The mechanisms of gravito-photophoresis for aerosol aggregates in the free-molecular regime

Summary form only given. The gravito-photophoretic forces in the free-molecular regime are calculated for the some types of aerosol particles by using the Monte-Carlo method to estimate molecular transfer. The absorption cross sections of aggregate components are calculated according to the results of the light scattering theory for fractal systems obtained within the framework of Berry-Percival´s method and in the work by S. D. Andreev. It is shown that two types of gravito-photophoresis can contribute to the levitation of aerosol particles absorbing the Sun and the Earth´s radiation. There is a well-known /spl Delta//spl alpha/-gravito-photophoresis caused by a difference in the thermal accommodation coefficient, and there is a /spl Delta/T-gravito-photophoresis, when the aerosol aggregate consists of individual particles differing in temperature due to a difference in the physical properties and the radiation absorption power. Both mechanisms can induce large-value lifting forces able to provide a vertical transport of aerosol particles into the upper atmosphere. A connection between the existence of aerosol layers at the altitudes near 20, 50, 70-100 km in the real Earth´s atmosphere, according to the results of our space observations in the ultraviolet range, and a condition of the balance of photophoretic and gravity forces is shown.