A wet-bulb temperature is the lowest temperature that can be reached by evaporation of water only. At this temperature, the water absorption capacity of a gas (air) is in equilibrium with the water release capacity of a wet surface, which also includes liquid droplets in a gas atmosphere.

The wet-bulb temperature is a key factor in the design of gas scrubbers such as jet scrubbers and columns because it has a major impact on the gas outlet volumetric flow rate. Wet-bulb temperatures in gas scrubbers like jet scrubbers and columns usually range between 40 and 70°C, even at gas inlet temperatures of several hundred degrees Celsius. When >100°C gases are called down, this is also called quenching.