The inverse problem was solved for the data of spectral nephelometer measurements of the directed scattering coefficients D at a scattering angle of 45°. Measurements were conducted in Moscow and Odessa regions both for ambient aerosol and its dry matter. The principle component method was applied to statistical analysis of logarithms of the retrieved size distributions of the particle cross section S(r). A correlation between statistical characteristics of lnD and lnS is considered. A relation between first eigenvectors of their covariance matrices is suggested.