Forwardscattering corrections for optical extinction measurements in aerosol media. 1: Monodispersions.

ABSTRACT

This paper, Part 1 of two papers, presents a parametric study of the forwardscattering corrections for experimentally measured optical extinction coefficients in homogeneous aerosol media, since some forwardscattered light invariably enters, along with the direct beam, into the finite aperture of the detector. Part 1 treats the case of monodispersions; Part 2, that of polydispersions. Forwardscattering is considered a single-scattering phenomenon, and the corrections are computed by two methods: one, using the exact Mie theory, and the other, the approximate Rayleigh diffraction formula. A parametric study of the dependence of the corrections on the particle size parameter, real and imaginary parts of the complex refractive index, and the half-angle of the detector's view cone has been carried out. The parameter ranges in which the results obtained by the approximate formulation agree well with those obtained by the Mie theory are also investigated. The agreement is especially good for small view cone angles and large particles and improves even more for slightly absorbing aerosol particles. Also discussed is the dependence of these corrections upon the experimental design of the transmission measurement systems.