Explain why very small cloud droplets of pure water evaporate even when the relative humidity is 100 percent.

Very small cloud droplets of pure water evaporate even when the relative humidity is 100 percent because of the curvature of the droplets surface.

Explanation:

The curvature of a droplet's surface, the molecules present over the surface are much exposed to their surrounding, perhaps less tightly bound by the surface tension force and hence evaporate more speedily than molecules present over the plane surface. For which the saturation vapor pressure of the surface goes up slightly with the curvature of that surface and also with relative humidity. By which the surface is in the equilibrium to more than 100 percent.