Up to this point, we have assumed that the evaporating droplets remain liquid throughout the RH range, even down to full dry conditions at 0% RH in the limit of zero water content. The solubility limit of sodium chloride is surpassed as the RH decreases below 75%; in aerosol droplets, the crystallisation relative humidity is 45% RH, corresponding to a supersaturation of ~2, i.e. a solute concentration that is a factor of 2 higher than can be supported in a bulk solution. Such high salt concentrations are expected to play a role in the loss of viability of bacteria and the infectivity of viruses. The phase behaviour of saliva and deep lung fluid droplets remains uncertain, despite their high salt contents.