| Atmospheric particulate matter(PM),mainly including water-soluble ions(WSI),carbon components and inorganic metal elements,has become the primary pollutant in most cities.The size distribution characteristic of chemical component mass concentration is one of the most important properties of atmospheric PM,related to its sources and formation processes as well as environmental and health effects.Totally 207 samples of size-fragmented PM were collected using an 8-stage Anderson cascade impactor in the four seasons in 2016 at the Xianlin campus,Nanjing University.Size distribution characteristics of the PM and chemical components mass concentrations,and possible sources of the size-fragmented PM were studied,which are meaningful for further researches on health effects and for policy making for air pollution control.The main results are as follows:(1)Yearly averaged size distribution of the PM mass concentration is bimodal,peaking at 0.4-1.1 and 5.8-9μm,respectively.Size distributions of the PM mass concentrations in the four seasons shows bimodal,peaking at 0.7-1.1 and 5.8-9μm,respectively.The two peaks are close in winter and spring,with the highest peak value in winter and the second higher peak value in spring among all seasons.In summer and autumn,the peak at fine size segment is much higher than that at coarse size segment.Summer has the lowest peak value and the peak at fine size segment shifts towards the smaller diameter segment,while there is a significantly increase in the PM mass concentration within the size of 0.4-0.7μm in the autumn.(2)With regard to size distribution of metal elements,we found three types.The first type has a mono peak at coarse size segment(3.3-5.8μm),including Na,Al,Ca,Mg,Co,Ce,Sr and Ba.The second has a mono peak at fine size segment(0.4-1.1μm),including Zn,As,Cd,Ag,T1 and Pb,and the third has two peaks at fine(1μm)and coarse(5μm),respectively,including K,Se,Li,Be,Mn,V,Cu,Cr,Ni and Fe.According to the Enrichment factors(EFs),the elements were divided into three groups.They are a slightly enriched group with EFs lower than 5(Ba,Ca,Ce,Sr,Mg,Fe,Co,Mn,Be and V),a moderately enriched group with EFs between 5 and 100(Li,Na,Ni,K and Cr),and a highly enriched group with EFs larger than 100(Cu,T1,Zn,As,Pb,Ag,Cd and Se).The results of the principal component analysis(PCA)showed that soil dust,chemical industry combustion,vehicle exhaust emission,coal burning and road traffic non-emission were the main sources of coarse PM.Metallurgical chemical emission,road traffic source,biomass burning,fuel combustion,and steel industry emission were the main sources of Fine PM.(3)The size distribution of organic carbon(OC)is bimodal,peaking at 0.7-2.1 and 3.3-5.8μm.The size distribution of elemental carbon(EC)is bimodal,peaking at 3.3-5.8 and 0.4-1.1μm.The correlation analysis showed that there was good relationship between OC and EC in the PM within the range of<0.4 and 1.1-4.7μm suggesting that they may have the same sources.The correlation between OC and EC in the PM within the range of>4.7μm is poor,suggesting their sources are different.The OC/EC ratios of the PM2.1 in winter,spring,summer and autumn are 3.7,2.1,3.6 and 4.4 respectively,suggesting that carbon components in fine PM is mainly emitted by fuel combustion and traffic source while carbon components in coarse PM was mainly emitted by soil dust,fuel combustion and traffic source.The size distribution of the secondary organic carbon(SOC)is bimodal,peaking at 0.4-2.1 and 3.3-9μm.It suggests that the SOC pollution of fine PM is serious in Nanjing and there is large seasonal variation in the size distributions of SOC mass concentrations.The analysis of all carbon components indicated that coarse PM was mainly emitted by gasoline exhaust and coal combustion,and fine PM was mainly emitted by road dust,motor vehicle exhaust and coal combustion.(4)Size distributions of WSIs vary considerably.SO42-,NH4+and K+have a mono peak at 0.7-2.1,0.4-2.1 and 0.7-2.1μm respectively.F-and Na+ shows bimodal,with the main peak at 2.1-9 and 2.1-5.8μm respectively,and the secondary peak both at 0.4-1.1 μm.Ca2+and Mg2+ have a mono peak at>9 and 2.1-9μm respectively.The size distribution of NO3-is bimodal in spring and unimodal in the other seasons.Cl-is distributed evenly among all segments in spring and autumn and it has a mono peak in winter and summer.Correlation analysis showed that NO3-and SO42-,K+and NH4+,Ca2 and Mg2+might have the same sources.NH4+mainly exists in the form of NH4NO3 and(NH4)2SO4 in the fine PM,and Ca(NO3)2 and CaSO4 are the major components of coarse PM.Yearly averaged ratios of[NO3-]/[SO42-]in fine and coarse PM are 1.34 and 1.02 respectively.It suggests that the contributions of mobile source(mainly motor vehicle pollution)and stationary source(mainly fuel combustion)to fine PM are roughly equal and the influence of mobile source on coarse PM is more significant.Yearly averaged values of sulfur oxidation rate(SOR)and nitrogen oxidation rate(NOR)are 0.33 and 0.19,suggesting that the secondary pollution occurs throughout the year.(5)The results of PCA on chemical compositions showed that coarse PM was mainly emitted by soil dust,industry emissions,metallurgy,vehicle emissions,coal burning and biomass combustion.Fine PM was mainly emitted by coal burning,secondary pollution,soil dust,traffic source and waste incineration. |
PDF Full Text Request