What is the concept of relative humidity 100%?

Under different conditions, the amount of water dissolved (or evaporated) in the air is limited. For example, 30 degrees is 1 m3 air can dissolve 30.38 grams of water. When 30.38g of water is dissolved in 1 m3 of completely dry air, the humidity is 100.

Relative humidity is the percentage of actual water vapor content (absolute humidity) and saturated humidity (maximum possible water vapor content) at the same temperature. It is only a relative number and does not represent the absolute humidity in the air.

100% is the maximum value. If the water vapor in the air exceeds saturation, it should condense into water droplets.

At a certain temperature, a certain volume of air can only hold a certain amount of water vapor. If the amount of water vapor reaches the limit that the air can hold water vapor, the air will reach saturation, and the relative humidity is 100%. In a saturated state, water will not evaporate.

In this kind of weather in hot summer, the sweat secreted by the human body is difficult to evaporate, and it is sultry. On the contrary, in autumn, people sometimes encounter the "autumn tiger" with high temperature, but because the humidity is obviously reduced, people seldom feel "sultry". If you encounter low temperature and high humidity in winter, people will feel wet and cold. The humidity in the air is too small, which will also make people feel uncomfortable.

Relative humidity refers to the percentage of water vapor pressure in the air to saturated water vapor pressure at the same temperature. Or the ratio of the absolute humidity of wet air to the maximum absolute humidity that can be achieved at the same temperature. It can also be expressed as the ratio of the partial pressure of water vapor in wet air to the saturated pressure of water at the same temperature.

References:

Relative humidity of Baidu encyclopedia entries