Real-time monitoring of lyotropic phase evolution in ageing droplets of a surfactant atmospheric aerosol proxy: a levitation-SANS study

Aerosol particles are important components of the air we breathe. The particles we breathe in can contain compounds harmful to our health and also act as cloud condensation nuclei (CCN) to form cloud droplets, impacting the climate. The phase state of these aerosols controls the kinetics of their ageing, with more viscous particles ageing slower than less viscous particles. This results in longer atmospheric lifetimes for potentially harmful particle constituents and may slow down the creation of cloud droplets. The viscosity is therefore linked to the persistence of hygroscopic and harmful compounds bound to the particle, impacting on the climate and human health, respectively. Surfactants, such as oleic acid, are found in urban and marine aerosol emissions and we have previously shown that an oleic acid aerosol proxy can self-organise into a range of viscous lyotropic liquid crystal phases. We propose a levitation-SANS experiment to continue our successful investigations into the impact of surfactant self-organisation in atmospheric aerosol droplets. We want to systematically study how these phases evolve when exposed to simulated atmospheric ageing (oxidation by ozone and humidity cycles). After discussion with a beamline scientist, this proposal is appropriate for any TS2 SANS instrument at 4 m.