REBECCA CRAIG, Andrew Ault, University of Michigan
Abstract Number: 515 Working Group: Aerosol Chemistry
Abstract Secondary organic aerosol (SOA) formation and many of the subsequent multiphase chemical and physical processes SOA particles undergo are highly dependent on acidity. One such physical process is liquid-liquid phase separation (LLPS), which occurs commonly in atmospheric SOA particles. Relative humidity (RH), particle size, and chemical composition effects on LLPS have been characterized in laboratory studies, but few have focused on pH impacts on LLPS. Previous work has found that increasing pH corresponds to a decrease in the separation RH and that once LLPS occurs, the organic-rich phase is less acidic than the previously single phase particle. However, these studies have investigated primarily large particles (20-200 μm) at pH levels higher than what thermodynamic models predict for atmospheric aerosols. Herein, we investigate LLPS of laboratory-generated SOA particles composed of ammonium sulfate and polyethylene glycol 400 at atmospherically relevant sizes and pH’s. Both bulk aerosol and individual particle pH are measured via established pH indicator paper and spectroscopic methods, respectively. The results of this study could have implications for acidity-dependent particle phase processes and how aerosol particle composition and morphology influence climate effects.