Secondary organic aerosols (SOA) with diverse chemical compositions can act as cloud condensation nuclei (CCN), affecting cloud formation and properties, and thus climate change. At different relative humidity (RH), these fine solid particles or droplets in the atmosphere can be liquid to semi-solid in their phase, affecting their propensity to absorb water. Our lab investigates patterns in water diffusivity with variations in equilibrium mass fraction of water (MFW) by using saccharide-water films as simple models for water-soluble SOA. ATR-FTIR is used to measure the bond vibrations in the bottom layer of the film to determine the equilibrium water content. Films with different components will have diverse equilibrium MFW, thus leading to differences in the water absorption behaviors. To increase the complexity of saccharide films, we mix sucrose and other molecules such as glucose, glycerol, trehalose, and citric acid to compare the water uptake rates with pure sucrose film. We apply the AIOMFAC (Aerosol Inorganic-Organic Mixture Functional Group Activity Coefficient) model to our mixture system to compare model values with our experimental equilibrium MFW. Preliminary results indicate trehalose-sucrose mixtures’ MFW may deviate from AIOMFAC model values, and the origin of this difference will be confirmed with future experiments.

Exploring equilibrium water content in binary mixtures as atmospheric aerosol models

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