The many-year trend of aerosol number density, earlier revealed by the authors, was shown to be mainly due to variations of the particle submicron fraction. The particle number density of the coarse-dispersed fraction varies randomly near some mean value. As a result, the total amount of the aerosol matter in the atmosphere varies within much more narrow limits than the number density. Analysis of the ion and element composition of aerosol has shown that the aerosol number density decreases due to compounds of natural origin.