Measurement of Unipolar Charged Aerosol Particles Using a Long Electrical Mobility Spectrometer
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In this work, a long electrical mobility spectrometer (EMS) was developed for measuring the unipolar charge of aerosol particles. The long EMS consists of three main parts: a particle charger, a long multi-channel size classifier column, and a multi-channel electrometer. Particle charging is carried out by exposing an aerosol sample to a cloud of unipolar corona ions inside the corona-needle charger, and then charged via ion to particle collisions. The charged aerosol passes into the multi-channel size classifier column, configured as coaxially cylindrical electrodes. A DC high voltage is applied to the inner electrode, while the outer electrode is grounded. There are two separate streams, aerosol and sheath air flows. The charged aerosols enter the size classifier column. A high electric field formed between the electrodes makes the particles deflected radially outward and particles having specific mobility are collected on electrically isolated electrometer rings, positioned at the inner surface of the outer electrode. A multi-channel electrometer connected to these electrometer rings measures signal currents corresponding to the unipolar charge of aerosol particles of a given mobility which is related to the particle size. The performance of this long EMS was evaluated using polydispersed, carbonaceous aerosol particles generated by a diffusion flame, combustion aerosol generator (CAG). Preliminary test results showed that the long EMS performed well and was a valuable tool available for measuring unipolar charge of aerosol particles.
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