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Relative humidity

Facts for Prelims (FFP)

Source: TH

Type of Humidity Definition Unit of Measurement Factors Affecting
Humidity Humidity is the amount of moisture present in the air around us.
Absolute Humidity The actual amount of water vapour present in the atmosphere grams/m³ Temperature, Location
Relative Humidity Percentage of moisture present in the atmosphere compared to its full capacity at a given temperature % Temperature, Availability of water for evaporation (Higher the RH of air, the more it is filled with moisture)
Dew Point The temperature at which saturation occurs in a given sample of air °C Temperature, Relative Humidity
Specific Humidity Weight of water vapour per unit weight of air g/kg


Why does relative humidity matter?


Relative humidity plays a significant role in how comfortable we feel in different environments. When the relative humidity is high, the air is already filled with moisture, and the sweat on our skin can’t evaporate. This makes it difficult for our bodies to cool down, which can be dangerous in hot weather. In general, a relative humidity of 30-60% is considered comfortable, and environments with lower humidity may require humidifiers to increase moisture levels. On the other hand, a fan can be useful in areas with higher humidity to help move the air and promote sweat evaporation.


What is Wet Bulb Temperature?

Wet bulb temperature is the lowest temperature to which air can be cooled by the evaporation of water at constant pressure, and it is a limit beyond which humans cannot tolerate high temperatures. It is measured by wrapping a wet cloth on a thermometer to observe the temperature at which evaporation occurs. The highest acceptable wet-bulb temperature for humans is 35°C (95°F) for six hours, above which serious health problems can develop, even for healthy individuals.