# When does water vapor in air condense?

Mar 12, 2016

Depends on the availability of condensation nuclei, but generally at the dew point.

#### Explanation:

First of you need to understand that water molecules can be at different energy levels at many temperature. Therefore at any given temperature you can have water molecules of different states. This is because energy is not always distributed evenly between particles. At 0 degrees, the average temperature of the particles is 0 but individual molecules can have more or less energy.

At a given temperature there is a maximum amount of water vapor the air can hold.

The red line equals the maximum amount of grams of water a kilogram of air can hold at a given temperature. So if you are adding water to air then once the number of grams per kilogram is reached, any additional water vapor will condense automatically. Conversely, if you have a constant amount of water in the air and you cool it, eventually it will reach a temperature where the amount of water is the maximum. At this point condensation occurs.

The temperature where the air is holding all the water it can is called the dew point.