Particle classification by the tandem differential mobility analyzer-particle mass analyzer system

Abstract

Particle mass analyzers, such as the aerosol particle mass analyzer (APM) and the Couette centrifugal particle mass analyzer (CPMA), are frequently combined with a differential mobility analyzer (DMA) to measure particle mass mp and effective density ρeff distributions of particles with a specific electrical mobility diameter dm. Combinations of these instruments, which are referred to as the DMA-APM or DMA-CPMA system, are also used to quantify the mass-mobility exponent Dm of non-spherical particles as well as to eliminate multiple charged particles. This study investigates the transfer functions of these setups, focusing especially on the DMA-APM system. The transfer function of the DMA-APM system was derived by multiplying the transfer functions of DMA and APM. The APM transfer function can be calculated using either the uniform or parabolic flow models. The uniform flow model provides an analytical function, while the parabolic flow model is more accurate. The resulting DMA-APM transfer functions were plotted on log(mp)-log(dp) space. A theoretical analysis of the DMA-APM transfer function demonstrated that the resolution of the setup is maintained when the rotation speed ω of APM is scanned to measure distribution. In addition, an equation was derived to numerically calculate the minimum values of the APM resolution parameter λc for eliminating multiple charged particles.