We analyze the optical characteristics and microstructure parameters of the submicron aerosol retrieved from spectronephelometric measurement data acquired during smog episode in Beijing occurred in November 2003. It was shown that the increase of the aerosol volume concentration during smog formation is caused mainly by the growth of particle size rather than number concentration. In the process of aerosol accumulation in the ground layer, its parameters undergo matched variations. Thus, the effective radius increases, while the width of the size spectra, particle refractive index, and relative soot content decrease.