Abstract
Three commercially available instruments that use Mie light scattering were studied; two forward light scattering aerosol photometers, and a right-angle scattering particle counter. Standard calibration aerosols may be different from aerosols encountered at test locations, though made to appear similar by the instrument measurements. Modifications to the right-angle scattering particle counter, necessary to adapt it to the high dust loadings in studies other than aerosol-free environments, cause substantial errors in the measured particle size distribution. Frequent checking by optical and electron microscopy is essential to identify the actual particle-size distribution of the aerosol.