Characterization of a high-resolution supercritical differential mobility analyzer at reduced flow rates

Abstract

Classifying sub-3 nm particles effectively with relatively high penetration efficiencies and sizing resolutions is important for atmospheric new particle formation studies. A high-resolution supercritical differential mobility analyzer (half-mini DMA) was recently improved to classify aerosols at a sheath flow rate less than 100 liters per minute (lpm). In this study, we characterized the transfer functions, the penetration efficiencies, and the sizing resolution of the new half-mini DMA at the aerosol flow rate of 2.5-10 lpm and the sheath flow rate of 25-250 lpm using tetra-alkyl ammonium ions and tungsten oxide particles. The transfer functions of the new half-mini DMA at an aerosol flow rate lower than 5 lpm and a sheath flow rate lower than 150 lpm agree well with predictions using a theoretical diffusing transfer function. The penetration efficiencies can be approximated using an empirical formula. When classifying 1.48 nm molecular ions at an aerosol-to-sheath flow ratio of 5/50 lpm/lpm, the penetration efficiency, the sizing resolution, and the multiplicative broadening factor of the new half-mini DMA are 0.18, 6.8, and 1.11, respectively. Compared to other sub-3 nm DMAs applied in atmospheric measurements (e.g., the mini-cyDMA, the TSI DMA 3086, the TSI nanoDMA 3085, and the Grimm S-DMA), the new half-mini DMA characterized in this study is able to classify particles at higher aerosol and sheath flow rates, leading to a higher sizing resolution at the same aerosol-to-sheath flow ratio. Accordingly, the new half-mini DMA can reduce the uncertainties in atmospheric new particle formation measurement if coupled with an aerosol detector that could work at the corresponding high aerosol flow rate.

Precision characterization of three ultrafine condensation particle counters using singly charged salt clusters in the 1–4 nm size range generated by a bipolar electrospray source

“…Aerosol standards with nanometer dimensions for instrument calibration are produced by means of electrospray generation. Previous studies (Kangasluoma et al 2013;Ude and Fern andez de la Mora 2005) have demonstrated that solutions of tetra-alkyl ammonium halides are well-suited for the clean generation of mobility standards at inverse mobilities below 2 Vs/cm 2 for instrument calibration (Cai et al 2018;Jiang et al 2011). It should be noted though that the mobility spectra for cluster ions electrosprayed from tetra-alkyl ammonium halides are dominated by larger multiply charged clusters leading to a too pronounced background to distinguish mobility peaks of singly charged clusters (Attoui et al 2013).…”

Parameters governing the performance of electrical mobility spectrometers for measuring sub-3 nm particles

“…A miniature cylindrical DMA operating at a medium sheath flow rate (20-30 liters per minute) was developed to improve the penetration efficiency and size resolution for sub-3 nm particles (Cai et al 2017a). A supercritical DMA working at reduced aerosol and sheath flow rates (Cai et al 2018a; Fernández de la Mora 2017) was recently applied to improve the size resolution of a differential mobility particle spectrometer (Kangasluoma et al 2018).…”

Activation of sub 2 nm Water Soluble and Insoluble Standard Ions with Saturated Vapors of Butanol in a Boosted TSI ultrafine CPC

“…The experimental setup is the classical setup and method used during the last few decades for the generation of sub-10 nm and detection-efficiency measurements with a high particle size resolution. It is widely documented in the literature [25,[42][43][44][45][46][47]. The high resolution generator is a combination of a home-made electrospray source [22] and a high resolution Attoui-type DMA [44].…”