Editing Humidity (section)

=== Enhancement factor ===
The enhancement factor <math> (f_w) </math> is defined as the ratio of the saturated vapor pressure of water in moist air <math> (e'_w) </math> to the saturated vapor pressure of pure water:
<math display="block"> f_W = \frac{e'_w}{e^*_w}. </math>

The enhancement factor is equal to unity for ideal gas systems. However, in real systems the interaction effects between gas molecules result in a small increase of the equilibrium vapor pressure of water in air relative to equilibrium vapor pressure of pure water vapor. Therefore, the enhancement factor is normally slightly greater than unity for real systems.

The enhancement factor is commonly used to correct the equilibrium vapor pressure of water vapor when empirical relationships, such as those developed by Wexler, Goff, and Gratch, are used to estimate the properties of psychrometric systems.

Buck has reported that, at sea level, the vapor pressure of water in saturated moist air amounts to an increase of approximately 0.5% over the equilibrium vapor pressure of pure water.{{sfn|Buck|1981|pp=1527–1532}}