Number Size Distribution And Source Apportionment Of Atmospheric Aerosols In Northern Suburb Of Nanjing

The behaviors and effects of aerosols in the atmosphere largely depend on their properties---particle size and distribution.The work in this thesis was carried out at the Air Monitoring Supersite in Nanjing University of Information Science&Technology.Particle size distribution data were obtained using the Scanning Mobility Particle Sizer(SMPS)from intensive field campaigns in four seasons,with measured particle size ranging from 10nm-500nm in order to reflect the characteristics of size distribution of ultra-fine particles in the northern suburb of Nanjing.The analysis of Nucleation Mode,Aitken Mode and Accumulation Mode aerosols in four seasons was carried out using statistical methods,mainly focusing on the impacts traffic emissions on different modes.It was found that the Nucleation Mode and Aitken Mode aerosols during four seasons usually peaked in the morning and evening respectively,while the Accumulation Mode was largely affected by atmospheric boundary layer.The three aerosol modes are not well-correlated with trace gas concentrations,especially the Accumulation Mode,suggesting that the Accumulation Mode aerosols were not significantly affected by traffic emissions.Nevertheless,during every morning and evening,the Nucleation Mode and Aitken Mode aerosols showed similar trends with NOx and SO2,indicating that nearby traffic emissions have direct impacts on these modes.Wind speed among meteorological conditions has a significant impact on the number concentration of three modes,with the Nucleation Mode aerosols first increased and then decreased with increasing wind speed,whereas the Aitken Mode and Accumulation Mode aerosols decreased with increasing wind speed.Source apportionment of aerosols was performed based on the size distribution data through Positive Matrix Factorization(PMF)analysis.Combined with the data of trace gases(NOx),aerosol absorption coefficient(Babs781)and chemical composition(SO42-,NO3-),four sources were identified,i.e.adjacent traffic emission source,long-distance traffic emission source,mixed combustion emission source,and secondary aerosol source for summer,winter and spring;and adjacent traffic emission source,long-distance traffic emission source,biomass burning source and secondary aerosol source for autumn.The source apportionment results at Nanjing urban site(Nanjing Meteorology Bureau at Jiangxinzhou)also showed four sources including adjacent traffic emission source,long-distance traffic emission source,mixed combustion emission source,and secondary aerosol source,with slightly higher contributions of mixed combustion source and lower contribution of adjacent traffic emission source compared with the results obtained at the northern suburb.