MODIFICATION OF THE KUHLER EQUATION TO INCLUDE SOLUBLE TRACE GASES AND SLIGHTLY SOLUBLE SUBSTANCES

A generalized reformulation of the Kohler theory to include the effect of soluble gases and slightly soluble aerosol substances is presented . A single equation is derived that takes into account 1) the Kelvin e ffect; 2) the Raoult effect caused by highly soluble aerosol material (salt); 3) increase in droplet radius due to an undissolved, insoluble , or slightly soluble core; 4) contribution of solute into the droplet by a slightly soluble substance; and 5) contribution of hygroscopic m aterial into the droplet by a soluble trace gas allowed to deplete fro m the gas phase because of the condensational growth of the droplets ( assuming a monodisperse size distribution). Model calculations are pre sented for a system in which the aerosol is composed of a slightly sol uble CaSO4 core coated with ammonium sulfate, and the gas phase contai ns HNO3. It is shown that the resulting equilibrium curves allow the o ccurrence of stable, unactivated droplets with radii up to about 10 mu m at realistic ambient conditions. The equilibrium curves show in som e cases-local minima and maxima, the reasons for and consequences of w hich are discussed. The results of this study suggest that a new defin ition for ''activated droplet'' is needed.