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 m p and effective density r eff distributions of particles with a specific electrical mobility diameter d m . Combinations of these instruments, which are referred to as the DMA-APM or DMA-CPMA system, are also used to quantify the massmobility exponent D m 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(m p )-log(d p ) space. A theoretical analysis of the DMA-APM transfer function demonstrated that the resolution of the setup is maintained when the rotation speed v of APM is scanned to measure distribution. In addition, an equation was derived to numerically calculate the minimum values of the APM resolution parameter λ c for eliminating multiple charged particles.

New approaches to calculate the transfer function of particle mass analyzers

“…At the same time, particles with different properties can diffuse into the center of the gap and exit the device, such that the transfer function widens. The shape of the APM transfer function is consistent with previous calculations by Ehara , Hagwood, and Coakley (1996) and Kuwata (2015) as discussed in the SI.…”

“…is often used to characterize a particle mass analyzer and determines the shape of the transfer function (Olfert and Collings 2005;Ehara, Hagwood, and Coakley 1996;Kuwata 2015). In this case, F is easily invertible, such that a closed form can be determined for G 0 : Figure 4 shows the transfer function resulting from this treatment for the CPMA and APM settings given in Table 1 and m à ¼ 10 fg (corresponding to D 0 ¼ 8.4  10 À4 , such that diffusion is negligible).…”

Practical limitations of aerosol separation by a tandem differential mobility analyzer–aerosol particle mass analyzer

“…Prior studies have only considered particles bearing a single net charge (Barone et al 2011; Lall et al 2008; Lin et al 2014; Olfert 2005; Tajima et al 2011; Tajima et al 2013). A recent modeling study by (Kuwata 2015) did consider the effects of multiply charged particles in a tandem DMA-APM measurement. However, only a single combination of transfer functions was considered for a given set of conditions instead of the convolution of transfer functions as is required; see ensuing discussion or (Lall et al 2009).…”

Effects of temperature, pressure, and carrier gases on the performance of an aerosol particle mass analyser

“…6. It should be noted that, according to the work done by Kuwata (2015), even when the resolution of the DMA-APM system appears to be controlled by the APM, the particle classification by the DMA-APM at a certain operating condition still could be regulated by both DMA and APM.…”

“…According to Kuwata's theoretical analysis of transfer function and resolution of the DMA-APM system, the common operation of constant ω and varying V could not maintain the transfer function because of the range of d p,m passing the DMA (Kuwata, 2015). In such a case, the transfer function may not be symmetric, and the transfer function is narrower for larger m because of the dependence of λ c on m. It was then concluded that the operation of constant V and varying ω, on the other hand, could better maintain the DMA-APM resolution because mω 2 can be constant under constant V .…”