Accurate field characterization of aerosol number density, extinction cross-section, mass extinction, and aerosol mass concentration is of basic importance in the development of improved smoke screens and electro-optical weapons systems. During a recent field test involving smoke screen tests, data were obtained from 1) a spectral transmissometer which measured transmittance once per second for 200 wavelengths between 2.5 and 14 micrometres, 2) optical particle size analyzers, 3) an electric cascade impactor, 4) a quartz crystal microbalance, and 5) mechanical mass samplers. The aerosol parameters of interest (number density, extinction cross-section, etc.) were computed through combinations of independently measured parameters in order to determine data consistency and the spread in values which might be encountered from such measurements. Results obtained from some of these instruments are described which show how the mass extinction coefficient can be expected to vary with time. It is shown that this time dependence is a major reason for wide variability in field measurements of the extinction coefficient.