Careful inspection of the in situ TEM movies revealed water condensation and particle dissolution occurred prior to deliquescence via a multistaged dynamic process (Figure , See Supporting Movie 4 for full in situ movie). We observed three RH ranges that produced qualitatively different aerosol particle dissolution and water condensation dynamics. The RH ranges of the three stages were defined based on the water layer thickness and dynamics and the NaCl particle shape and dissolution dynamics. We note that the RH range for each condensation stage could vary from particle to particle depending on factors such as initial particle size/shape and RH inaccuracies. did not form a sessile droplet initially but instead assumed a negative curvature, wetting both the silicon nitride and the NaCl particle (Figure ). This was likely because water was found to partially wet the silicon nitride with a contact angle of 86°. It is possible the negative curvature of the region where the NaCl met the silicon nitride encouraged water condensation; however, we could not measure the 3D shape of the NaCl cube or water layer so it is not possible to estimate the local negative curvature. The intensity of the center NaCl remained the approximately same, which suggested that either water did not adhere to the top of the cube or the water layer was very thin. After deliquescence the droplet assumed a sessile droplet shape (t = 268 s). Rounding of sharp corners is consistent with prior ETEM observations and is due to the increased solubility of high curvature corners as described by the Gibbs-Thomson effect. The second stage of water condensation prior to deliquescence occurred over an RH range of about 54 -68%. Here the water layer thickness, observed as an orange halo around the NaCl in the false colored images, increased to between 100 -200 nm and the curvature of the NaCl cube corners fluctuated in time. The third stage of water condensation occurred at RH > 68% and was distinguished by a monotonic increase in the droplet area and decrease in the NaCl projected area until the aerosol particle completely dissolved. Interestingly, dissolution occurred in discrete steps instead of continuous isotropic dissolution.