Space-charge effects in the differential mobility analyzer

This paper presents a theoretical analysis of the effect of space-charge on the performance of differential mobility analyzers. The mathematical treatment. which is carried out for non-diffusing monodisperse aerosol particles, is based on the calculation of the electric field (applied plus space-charge) along particle trajectories, and leads to a simple expression for the classification voltage as a Function of two dimensionless parameters, The effect of aerosol properties (mobility, concentration), DMA geometry and operating conditions on the classification performance is discussed. The model predicts that space-charge affects the DMA performance for values of n(0)Z tau larger than about 22,000 V-1 cm(-1) (n(0) is the particle number concentration at DMA inlet; Z the electric mobility; tau the mean aerosol residence time). (C) 1999 Elsevier Science Ltd. All rights reserved.