Tandem aerodynamic aerosol classifier – differential mobility analyzer as a single charged aerosol source for diameters up to one micrometer

This work describes a method to generate monodisperse, spherical, single-charged aerosols for instrument calibration in the size range of 32 – 1000 nm using an aerodynamic aerosol classifier (AAC) and differential mobility analyzer (DMA) in series. The AAC is used to input a monodisperse aerosol into the DMA to reduce the fraction of larger multiple charged particles exiting the DMA. The method produces test aerosols over a wide size range with less than 1% multiple charging and in concentrations between 4,000 – 10,000 particles/cm3 at more than 2 liters/minute flow rate, sufficient to be measured with the aerosol electrometer and condensation particle counter (CPC). At diameters between 32 nm and 1000 nm, the multiple charging was less than 0.1%. Operating parameters for the AAC and DMA are provided, along with CPC detection efficiencies up to 1000 nm measured with traceability to the international system of units. Use of the AAC allows for calibrations to be performed over almost the full particle diameter range of the DMA with an easily reproduced experimental setup using commercially available equipment.