Flat versus Curved Water Surfaces

• given flat and curved water surfaces where the air adjacent to each is saturated -->>
• more energy is required to maintain the "curvature" of the drop
• therefore, the water molecules on the surface of the drop have more energy
• therefore, they evaporate more readily that from the flat water surface (compare the length of the red arrows)
• therefore: evaporation rate off curved surface > evaporation rate off of flat surface
• since air above both surfaces is saturated, then
• evaporation rate = condensation rate
• therefore, condensation rate onto droplet > condensation rate onto flat water surface
• therefore, e_sdrop > e_sflat
• therefore:
  • if RH_flat = 100%, then RH_drop > 100%
  • the air surrounding the drop must be supersaturated!!
• This is called the curvature effect