ON THE SIZING ACCURACY OF LASER OPTICAL-PARTICLE COUNTERS

The performance of a narrow-angle and a wide-angle, forward scattering laser aerosol spectrometer has been studied as a function of particle size and refractive index. The results have been compared with theoretical calculations based on light scattering theory. The results indicate that for the narrow-angle instrument, the scattered-light intensity is not a monotonic function of particle size for transparent particles (a monotonic relationship is required for unambiguous particle size measurement) above 0. 7 mu m. The instrument is therefore limited in its useful range to size distribution measurement between 0. 2 mu m - its lower particle size limit - and 0. 7 mu m for transparent particles. In the case of the wide-angle instrument, the instrument output is a monotonic function of particle size for transparent particles, but the output is severely attenuated for light absorbing particles above 0. 3 mu m.