Size evolution of a soluble aerosol particle in air

Abstract

The mechanisms responsible for hygroscopic growth/reduction in the size of water-soluble aerosol particles have a significant effect on the dynamics of coagulation and sedimentation processes in aerosol systems. By now, there is a large amount of experimental and theoretical works devoted to the study of hygroscopic growth and decrease in the size of particles of various chemical nature. Along with complex multilayer models of aerosol particle growth, the models based on a modification of the Maxwell equation for condensation and evaporation of droplets are commonly used. They allow taking into account temperature effects, the influence of the surface curvature of the particle and the presence of soluble substances in it. This paper proposes a mathematical model of the size evolution of water-soluble aerosol particles that, together with the listed effects, takes into account the change in the size of the undissolved particle core. This makes it possible to simulate all the stages of hygroscopic change in particle size, starting from the transformation of a crystal core into a drop to its subsequent growth, and also back, from the evaporation of a drop to the formation of a crystal. Using the proposed model, various scenarios of changing the state of the particle are modeled for different combinations of the initial states of the particle and the relative humidity of the air. It is shown that the predictions from the model are qualitatively and quantitatively consistent with the experimental data on the size evolution of sodium chloride particles in humidification and drying processes, as well as with the results of measurements of particle sizes in equilibrium states with increasing and decreasing relative humidity. The developed model can be used to solve different fundamental and applied problems of the dynamics of water-soluble aerosol systems.