Theoretical grounds of the Kasten formula

摘要

The experimental data provide support for the conclusion that the atmosphere and aerosol particle form a linear dynamic system. The behavior of aerosol particle in the coordinates: the logarithm of undersaturation coefficient of water vapor and the logarithm of the relation of the equilibrium particle size to the dehydrated particle size is given by the straight line segments. Each segment is characterized by its coefficient of condensation activity. Aerosol particle of chemically pure substances and sometimes the atmospheric aerosol particles are denoted in this plot by a straight line corresponding to the condensation activity coefficient, being equal to infinity. Now we denote the relative humidity corresponding to this segment as a specific point. The precipitation of water molecules on aerosol particle ,is due to a tendency of the surface to decrease its energy, i.e., to decrease the surface tension. With increasing the relative humidity from zero to the specific point the adsorption takes place, i.e., water molecules cover the particle surface with a monolayer. At the specific point the interphase surface tension of the particle-monolayer system becomes equal to zero, i.e., absorption begins. If in the atmosphere the relative humidity is supported, which is slightly less than the value of the specific point, during a long period of time, then the heat energy of atmospheric molecules is large enough for splitting a particle to small parts and for changing significantly the particle size distribution over a long period of time. In this case the reversible process of coagulation is very slow because the energy gain is low at the particle coalescence.