saturation vapour pressure

Saturation vapor pressure refers to the maximum pressure exerted by a vapor when it is in equilibrium with its liquid state at a specific temperature. In atmospheric science, this concept is crucial for understanding humidity.1

The saturation deficit is an index of humidity calculated as the difference between the saturation vapor pressure and the actual vapor pressure of a volume of air. This deficit is directly proportional to the air's evaporation capability. As temperature increases, so does the saturation vapor pressure. Consequently, even with the same relative humidity, warmer temperatures lead to a greater saturation deficit and increased evaporation. For example, at 25°C, if air has a vapor pressure of 17 millibars (mb) and the saturation vapor pressure is 31 mb, the saturation deficit is 14 mb.23