A DMA Train for Precision Quantification of Nanoparticle Growth Rates in the sub-10 nm Size Range

Measurements of nanoparticle growth rates in the sub-10nm size range are difficult to perform due to high particle losses and low detection efficiencies, especially below 3nm. Also time resolution of conventional SMPS limits the quantitative evaluation of growth rates (Winkler et al (2012), Geophys. Res. Lett. 39, L20815).

Here we present the development of a Differential Mobility Analyzer-Train (DMA-Train) operating six DMAs in parallel for high time resolution quantification of nanoparticle growth rates down to 1.5 nm. To this end, each DMA channel is operated at a fixed voltage allowing precise measurement of the evolution of individual particle sizes. For the detection of classified particles we use five butanol based condensation particle counters (CPC) (TSI3776) and one water based CPC (TSI3788). For the smallest size channels at 2 nm and below, two Airmodus A10 particle size magnifiers (PSM) (Vanhanen et al. (2011), Aerosol Sci. Technol. 45, 533) are used. The setup follows the classical scanning mobility particle sizer (SMPS) design but with six distinct channels. Therefore no voltage adjustment at the DMA is necessary during standard operation. This provides a much higher time resolution by avoiding voltage scanning and signal retention due to voltage changes. Furthermore, the data inversion procedure for the extraction of the spectral data is simplified and a full statistical approach is used to determine the growth rates, significantly reducing measurement uncertainties.