Water nucleation on aerosol particles containing both organic and soluble inorganic substances

A theory of the formation of water droplets on aerosol particles consisting of soluble inorganic salts and organic (soluble, insoluble and surface active) substances has been developed. The case of partially wettable spherical insoluble core is considered. The theory links the interfacial free energies of the surfaces, the size of the insoluble core, and the chemical characteristics of the soluble substances with the ability of the aerosols to form water droplets. The theory is compared with Kohler theory and major differences in the equilibrium pressure of water vapour and nucleation rate were found. The influence of various types of organic material on CCN activation is considered. It is shown that the presence of both soluble and insoluble organic substances in CCN can affect their ability to form cloud droplets. Surface active substances are found to be the most important components of organic matter that are able to considerably affect CCN activation. A CCN containing ammonium sulphate, sodium chloride or another salt and surface active agent is activated under lower supersaturation than CCN containing only salts. The presence of surface agents in CCN could lead to greater concentration of cloud droplets. Thus, varying the concentration of surface active substances in atmospheric aerosols may alter the number concentration of cloud droplets and the radiative properties of clouds. (C) 1998 Elsevier Science B.V. All rights reserved.