Aerosol Size Distribution Measurement Using Multi-Channel Electrical Mobility Sensor

Abstract

Aerosol particles can be classified according to their electrical mobility. A multi-channel detector has been developed to classify electrically charged airborne particles under the influence of an electric field. The detector is capable of measuring the electrical mobility of particles in the sub-micrometer size range. It is compactly designed as an assembly of two concentrically-aligned cylindrical short electrodes with a fixed clearance. Sheath air and aerosol flows enter from one end, pass through the annulus and exit the other end. An electric field is applied between the inner and outer electrodes. Particles with a given electrical mobility are collected on a designated electrometer ring where electrical signals are measured to obtain size distributions. In this study, a mathematical model was developed to optimize the locations of particle detection sensors and the calculations of particle trajectories were performed for various particle sizes. A prototype detector constructed in the present work gave the particle sizes which are in good agreement with those obtained by a scanning electron microscope. Signal current from the detector was also analyzed to give number concentration of particles. Experimental results agreed well with the theoretical predictions. The proposed model was proven to be useful in designing the detector and the prototype detector showed promising results for aerosol size measurement.