Humidification
Introduction
[1] Atmospheric humidity is due to the water vapor that is present in the atmosphere. Vapor comes from the evaporation of terrestrial water masses and, to a lesser extent, from evapotranspiration from soils and plants. The amount of water vapor that air can absorb depends on its temperature. Hot air admits more water vapor than cold air.
One way to measure atmospheric humidity is with a hygrometer.
Water vapor has a lower density than air; Therefore, humid air (a mixture of air and water vapor) is less dense than dry air. On the other hand, substances expand when heated, which gives them lower density. All of this causes hot air containing water vapor to rise in the Earth's atmosphere. The temperature of the atmosphere decreases an average of 0.6 °C every 100 m in wet adiabatic, and 1.0 °C, in dry adiabatic. Upon reaching colder areas, water vapor condenses and forms clouds (water droplets or ice crystals). When these water droplets or ice crystals weigh too much, they fall and cause precipitation "Precipitation (meteorology)") in the form of rain or snow.
Evaluation of air humidity in the environment
Composition of dry air
Dry air, at sea level, has the following composition by weight:
Specific volume of dry air
Dry air with a temperature relatively close to its critical temperature can be considered a perfect gas, in which:.
Specific volume of water vapor
For the same reason indicated for air, since its pressure is low in relation to its critical pressure, it can be considered a perfect gas; therefore:.
Dalton's Law
According to the Law of partial pressures (Dalton's law), the total pressure of a mixture of several gases is equal to the sum of the partial pressures that each of the components would exert if, at the same temperature, they alone occupied the same volume as the mixture.