The state of water plays an important role in earth's radiation balance, energy balance, and thus climate. Evaporation is the transformation of water from liquid to vapor state. This transformation requires energy and is a cooling process. The net evaporation is the net transfer of water molecules from liquid to vapor. Liquid to vapor transfer by plants is called transpiration .
Condensation is the transformation of water from a vapor to a liquid state.
In the atmosphere CN include salt particles and dust particles. Condensation occurs primarily when air is cooled. Saturation of air occurs when the number of water molecules entering a volume is equal to the number leaving the volume. In reference to a water surface and air, the net exchange of molecules is equal at saturation. Moisture Variables Humidity refers to the amount or concentration of water vapor in the air.