A general detailed formulation of the problem of calculating the equilibrium concentration of primary cosmic dust particles at altitudes from 30 to 110 m is presented. The flux of micrometeorites in the mass range from 10–17 to 10–8g is preset at zmax = 110 km while the source of vapors of the micrometeoric matter is assumed to obey the Gaussian vertical distribution with the maximum at z0 = 95 km and with a standard deviation of ± 5 km . The sink for this cosmic dust aerosol is the Junge layer of the sulphate aerosol at z min = 20 km . The micrometeoric matter influx is assumed to be 45 tons per day.
As numerical calculations have shown, the condensation of vapors of the meteoric matter takes place at the altitudes of from 18 to 100·km. Below 50 km the coagulation process leads to the quick formation of aerosol particles. Thus formed aerosol particles with masses m = 10 g scatter light most effectively. As a result, the atmospheric turbidity increases with z decreasing. Further increase of the aerosol particle size leads to the increase of the sedimentation rate and, as a consequence, the atmospheric turbidity at altitudes below 30 km decreases. This model is the first one which gives the mechanism for the formation of the upper stratospheric light scattering layer of aerosol observed during dusk (see Refs. 8 , 11 , 13 , 14 , and 21).