Few-parameter descriptions of distribution of the near-horizon brightness fields are presented, which are based on model calculations for aerosol-gaseous spherical atmosphere. The results of numerical simulation are compared with experimental data. A new method of determination of the aerosol optical depth (AOD) from measurements of near-horizon sky brightness is suggested. The advantage of this method is that it does not require the absolute calibration of instruments: AOD is retrieved from relative measurements of the angular position of the sky brightness maximum.