RESOLUTION OF THE RADIAL DIFFERENTIAL MOBILITY ANALYZER FOR ULTRAFINEPARTICLES

The resolution of the radial differential mobility analyzer (radial DM A) for particles in 3-60 nm diameter range is probed through tandem ra dial DMA measurements employing identical radial DMAs. The observed br oadening of the range of transmitted particles with decreasing particl e Peclet number was shown to be consistent with Stolzenburg's (1988, P h.D. Thesis, University of Minnesota)model of diffusion broadening of the transfer function, although the broadening was somewhat greater th an predicted. A similar, but smaller, deviation is seen in Stolzenburg 's data obtained using a cylindrical DMA. The enhanced broadening is t hought to result from flow disturbances within the DMA. Diffusional de position of particles in the radial DMA for two different sheath flow rates correlated well with Pe(-2/3), while electrophoretic particle lo sses in the transition from high voltage at the outlet of the DMA to g rounded tubing are shown to be independent of the particle Peclet numb er. The latter effect is, however, small for the radial DMA. Consisten t with observations previously made using cylindrical DMAs, the voltag e corresponding to the peak in the number concentration is slightly hi gher for the second DMA than for the first one. This apparent decrease in mobility correlates with Pe(-1). Copyright (C) 1996 Elsevier Scien ce Ltd