Influence of slightly soluble organics on aerosol activation

Abstract

This paper examines the effects of slightly soluble organics on aerosol activation in a parcel of air rising adiabatically. Slightly soluble organics can affect aerosol activation by three mechanisms: lowering surface tension, altering the bulk hygroscopicity, and delaying the growth of particles because of their lower solubilities. The first and second mechanisms have already been addressed in a previous paper. Here we address the third mechanism by simulating the activation process of aerosol particles modeled using a single lognormal size distribution and consisting of an internal uniform chemical mixture of adipic acid (representing slightly soluble organics having extremely low solubility as a worst‐case scenario) and ammonium sulfate. The simulations were carried out using measured solubility of adipic acid spanning a wide range of physical and dynamical parameters. The same conditions were resimulated but assuming fully soluble aerosols. Results of the simulations show that although the low solubility of the adipic acid alters Köhler curves and increases critical supersaturation of the smaller particles (Köhler curves of the larger particles are not affected because these particles are completely dissolved at the initial supersaturation of zero), low solubility has minimal to no effect on the parcel supersaturation except for particles consisting of more than 95% adipic acid. Furthermore, since aerosols in realistic atmospheric conditions do not contain more than 90% organics, we should be only interested in smaller concentrations (less than 90% by mass). Accordingly, we conclude that the slightly soluble organics can be assumed to be fully soluble for the purpose of predicting the fraction of activation and the maximum supersaturation with negligible error and it is not necessary to retune the previously developed parameterization of aerosol activation.