Mechanism of Phase Separation in Organic Aerosol

Abstract:

The morphology of aerosol particles impacts their formation, reactivity, and interactions with light and clouds. We have investigated phase separation in aerosol particles composed organic compounds and ammonium sulfate using optical microscopy and cryogenic transmission electron microscopy. Phase separation can occur as water is evaporated from particles due to salting out of the organic component by ammonium sulfate. In previous studies, we have observed that certain submicron particles have a size-dependent morphology in which large particles are phase separated and small particles (less than approximately 200 nm) are homogeneous. In this talk, we will probe the origins of the size dependent behavior and the phase separation process. In particular, we have investigated model phase separating systems to explore the origins of the size dependence. To determine the mechanism of phase separation of organic compounds with ammonium sulfate, we have investigated the phase separation behavior of numerous compounds of different molecular architectures with the same O:C ratio. We will comment on the impact of our results on understanding salting out of organic compounds and the size dependence of particle morphology.