Humidity

Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present.

Types of Humidity

There are three main measurements of humidity: absolute, relative and specific.

• Absolute humidity describes the water content of air and is expressed in either grams per cubic meter or grams per kilogram.
• Relative humidity, expressed as a percent, measures the current absolute humidity relative to the maximum for that temperature.
• Specific humidity is a ratio of the water vapor content of the mixture to the total air content on a mass basis.

Effects on Humans

The human body dissipates heat through perspiration and its evaporation. Heat dissipation is inhibited by high humidity because the rate of evaporation of moisture from the skin decreases with increasing humidity even if the ambient temperature itself is relatively low.

Measurement

Humidity is measured by means of a hygrometer. The measurements are usually expressed as specific humidity or relative humidity.

See Also

• Dew point
• Psychrometrics
• Hygrometer

References

Humidity Resources
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