[en] For large-scale testing of sodium-fire aerosols, no off-the-shelf instrument is available for accurate measurement of the particle size distribution function in the diameter region from 0.5 - 30 m. In the long range, cascading impactors are considered to be most suitable for in-situ measurement of sodium-fire aerosols because of simplicity of operation and maintenance. The calibration of cascading impactors can be best carried out by a combined use of the centrifuge (for particles with diameter range from 0.5 - 5 m) and by direct observation with a microscope (for particles ranging from 5 - 30 m). Three distinctly different characteristics are found. To avoid the complex problem of controlling the chemical composition of the sodium-fire aerosol during and after the particle generation, it is best to analyze the aerosol by first classifying the particles according to their size - with either a centrifuge or a cascading impactor - and then to determine the chemical composition of the particles in each size range by electron diffraction technique. Very limited information is available at the present time for the particle size distribution measurement in the diameter range 5 - 30 m