Saturation Vapor Pressure

Saturation vapor pressure is the equilibrium partial pressure of water vapor over a flat liquid surface at a given temperature, the pressure at which evaporation and condensation balance. It depends almost only on temperature, rising steeply per the Clausius-Clapeyron relation at roughly 7 percent per kelvin, from about 6.1 hPa at 0 C to 23.4 hPa at 20 C. Over seawater it is reduced about 2 percent by dissolved salts. The difference between saturation vapor pressure at the sea surface and the actual vapor pressure of the air drives evaporation and the latent heat flux, the dominant term cooling the tropical ocean.