Unipolar charging based, hand-held mobility spectrometer for aerosol size distribution measurement

Abstract

A hand-held particle size spectrometer for monitoring workplace exposure to aerosols and nanoparticles with 13 channels in the 15–630nm has been described. The instrument uses electrical mobility-based size classification in which aerosol particles are electrically charged using a unipolar corona charger, followed by classification in a condenser-type disk classifier, and particle counting using a commercial handheld condensation particle counter (CPC; Model 3007, TSI Inc., Shoreview, MN). A unipolar charger was designed to reduce multiple charging of particles which helped extend the measurable size range. The electrical classifier, which served as a low-pass mobility filter, was operated at 2:1 sheath-to-aerosol flow ratio using a single pump inside the CPC. An inversion scheme was developed to obtain discrete size distributions from cumulative mobility distributions. The sizing accuracy was also experimentally investigated using DMA-classified, near-monodisperse particles and was found to be in the range 1.4–8.1% below 300nm, and increased to 13.6% for 500nm particle. Experimentally measured sizing uncertainties ranged from 78–114%. The counting uncertainties of the instrument were in the range 0.1–10.5% for typical concentration range for ambient and workplace aerosols. Size distributions of test unimodal and bimodal polydisperse aerosols measured using HPSS agreed reasonably well with that from the laboratory scanning mobility spectrometer. HPSS can be useful in many routine monitoring applications, though the measured uncertainties can be large for some applications.