What is Relative Humidity?

Relative humidity refers to the percentage of the water vapor pressure in the air to the 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 reached at the same temperature. It can also be expressed as the ratio of the partial pressure of water vapor in wet air to the saturation pressure of water at the same temperature.

Relative Humidity (RH). The ratio of the absolute humidity in the air to the saturated absolute humidity at the same temperature and pressure. The number is a percentage. (That is to say, the ratio of the mass of water vapor in a humid air to the mass of water vapor in saturated air at the same temperature and pressure. , Which means relative humidity.)

The most primitive hygrometer is like the old-fashioned medical type

Relative humidity is the percentage of water vapor density (represented by d1) and saturated water vapor density (represented by d2) at the same temperature in a unit volume of air, that is, RH (%) = d1 / d2 x 100%; another This calculation method is: the actual air water pressure (represented by p1) and the percentage of saturated water pressure (represented by p2) at the same temperature, that is, RH (%) = p1 / p2 x 100%.

Formula for calculating relative humidity using dry and wet bulb temperature

1 Calculation formula of relative humidity U:

Where U is the relative humidity, E is the water pressure (hPa), and Ew is the pure horizontal liquid (or ice) saturated water pressure (hPa) corresponding to the dry bulb temperature t (° C).

2 Calculation formula of water pressure E

Where Etw (hPa) is the saturated water pressure of the pure horizontal liquid surface corresponding to the wet bulb temperature tw (° C). When the wet bulb freezes and the wet bulb temperature is lower than 0 ° C, it is the saturated water pressure of the pure horizontal ice surface; A is the coefficient of wet and dry table. The coefficient of ventilation when the wet ball is not frozen (ventilation speed 2.5m / s) is 0.662 × 10-3 -1. Speed 2.5m / s) The coefficient is 0.584 × 10-3 -1; Ph is the pressure of the station (hPa); other symbols have the same meaning as above.

3 Calculation formula of saturated water pressure Ew:

3.1 Calculation formula for saturated horizontal water pressure

Where Tl = 273.16 (absolute temperature of the triple point of water, unit: K) T = 273.15+ (absolute temperature, unit: K).

3.2 Calculation formula for saturated horizontal water pressure on pure ice

The meaning of the symbols in the formula is the same as above.

Impact on human health

Every winter, the climate is extremely dry. Maintaining relative humidity in the room prevents colds. According to measurements, only 2.5 of the 120 heating days in the northern region reached healthy humidity, and other studies have shown that

Water vapor is the most important energy carrier in the atmosphere and the most important greenhouse gas. Therefore, its spatiotemporal distribution has a considerable impact on weather and climate through latent heat exchange, radiative cooling and heating, cloud formation and rainfall, and thus affects the growth environment of animals and plants. The change is the main driving force for vegetation change. Agricultural production has a certain impact. Therefore, the research on humidity has become more and more important. In addition, relative humidity also has a great impact on industrial processes. It also has a systematic effect on the rate of solar warming by affecting the optical characteristics of aerosols, which is of significance to the climate effect of aerosols; of course, relative humidity has Visibility also has a certain effect. Therefore, studying the trend of large relative humidity changes in the context of global change is of great practical significance for understanding environmental changes and adjusting production. ^[3]