An Electrical Mobility Spectrometer for Aerosol Size Distribution Measurement

Abstract

Accurate measurements of aerosol size distribution are desirable in order to investigate atmospheric aerosol processes. In the present paper, an electrical mobility spectrometer for measurement of numberweighted particle size distribution in sub-micrometer size range is described. The spectrometer consists of a size selective inlet, an aerosol charger, an electrostatic classifier, a signal detection system, a flow arrangement system and a computer controlled interface system. Particle charging is accomplished by exposing aerosol sample to the cloud of unipolar corona ions, and then charged via ion-particle collisions. The charged aerosol passes into the electrostatic classifier, configured as coaxially cylindrical electrodes. There are two separate streams, aerosol and sheath air flows. The charged aerosols enter the analyzer column. They are then deflected radially outward and collected on electrically isolated electrometer rings, positioned at the inner surface of the outer electrode. Electrometers connected to these electrode rings measure currents corresponding to the number concentration of particles of a given mobility which is related to the particle size. Signal currents are then recorded and processed by a data acquisition system. A prototype of the spectrometer was built and experimentally tested. From preliminary test results, the spectrometer has been found to be promising for determining particle size distribution.