal variations of DT site in four seasons were not obvious.However,the diurnal cycles in other sites were similar with the high values in rush hours(6-9 a.m.and p.m.)in all seasons.The vehicle emissions and coal combustion were mainly sources of BC in PD,SX,LA and HJ sites.A low wind speed(<3 m/s)occurred in all sites.Low BC concentration accompanied with the high wind speed.The highest BC mass concentration occurred when RH=50-60%.The potential source contribution function(PSCF)analysis signified that the potential sources of all sites in winter and summer were mainly from Jiangsu,Anhui,Zhejiang Province and so on.(2)The seasonal average BC concentration is 980 ± 810 ng/m3(the average value ± the standard deviation),1062 ± 986 ng/m3,1168 ± 937 ng/m3 and 2117 ± 1549 ng/m3 during spring,summer,autumn and winter,respectively.The source apportionment results reveal that liquid fuel(e.g.,traffic)has higher seasonal contributions(ranging from 70%in autumn to 84%in winter)to total BC concentrations than solid fuels do(e.g.,coal and biomass,ranging from 16%in winter to 30%in autumn).The contributions of liquid fuel revealed a major increase during traffic rush hours in all seasons.Solid fuel has higher contributions to total BC concentrations from 22:00-4:00.Meteorological parameters(wind speed and wind direction)provide supportive evidence from BC sources that BC emissions are mainly from local traffic sources and industry coal combustion in the southeast.Moreover,long-range transport from the southwestern regions(mainly Anhui,Zhejiang,Jiangxi and Hunan)of the sampling site also plays a role in total BC concentrations,especially in autumn and winter.The episodes of high BC concentrations under high wind speed in winter are caused by long-range transport from Hebei and Shandong Provinces.High BC in June is from biomass burning activities in the southeastern region of Nanjing and Zhejiang Province.