RADIOMETRIC MODEL OF THE TRANSMISSION CELL-RECIPROCAL NEPHELOMETER

A radiometric model has been developed to assess the effects of angular truncation, finite size of the detector, and angle response characteristics of the cosine sensor on the measurement of the total scattering coefficient by a transmission cell-reciprocal nephelometer. These effects are computed for monodisperse polystyrene spheres over the size range 0.02-8 mum based on Mie theory and for smoke agglomerates ranging from 10 to 10(7) primary units based on the Fisher-Burford approximation. The accuracy of the model calculations is determined by comparison with exact solutions for the case of a detector with an infinitesimal area and for a finite area detector with a diffuse scattering function. The predicted results are compared with measured results for six different sizes of monodisperse polystyrene sphere aerosols with particle diameters in the range 0.1-2.35 mum. The measurements were carried out as a function of the distance between the laser beam and detector for 1.3 and 2.7 cm diameter cosine sensors. A table of design parameters for making accurate total scattering measurements is obtained for both spheres and agglomerates. An accuracy of +/-5% was obtained for spherical particles with diameters less-than-or-equal-to 1.1 mum with our TCRN, and we estimate that similar performance would be obtained for smoke agglomerates with up to 3 x 10(3) primary spheres per agglomerate.