AN INSTRUMENT FOR THE CLASSIFICATION OF AIRBORNE PARTICLES ON THE BASIS OF SIZE, SHAPE, AND COUNT FREQUENCY

A laser light scattering instrument for the study of airborne particulate material is described. The instrument examines individual particles (primarily in the size range 1-10-mu-m equivalent diameter) at rates of up to 10,000 s-1. Each particle is ascribed an asymmetry factor, or asphericity factor, based upon the spatial intensity distribution of the scattered laser radiation. This factor ranges from 0 for perfect spheres to 100 for long fibres. Particles are also ascribed a size parameter based upon the total equivalent scattering from a perfect sphere. Data may be displayed graphically in terms of size vs count frequency, asymmetry factor vs count frequency, or as an axonometric plot of size vs asymmetry factor vs count frequency. The latter three-dimensional surface is a characteristic signature of the aerosol under examination and preliminary results indicate the possibility of employing this form of data analysis to monitor small changes in aerosol composition, such as, for example, the presence of low concentrations of spheres (droplets) or fibres. Results are presented for incompressible solid spheres, liquid droplets, and mineral fibres.