The Dew Point, absolute humidity and relative humidity

Some of the science behind drying

What is the DEW POINT of air?

The DEW POINT of air is expressed as a temperature (degrees Celsius).
When air cools down to this temperature (the DEW POINT), the water vapour contained by the air starts to condense, which is visible in the form of dew, fog, mist or condensation on smooth, cold surfaces.

Very dry climate

Very humid climate

The dew point can never be higher than the actual air temperature.
If the actual air temperature drops to the dew point, the air will become saturated with water in the form of dew, fog or condensation.

The closer the dew point is to the actual air temperature, the more humid the air is.

Two extreme examples:

In very humid areas, the dew point is very close to, but just below, the actual air temperature, for instance, in and near tropical rainforests, or near oceans.
In very dry areas, the dew point is very far from, and much lower than, the actual air temperature, like, for instance, in the Thar Desert in India, or the Gobi desert in China.

What is absolute humidity?

If a certain amount of air, let's say 1 kg, contains a certain amount of water, let's say 16.1 gr., then we can state that the Absolute Humidity is 16.1 gr of Water per Kg of Air. Absolute Humidity cannot be measured, only calculated, and is expressed in grams of water per kg of air.

What is relative humidity?

The ratio of the amount of moisture in the air at a specific temperature to the maximum amount (100%) of water that the air could hold at that specific temperature, expressed in a percentage. Relative humidity can be measured.