A gas-disperse mixture sampled from the near-ground atmosphere into a closed volume (1800 m3) of the Big Aerosol Chamber (BAC) was subjected to long irradiation by an ultraviolet lamp (DRT-1000). As a result of irradiation, the increased concentration of ozone was formed in BAC and the fine fraction of aerosol particles with the size r < 80 nm was intensely generated. In the course of the experiment, a spectronephelometer measured current values of the polarization components of the directed scattering coefficient β⊥,||(λi, θj). The time series of β⊥,||(λi, θj, tk) measured by the polarization nephelometer at four wavelengths λi = 455, 525, 585, 630 nm and five scattering angles θ j= 15, 45, 110, 135, 165° were used for numerical solution of the inverse problem of aerosol scattering. The evolution of the size spectrum of aerosol particles in the fine fraction with r < 200 nm has been traced.