Aerosol particles can exist as solution droplets, viscous semi-solids, glasses or crystalline solids. Responding to changes in the surrounding gas phase environment, particles can grow by water condensation changing rapidly in composition and, possibly, changing dramatically in viscosity. The timescale for condensational growth is important to establish for particles undergoing processes in the atmosphere or during inhalation. Here, we report direct measurements of the timescales for condensational growth on a range of model aerosol systems extending from viscous aerosol particles containing a single saccharide solute (sucrose, glucose, raffinose or trehalose) and a starting viscosity equivalent to a glass of ~1012 Pa s, through to non-viscous sodium nitrate or tetraethylene glycol particles. Measurements are reported at -7.5, 0 and 20 oC using an electrodynamic balance for particles of initial size ~8-10 m. Overall, the condensation timescales observed in this work indicate that water condensation occurs rapidly at all temperatures examined (< 10 s) and for particles of all initial viscosities spanning 10-2 to 1012 Pa·s, with only a marginal delay (<1 order of magnitude) for particles starting as a glass. This conclusion is significant for both cloud formation processes (droplets < 1 μm should track changes in gas phase RH) and inhalation formulations (droplets > 1 μm may require longer timescales for equilibration than inhalation).
|Date made available||31 May 2018|
|Publisher||University of Bristol|