where 𝑐 𝑁𝑎𝐶𝑙 is the curvature dependent solubility, 𝑐 ∞ is the bulk solubility, 𝜎 is the surface energy of the NaCl, 𝑉 𝑚 is the molar volume of solid NaCl. Interestingly, there was minimal change to the projected area of the NaCl particle or water droplet while the RH increased by ~10%. This suggests that the water droplet was saturated with NaCl over this range, halting dissolution. We propose that fluctuations in the NaCl nanoparticle shape were due to small scale fluctuations in local water partial pressure or vapor pressure at the droplet surface, which caused water exchange between the droplet and vapor phase. A second potential pathway for the corner curvature fluctuations is surface diffusion of NaCl from regions of high curvature to low curvature (Figure .iii). High curvature cube corners have intrinsically higher chemical potential compared to regions of lower curvature. Instead of dissolving into solution, NaCl ion pairs at high curvature regions could respond to local decreases in droplet solute concentration by moving to regions of lower curvature and chemical potential via surface diffusion. Deposition of NaCl on the cube faces separating adjacent corners was not observed because the <100> facets are stable and defect free, which introduces a substantial nucleation energy barrier. Instead, NaCl ion pairs moved along the <100> facets, potentially as rapidly diffusing "floating islands," and deposited on cube corners that contain defects and low coordination number surface sites with low nucleation energy barriers. This proposed mechanism is consistent with the experimentally observed anti-correlation between the curvature of adjacent corners and the uncorrelated curvature changes of non-adjacent cube corners (Figure ).