Size selection of sub-and super-micron clay mineral kaolinite particles using a custom-built Maxi-DMA

Number size distribution measurements for sub-and super-micron kaolinite particle were performed with a custom Maxi-Differential Mobility Analyzer (Maxi-DMA) built at the Leibniz Institute for Tropospheric Research (TROPOS). The Maxi-DMA can select larger diameters (500 nm to 3000 nm) than common DMAs (50 nm to 800 nm). Particles used in this study were generated with a medical nebulizer, dispersing kaolinite and monodisperse polystyrene latex (PSL) suspensions. Behind the Maxi-DMA, particles were counted with a condensation particle counter (CPC 3010, TSI) and/or an aerodynamic particle sizer (APS 3321, TSI). Utilizing a cyclone with adjustable aerodynamic cut-off diameters (D50) upstream the Maxi-DMA, it was possible to largely reduce the presence of multiply charged larger particles downstream of the Maxi-DMA. With this set-up it is possible to provide size selected particles in the super-micron size range with stable particle number concentrations and a low fraction of multiply charged particles for f...