A study on hygroscopicity and volatility of ultrafine/nano particles using the NanoTDMA technique
Chemical composition of atmospheric ultrafine/nano particles would provide useful insights into their sources, or formation and growth pathways. However, due to the lack of instruments to determine composition of such small particles in real time, understanding of nanoparticle formation and growth or sources for ultrafine/nano particles in the ambient atmosphere has been limited. In this study, we develop a Nano Tandem Differential Mobility Analyzer (Nano TDMA) technique to determine hygroscopicity and volatility of ultrafine/nano particles by measuring particle size changes under elevated relative humidity (5～90％) and temperature (20～300℃). By measuring hygroscopicity and volatility of ultrafine/nano particles almost at the same time, indirect information on their composition can be inferred. For example, elemental carbon particles are expected to show non-hygroscopic and non-volatile behaviors, while ammonium sulfate which has been believed to be one of major candidates for constituents of nanoparticles formed by gas-to-particle conversion process would show high hygroscopicity and varying volatility with temperature. Since water uptake or evaporation behaviors of nanoparticles are expected to be different from those of large particles, extensive laboratory tests should be performed first. Also, internally mixed nanoparticles will also show more complex hygroscopic behaviors. We produced various types of nanoparticles of NaCl, (NH4)SO4, H2SO4, organic acid, soot, and their internal mixtures by using an atomizer, a furnace reactor, and a laser ablation reactor, and the hygroscopic properties of size-selected nanoparticles are measured with the NanoTDMA technique. Preliminary results for hygroscopic properties of NaCl nanoparticles showed that for particles of 10, 15, and 20 nm, their GF (Growth Factor) decreased and DRH (Deliquescence RH) increased compared to those of 30 nm particles, independent of generation methods. The NaCl particles produced by the furnace reactor system (evaporation-condensation method) initially shrunk with increasing RH below the DRH, while those produced by the atomizer showed no such shrinkage. TEM images of the furnace reactor-generated nanoparticles suggest that these particles are loose aggregates consisting of small NaCl crystals, probably restructuring into compact aggregates with increasing RH.
Ultrafine particles nanoparticles NanoTDMA hygroscopicity volatility
Kihong Park Jae-Seok Kim
Department of Environmental Science and Engineering, Gwangju Institute of Science and Technology, Gwangju, Korea
国际会议
天津
英文
13-15
2007-07-17（万方平台首次上网日期，不代表论文的发表时间）