Abstract. Accurate particle classification plays a vital role in
aerosol studies. Differential mobility analyzers (DMAs), centrifugal particle
mass analyzers (CPMAs) and aerodynamic aerosol classifiers (AACs) are commonly
used to select particles with a specific mobility diameter, aerodynamic
diameter or mass, respectively. However, multiple charging effects cannot be
entirely avoided when using either individual techniques or tandem systems
such as DMA–CPMA, especially when selecting soot particles with fractal
structures. In this study, we calculate the transfer functions of the
DMA–CPMA and DMA–AAC in static configurations for flame-generated soot
particles. We propose an equation that constrains the resolutions of the DMA and
CPMA to eliminate the multiple charging effect when selecting particles with
a certain mass–mobility relationship using the DMA–CPMA system. The equation
for the DMA–AAC system is also derived. For DMA–CPMA in a static
configuration, our results show that the ability to remove multiply charged
particles mainly depends on the particle morphology and resolution settings
of the DMA and CPMA. Using measurements from soot experiments and literature
data, a general trend in the appearance of the multiple charging effect with
decreasing size when selecting aspherical particles is observed. As for
DMA–AAC in a static configuration, the ability to eliminate particles with
multiple charges is mainly related to the resolutions of the classifiers. In
most cases, the DMA–AAC in a static configuration can eliminate the multiple
charging effect regardless of the particle morphology, but multiply charged
particles will be selected when decreasing the resolution of the DMA or AAC.
We propose that the potential influence of the multiple charging effect
should be considered when using the DMA–CPMA or DMA–AAC systems in
estimating size- and mass-resolved optical properties in field and lab
experiments.