Organic aerosol acts as cloud condensation nuclei (CCN) to influence cloud formation and properties, thus affecting climate change. How the water diffusion constant changes with water content can be investigated by using sucrose layers as a simple model of water-soluble secondary organic aerosol (SOA). ATR-FTIR was used to measure bond vibrations and find how the water and saccharide content changes in the bottom layer of the film. A high refractive index germanium crystal in a flow cell in the ATR holder allows air to flow at different relative humidities over the layers. Sucrose-water systems' viscosity changes with relative humidity and the viscosities of the films range from very viscous glasses to watery solutions. Stable highly viscous films are necessary for reproducible water uptake studies. To increase the film complexity of these stable films, we focus on making different saccharides films with a similar mass fraction of solute (MFS) by mixing sucrose and other molecules to compare the water uptake for pure sucrose versus mixed saccharide films. We expect the simpler, smaller size and lower molecular weight molecules such as glucose and hexanetriol will show a faster water transport than pure sucrose film while larger molecules such as polyethylene glycol oligomers will slow water uptake.

Tracking water uptake in saccharide thin film atmospheric aerosol models using FTIR-ATR spectroscopy

ACS Spring 2022

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