Kinetic processes in the condensation and evaporation of aerosols

Abstract

The stable and metastable states of a vapour are considered in relation to the process of condensation. By modelling these states on a gaseous system of growing and evaporating molecular clusters, kinetically balanced, and by consideration of the requirements of the thermodynamic limit, two important properties may be defined; a number J, dependent on temperature and pressure, which is a parameter of the cluster populations, and an interfacial free energy ζ, which varies with temperature and cluster size but not with pressure. Expressions for J and ζ, and for the critical cluster size in metastable states, are derived for simple models of cluster reactions. The rates of these reactions are considered for particles in the form of large clusters, and coefficients of evaporation and growth obtained which tend to zero with increase in particle size. It is concluded that particles of visible size are not formed by spontaneous condensation under uniform conditions of temperature and pressure.