Particle size evaluations using multiwavelength extinction measurements

As the first phase of a program to develop a lidar method for remote evaluation of mean particle size of stationary source emissions, a data base was experimentally collected consisting of multiple-wavelength extinction coefficients and mean particle sizes of generated aerosols. Extinction data were collected using multi-wavelength (14) transmissometers and a 10-m long aerosol tunnel facility. Generated aerosols consisted of five size fractions of fly ash, three size fractions of silica, and single-size fractions of six other types of particulate material. Particle size evaluations were made by multistage impactor and by air permeability (Fisher) analysis of packed powder. The data base indicates that mean particle size smaller than l-microm diam could be estimated usefully from aerosol extinction measurements using a single-laser lidar system operating at 1.06- and 0.53-microm wavelengths. For larger mean particle sizes the extinction ratio is near unity, and longer wavelength systems are required. The data indicate that a two-laser lidar operating at 10.6 and 0.53 microm could provide estimates of mean particle size to diameters of at least 6 microm.