Differential Electrical Mobility Analysis: A Theoretical Study

Abstract

The subject of this work is the theoretical investigation of slowly scanning differential mobility analyzers (DMAs) which are, e.g., utilized to determine DMA transfer functions and to measure particle mobility distributions. A model to describe such systems is introduced and applied to investigate three different regimes of input mobiliw distributions: 1) a mobility distribution much narrower than the DMA transfer function, 2) a mobility distribution of about the same width as the DMA transfer function, and 3) a mobility distribution much wider than the DMA transfer function. Cases 1) and 2) are relevant for DMA transfer function measurements utilizing tandem differential mobility analyzer (TDMA) systems. For either regime, it is not possible to determine DMA transfer functions directly from the concentration distributions measured at the outlet of a DMA. For these cases, a deconvolution procedure is needed. Therefore, an iterative deconvolution procedure was developed. Determining DMA transfer functions utilizing the developed deconvolution procedure, different shapes of transfer function (triangular, Gaussian) are discussed. Case 3) is relevant for particle size distribution measurements. Here, the mobility distribution upstream of the DMA can be obtained by dividing the concentration distribution measured downstream of a DMA by the DMA transfer function area. The DMA transfer function area is influenced by diffusional losses inside the DMA, and therefore is size-dependent. Neglecting this size dependence results in an underprediction of particle number concentrations in the ultrafine particle size range. AEROSOL SCIENCE AND TECH-

Lightweight differential mobility analyzers: Toward new and inexpensive manufacturing methods

“…The height and full width at half maximum (FWHM) of the transfer functions of both DMAs determined by these measurements and the deconvolution scheme described by Stratmann et al (1997) are shown in Figure S4. Although the height and FWHM of the transfer functions of both DMAs as a function of particle size follow the same trend with the theory, the PU-DMA exhibits larger deviations compared to the SS-DMA.…”

“…The key parameters defining the transfer functions of the test DMAs were determined using the tandem DMA measurements and the deconvolution scheme described by Stratmann et al (1997). Figure 1 shows the normalized concentration of the charged tungsten particles (produced by the GW generator) measured by the PU-or the SS-DMA when set at different voltages and at b D 1.5/5.0.…”

Very Long DMA for the Generation of the Calibration Aerosols in Particle Diameter Range up to 10 µm by Electrical Separation

“…Usually a tandem-DMA setup is used (Birmili et al, 1997;Stratmann et al, 1997;Uin et al, 2006) for determining the DMA transfer function. Here, however, this method is not suitable, as in addition to the DMA under investigation, it requires the presence of another, identical or at least similarly capable DMA.…”

Technical Note: A New Deconvolution Scheme for the Retrieval of True DMA Transfer Function from Tandem DMA Data

“…All the existing deconvolution schemes, however, include presumed functional shapes for the DMA transfer function. The shape of the transfer function is often assumed to be either a triangle or a Gaussian shape (Hummes et al 1996;Stratmann et al 1997). From fundamental studies of DMAs (Stratmann et al 1995;Stolzenberg 1988), the triangular-shaped transfer function is best suited for nondiffusive particles, and the Gaussian-shaped one is better for highly diffusive particles.…”