STUDY OF DYNAMIC BEHAVIOR OF NANOMETER-SIZED AEROSOL PARTICLES AND ION CLUSTERS

在本研究中，采用差分迁移率分析仪（DMA）结合冷凝核计数器（CNC）或静电计（EM）作为粒子检测器，研究了纳米级气溶胶粒子和离子簇的动力学行为。所得结果可总结如下。在第一年，进行了一项理论和实验研究，研究了在使用DMA进行气溶胶尺寸测量时，在需要低电场进行分类的极细颗粒情况下的迁移率变化。结果表明，迁移率的变化是由于(i)不同大小粒子轨迹的扩散混合，以及（ii）除了施加的场之外还存在空间电荷场。此外，最重要的结果可以总结如下：(i)小于平均值的粒子在小于理想电压下被分类；（ii）大于平均值的粒子在大于平均值的电压下被分类。（iii）较大的气溶胶浓度导致较大的位移；（iv）即使在低气溶胶浓度下，由于布朗扩散效应，迁移率也会发生变化；(v)移动性变化仅在第一个DMA中重要，而在第二个DMA中可以被安全地忽略。在第二年，使用串联DMA系统进行粒度测量，在第一年结果的基础上准确确定颗粒的大小。研究了纳米颗粒通过丝网和层流管的渗透过程。得到的结果可以总结为：(1)粒子中电荷的存在不影响它们的穿透行为；（ii）现有的理论，如Cheng和Yeh的丝网理论和Gormley和Kennedy的电子管理论，对于斯托克斯-爱因斯坦直径小于2nm的粒子是准确的；(3)颗粒不会从金属表面反弹，即所有颗粒-金属碰撞都是有效的。此外，进行了双极性空气离子对气溶胶颗粒的充电和中和实验研究。结果表明，如果选择合适的离子迁移率和质量值，对于大于3nm的粒子，我们的实验结果与Fuchs理论非常吻合。在3nm以下的尺寸范围内，偏差是相当大的和突然的。少

In this research, dynamic behavior of nanometer-sized aerosol particles and ion clusters was studied by measuring with the differential mobility analyzer (DMA) combined with a condensation nucleus counter (CNC) or an electrometer (EM) as a particle detector. The results obtained can be summarized below. At the first year, a theoretical and experimental study of mobility shift in the case of extremely fine particles requiring low electric fields for their classification when performing aerosol size measurements with the DMA has been carried out. As a result, it was made clear that the mobility shift is due to (i) diffusive mixing of trajectories of different-sized particles, and (ii) the existence of a space-charge field in addition to the applied field. Furthermore, the most important results can be summarized thus : (i) particles smaller than the average are classified at voltages smaller than the ideal ; (ii) particles larger than the average are classified at voltages larger than th … More e ideal ; (iii) larger aerosol concentrations lead to larger shifts ; (iv) mobility shifts occur even at low aerosol concentrations due to Brownian diffusion effects ; and (v) mobility shifts are important only in the first DMA,and can be safely neglected for the second. At the second year, particle size measurement were done using a tandem DMA system to accurately determine the size of the particles on the basis of the results of the first year. Penetration of nanometer-sized particles through a wire screen and a laminar flow tube has been carried out. The results obtained can be summarized thus : (i) the presence of electrical charges in the particles do not affect their penetration behavior ; (ii) the existing theories, Cheng and Yeh for wire screens and Gormley and Kennedy for tubes, are accurate for particles with Stokes-Einstein diameter down to 2nm ; and (iii) particles do not rebound from the metallic surfaces, i.e., all the particle-metal collisions are effective, Furthermore, an experimental study of charging and neutralization of aerosol particles by bipolar air ions has been carried out. As a result, if adequate value of ion mobility and mass are chosen, our experimental results agree very well with Fuchs'theory for particles larger than about 3nm. In the size range below 3nm, deviations are considerable and abrupt. Less