An Observation Study On Summertime About Properties Of Aerosol Hygroscopic Growth And Activation And PM_2.5 Chemical Compositions In Urban Area Of Nanjing

The properties of aerosols’ hygroscopic growth and activation can have significant effects on particle number size distribution, optical properties, cloud formation, climate forcing and human health. In this study, a Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA) was utilized to observe the hygroscopic parameters at 90% relative humidity (RH) for sub-micron particles. A Cloud Condensation Nuclei Counter (CCNC) was employed to measure the number concentration of CCN (NCCN) at supersaturation of 0.2%-0.8%. Simultaneously, a medium-sized sampler was used to collect PM2.5 samples for further analysis. Observation started from August 2 to 30 and the main conclusions are as follows:(1) The hygroscopic growth behavior of size-resolved aerosols at high relative humidity was researched in Nanjing. It was found that aerosols of Aitken nuclei and accumulation nuclei contained different soluble constituents, in particular expressed distinct differences in hygroscopic growth factor. In addition, because the source and forming process of the small and large particles were not the same, which resulted in large particles was closer to internally mixed state compared to small particles and its chemical composition also tended to more stable. According to research and analysis of CCN in different supersaturation, there were many particles diameter less than 100nm in this area, and always included soluble organic matter or formation by gas phase to secondary organic aerosols (SOA). Therefore, these particles had a better hygroscopicity and were easy to activate to CCN. Aerosols at Mt. Huang in more-hygroscopic model had a stronger hygroscopicity than those in Nanjing, and therefore were easier to activate to CCN.(2) By using the k-Kphler equation to connect aerosol hygroscopic growth to activation process, size-resolved aerosol hygroscopic growth factor from H-TDMA can calculate critical activation diameter (D50) in different supersaturation. Then CCN number concentration could be calculated from aerosol number concentration over D50. A comparison of the NCCNn calculated from hygroscopic parameter-k with actual measured NCCN proved to be a good correlation, indicating that the hygroscopic parameter-k under sub-saturation from hygroscopic measurement may well predict the activation ability of aerosols to CCN under supersaturation.(3) The analysis of the PM2.5 particles and its composition expressed that inorganic ions, organic matters and elemental carbon occupied the largest proportion and accounted for about 66.68% of the total PM2.5. Secondary inorganic aerosols (NH4+、SO42- and NO3-) had a larger possession of the total inorganic ions. By analyzing the relationship between organic carbon and elemental carbon, it was concluded that they were from different sources and SOA, as a part of OC, will influence the aerosol hygroscopicity. Source apportionment of PM2.5 was conducted with positive matrix factorization(PMF) method and traffic emissions, secondary aerosols, residential cooking, road dust and crust elements was considered to be the major contribution source to the composition of PM2.5.Meanwhile, we can explain how emission source and relative composition could influence the aerosol hygroscopic growth behavior and activation process.