  A quantitative understanding of the evaporative drying kinetics and
nucleation rates of aqueous based aerosol droplets is important for a wide
range of applications, from atmospheric aerosols to industrial processes such
as spray drying. Here, we introduce a numerical model for interpreting
measurements of the evaporation rate and phase change of drying free droplets
made using a single particle approach. We explore the evaporation of aqueous
sodium chloride and sodium nitrate solution droplets. Although the chloride
salt is observed to reproducibly crystallise at all drying rates, the nitrate
salt solution can lose virtually all of its water content without
crystallising. The latter phenomenon has implications for our understanding of
the competition between the drying rate and nucleation kinetics in these two
systems. The nucleation model is used in combination with the measurements of
crystallisation events to infer nucleation rates at varying equilibrium state
points, showing that classical nucleation theory provides a good description of
the crystallisation of the chloride salt but not the nitrate salt solution
droplets. The reasons for this difference are considered.
