Results are presented of aerosol extinction coefficient measurement in air layers over ground and water a (L) at at wavelength L a belongs to (380. 1100 nm) made by means of the multi-channel transmission meters at Belsk Geophysical Observation (BCO) and in Gdynia, Poland, as well as the results of vertical aerosol optical thickness measurements .r (L).at La belongs.(380, 667 nm)made by means of Linke's radiometer at BGO and aerosol back-scattering coefficients profiles in the stratosphere: B (L=532 nm) made at BGO and Institute of Physics in Minsk (Byelorussia) by means of lidar. On the basis of these measurements, are we determined by using randomized minimization search technique (RMST) and bimodal log-normal model of the aerosol, the following parameters: particle number density concentration N, particle volume concentration V, mean model radius amm and effective particle radius a of the atmospheric aerosols. It was found the during the last few years (199201998) 'cleaning of the atmosphere over Poland took place and the transformation of aerosol towards the smaller particles (there was observed a decrease of V- proportional to the weight concentration, a decrease of a and along with an increase of N.)