What is the relationship between air humidity and it?

The degree of air humidity can be expressed by professional physical quantity air humidity.

The air humidity is related to the water content in the air, and the temperature directly affects the water content in the air.

At a certain temperature, the less water vapor in a certain volume of air, the drier the air; The more water vapor, the wetter the air. In this sense, it is often expressed by physical quantities such as absolute humidity, relative humidity, relative humidity, mixing ratio, saturation deficit and dew point. If the weight of liquid water in wet steam accounts for the percentage of the total weight of steam, it is called the humidity of steam.

The higher the temperature of air, the higher its ability to contain water vapor (different from water vapor). Although water vapor can react with some components in the air (such as salt in suspended dust) or be absorbed by porous particles, these processes or reactions account for a small proportion. On the contrary, most water vapor can be dissolved in the air. Dry air can generally be regarded as an ideal gas, but with the increase of water vapor composition, its ideality is getting lower and lower. At this time, only van der Waals equation can describe its performance.

Theoretically, the statement that "the water vapor in the air is saturated" is incorrect, because the water vapor saturation in the air has nothing to do with the composition of the air itself, but only with the temperature of the water vapor. At the same temperature, the saturation of water vapor in vacuum is actually as high as that in air. But for the sake of simplicity, people (even in the scientific community) use the words "dissolved water vapor in the air" or "saturated water vapor in the air".