Aerosol sizing by laser Doppler relaxation-time measurement

Methods using laser Doppler velocimeters have been developed for measuring the dynamic relaxation time (τ p ) of aerosol particles and droplets. For real-time measurement of aerodynamic size spectra in the range of 0.2-50.0 μm in diameter, the most promising methods employ (1) acoustic excitation, for the size range of 0.2-5.0 μm in diameter, and (2) gravity settling, for the size range of 5.0-50.0 μm in diameter. Both methods have been applied to rapid in situ measurement of the size distribution of stable and unstable aerosols. Experimental results indicate that these newly developed methods compliment the existing methods of real-time aerosol size analysis.