Transfer function and transmission measurements of the Perez differential mobility analyzer (DMA) at moderate sheath flow rates

Abstract

The newly developed Perez Differential Mobility Analyzer (DMA) provides high size resolution for viral particles and similarly sized particles. In this study, we measured its transfer function and transmission at moderate sheath flow rates (from 20 to 100 L min⁻¹) to extend its application for the measurement of broader sized particles. Two DMAs—a Perez Fat DMA and a Perez Thin DMA, were first calibrated using tetraheptylammonium bromide monomer (THA⁺) at sheath flow rates ranging from 100 to 400 L min⁻¹. Subsequently, a tandem Perez DMA setup was constructed. The former DMA was operated at high sheath/aerosol flow rate ratios to classify metal particles sized between 10 and 30 nm with a high resolution. The latter DMA was operated at moderate sheath flow rates ranging from 20 to 100 L min⁻¹. Particles classified by the former DMA were assumed monodispersed and used to calibrate the latter one. The measured transfer function for 10 nm particles was only slightly broader than the theoretical transfer function, with broadening factors of f_σ = 1.39 for the Perez Thin DMA and 1.28 for the Perez Fat DMA. The Perez Thin DMA exhibited higher resolutions than the Perez Fat DMA. For 20 nm particles, the Perez Thin DMA achieved a size resolution exceeding 8 at a sheath/aerosol flow rate ratio of 20/2 and over 11 when the ratio increased to 100/5. The penetration efficiencies of 10–30 nm particles were higher than 72.6%, with the Perez Fat DMA having higher penetration efficiencies than the Perez Thin DMA. Decreasing penetration efficiencies were observed under higher sheath flow rates, likely due to minor flow turbulence and changes in the electric field at the DMA outlet, which contributed to particle losses. After calibration, the Perez Fat DMA was adapted to measure the size distributions and charging properties of metal particles produced in a wire generator. At moderate sheath flow rates, Perez DMAs provide an extended size measurement range, high size resolution, and excellent penetration efficiency.