PREDICTIONS OF FACTORS AFFECTING EXTINCTION EFFICIENCIES OF INTERNALLY MIXED AEROSOLS USING THE REIST-WILSON-MARS PROGRAM

A program that combines the MARS code (Saxena et al. 1986, Atmos. Envi r. 20, 1471-1483) with a code for calculating optical properties of ae rosols is used to predict scattering and absorbing efficiencies of sec ondary aerosols as a function of chemical composition, relative humidi ty, temperature, and size distribution parameters of the aerosols. The predictions are compared with empirical data from the literature. Sca ttering and absorbing efficiencies are mixture-specific and not specie s-specific; thus they can be used for determining visibility budgets o nly in a specific geographical location and under specific meteorologi cal conditions. Estimation of scattering and absorbing efficiencies ob tained from regression analysis and deterministic methods do not diffe r significantly. The relative abundances of sulfates and nitrates do n ot affect scattering efficiencies much. The presence of an absorbing s pecies causes even non-absorbing species such as sulfates and nitrates to have an absorption efficiency. The real part of the refractive ind ex does not affect the absorption efficiency; however, the imaginary p art of the refractive index does affect the scattering efficiency of t he bulk aerosol. Copyright (C) 1996 Elsevier Science Ltd.