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

本研究采用差示迁移率分析仪(DMA)结合凝聚核计数器(NC)或静电计(EM)作为粒子探测器，对纳米气溶胶粒子和离子团簇的动态行为进行了研究。所获得的结果可以总结如下。在第一年，在用DMA进行气溶胶尺寸测量时，对需要低电场进行分类的极细颗粒的迁移率漂移进行了理论和实验研究。结果表明，迁移率漂移是由于(I)不同大小粒子轨迹的扩散混合，以及(Ii)除了外加电场外，还有空间电荷场的存在。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时被分类；(Ii)大于平均值的粒子在大于Th…的电压下被分类(3)较大的气溶胶浓度会导致较大的迁移；(4)由于布朗扩散效应，即使在低浓度的气溶胶中也会发生迁移；以及(5)迁移迁移仅在第一个DMA中很重要，对于第二个DMA可以安全地忽略。在第二年，使用串联DMA系统进行颗粒尺寸测量，以根据第一年的结果准确地确定颗粒尺寸。在金属丝网和层流管内实现了纳米颗粒的穿透。所得结果可概括为：(I)粒子中电荷的存在不影响其穿透行为；(Ii)现有的理论，如线网理论、Gormley和Kennedy理论，对于Stokes-Einstein直径为2 nm的粒子，都是精确的；(Iii)粒子不会从金属表面反弹，即所有粒子-金属碰撞都是有效的。此外，还进行了双极空气离子对气溶胶粒子荷电和中和的实验研究。因此，如果选择适当的离子迁移率和质量值，对于大于3 nm的粒子，我们的实验结果与Fuchs的理论非常吻合。在小于3 nm的尺寸范围内，偏差是相当大和突然的。较少

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