Size Measurement of Airborne Particulates by Time-of-Flight Spectroscopy

Abstract

The use of time-of-flight spectroscopy for measuring the aerodynamic size distribution of airborne particulates expanded into an aerosol beam in a vacuum environment is described. Results obtained using two different prototype models are presented. Both of these instruments use scattered light signals generated by the passage of a sample particle through one or two focused laser beams to detect and measure the particles. Although convenient to use for larger particles, the intensity of the scattered light signals depends very strongly on particle size so that particles smaller than about 0.1 µm diameter cannot be detected and measured. The detection of sample particles by electron beam scattering is considered in detail. By use of this detection method, it seems possible to extend the range of measurable particle size to an order of magnitude smaller.