Development of a Multiple-Stage Differential Mobility Analyzer (MDMA)

Abstract

A new DMA column has been designed with the capability of simultaneously extracting monodisperse particles of different sizes in multiple stages. We call this design a multistage DMA, or MDMA. A prototype MDMA has been constructed and experimentally evaluated in this study. The new column enables the fast measurement of particles in a wide size range, while preserving the powerful particle classification function of a DMA. The prototype MDMA has three sampling stages, capable of classifying monodisperse particles of three different sizes simultaneously. The scanning voltage operation of a DMA can be applied to this new column. Each stage of MDMA column covers a fraction of the entire particle size range to be measured. The covered size fractions of two adjacent stages of the MDMA are designed somewhat overlapped. The arrangement leads to the reduction of scanning voltage range and thus the cycling time of the measurement. The modular sampling stage design of the MDMA allows the flexible configuration of desired particle classification lengths and variable number of stages in the MDMA. The design of our MDMA also permits operation at high sheath flow, enabling high-resolution particle size measurement and/or reduction of the lower sizing limit. Using the tandem DMA technique, the performance of the MDMA, i.e., sizing accuracy, resolution, and transmission efficiency, was evaluated at different ratios of aerosol and sheath flowrates. Two aerosol sampling schemes were investigated. One was to extract aerosol flows at an evenly partitioned flowrate at each stage, and the other was to extract aerosol at a rate the same as the polydisperse aerosol flowrate at each stage. We detail the prototype design of the MDMA and the evaluation result on the transfer functions of the MDMA at different particle sizes and operational conditions.

A cost-effective differential mobility analyzer (cDMA) for multiple DMA column applications

“…The transfer function of a DMA is best obtained by the Tandem DMA (TDMA) technique (Chen et al, 2007;Fissan et al, 1996;Hummes et al, 1996). In this study, we used the same technique to evaluate the performace of the cDMAs.…”

“…A numerical optimization scheme was applied to vary the values of the parameters simultaneously, minimizing the difference between the measured and calculated TDMA curves. The same deconvolution scheme has been applied to obtain the real transfer function of the Nano-DMA (Li et al, 2006) and MDMA (Chen et al, 2007). Fig.…”

“…Multi-electrode DMAs (Mirme, 1994;Tammet et al, 2002) were also developed to reduce the DMA measurement time from minutes to a fraction of a second. Further, a multi-stage DMA (MDMA) was designed to extract monodisperse particles of different sizes at the same time (Chen et al, 2007). The MDMA not only covers a wide sizing range but also improves the DMA measuring cycle by varying the voltage in sub-sections of the entire sizing range.…”

Experimental evaluation of miniature plate DMAs (mini-plate DMAs) for future ultrafine particle (UFP) sensor network

“…Tandem DMA (TDMA) technique, in which two DMAs are operated in series, was applied in the performance evaluation (Rader and McMurry 1986;Fissan et al 1996;Hummes et al 1996;Chen et al 2007). One of two calibrated DMAs (TSI Model 3081 and 3085) was used as the 1st DMA to classify monodisperse NaCl particles in selected sizes.…”

“…A numerical optimization scheme was used to find best-fitted TDMA data to the experimental one in order to retrieve the unknowns. The same deconvolution scheme has been applied to obtain the real transfer function of nano-DMA (Li et al 2006), multiple-stage DMA (MDMA; Chen et al 2007), and cDMA (Mei et al 2011). …”