The internal arrangement of components within an atmospheric aerosol particle impacts its radiative properties, activity towards cloud droplet formation, and heterogeneous chemistry.  Characterizing particle morphology poses challenges due to the prevalence of submicron aerosol particles in the atmosphere.  This talk details our single particle measurements of laboratory-generated submicron aerosol particles that undergo liquid-liquid phase separation, using cryogenic-transmission electron microscopy as our primary technique.  We have found that liquid-liquid phase separation exhibits a size dependence, where sufficiently small particles cannot overcome the activation barrier needed to form a second liquid phase.  Through studies of drying rate, we find that the size dependence has both thermodynamic and kinetic contributions.  This size dependence is found in both simple and complex model systems consisting of one or more organic compounds mixed with ammonium sulfate, as well as mixtures of aqueous polymers.  We have also investigated the role of the identity of the salt on the size dependence, finding that cations control the transition between where particles are phase separated vs. well-mixed.  Recently, we have explored the dynamics of the phase separation process and are engaged in determining experimental phase diagrams for submicron particles.  These studies provide detailed insights into particle morphology, which will ultimately aid the atmospheric community in modeling the effects of particle morphology on atmospheric processes.

Liquid-liquid phase separation in submicron aerosol particles

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