Aerosols are known to influence the propagation of the solar radiation in the atmosphere. Aerosols emission sources are numerous: e.g. dust storms, fuel combustion (soot), ocean sprays, etc... Stratospheric aerosols and tropospheric anthropogenic aerosols which play an essential role in climate forcing (Charlson et al.¹) can be generated by atmospheric chemical reactions with sulfates, sulfuric acid and nitric acid. The volcanic eruptions are one of the important atmospheric aerosol generators, for example the eruption of the volcano Pinatubo, Philippines, June 1991 resulted in the emission 20 Mts of SO₂ (Gregs et al.²) which is a main source of sulfuric acid aerosol fraction.

Despite the large number of different aerosol sources, only some selected basic aerosol components have been considered in the development of various aerosol models (WMO publication³). Principal aerosol models (e.g. continental, urban, maritime, stratospheric, volcanic, upper atmosphere, and cloudy) and their basic components (e.g. dust, water-soluble particles, soot, salt particles (oceanic), sulfuric acid solution droplets, volcanic ash, and water) are listed in Table 1 (from Ref. 3) with the following entries:

• the aerosol model name (first column) and the related basic aerosol components (second column);

• the aerosol fraction by volume in % (third column), and the related aerosol relative concentration (fourth column), where N_i is the number of particles of the i-th component, and N is total number of particles in a given aerosol sample.

• the scattering coefficient:                                                                                     (1)

• the extinction coefficient:                                                                                     (2)

                                                                                            (3)

• the single scattering albedo:                                                                                                                     (4)

• the asymmetry factor:                                                                                                          (5)

• the normalization factor:                                                                                                                 (6)

is a linear interpolation of the phase function I_q..
Eqs. (1-5) determine optical properties of the aerosols to be considered in non-polarized radiative transfer problems. In particular, the optical thickness t(l) at the wavelength l of an atmosphere including aerosols is expressed as the sum: t(l)=t_gas(l)+t_aer(l),

where t_gas is the atmospheric gases optical thickness calculated using, for example, well-known spectroscopic " line-by-line " methods;

t_aer is the aerosol optical thickness calculated for an arbitrary non-homogeneous path L:

Main results presented in the publication are (see Table 2 as an example):

• Tables in the Appendix to the paper provide the computed values of the phase function for the principal aerosol models and their basic components as listed in Table 1. The calculations were made for 8 wavelengths in the UV, visible and IR regions, with an estimated relative error £ 0.3%.

• The principal optical properties of the basic aerosol components (column 2 of Table 1: soot, dust, water-soluble particles, etc...), namely - the extinction coefficient (km^-1) for a particle number concentration N=1 particle per 1 cm³; w- the single scattering albedo; g- the asymmetry factor; K_n- the normalization factor and its values at 204 angles.

• The same as above defined optical properties for non-cloudy basic aerosol models (column 1 of Table 1: continental, maritime, urban, etc...). As an example, results of the calculations for the urban aerosol model with basic components from Table 1 (water-soluble, soot, dust) are shown in Table 2.

• The optical properties for a cloudy aerosol model with a particle number concentration N₀=353.678 cm^-3 corresponding to a typical cloud water content W=0.3 g m^-3 (Ref. 7), with the modified Gamma function n(r) (Ref. 6, 7) as a particle size distribution function:

                                                                    (7)

The software package AERCOMP (FORTRAN code) allowing the determination of the optical properties of more complex aerosol models has been developed. In particular, using optical properties of basic aerosol components, one can calculate (applying linear interpolation on wavelengths and cosines of scattering angels) the optical properties for more complex, composite aerosol models. Table 2 is an example of outputs of this program.