Absolute Humidity, Specific Humidity & Relative Humidity YouTube Lecture Handouts

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  • Humidity is the amount of moisture (water vapor) in the air.

  • Saturation: When gas holds maximum water vapor at a given temperature (holding capacity increases with rising temperature)

Absolute Humidity

  • Mass of water vapor divided by a unit volume of air (grams of water/cm3 of air)

  • It does not take temperature into consideration

  • Absolute humidity in the atmosphere ranges from near zero to roughly 30 gm/m3 when the air is saturated at 30 °C

Relative Humidity

  • Ratio of the partial pressure of water vapor (H2O) in the mixture to the saturated vapor pressure of water at a given temperature

  • Function of both water content and temperature.

  • Relative humidity is the amount of water vapor present in the air divided by the maximum amount that the air could contain at that temperature.

  • Relative humidity is expressed as a percentage.

  • RH is 100% if the air is saturated with water vapor and 0% if no water vapor is present in the air at all.

Specific Humidity

  • Specific humidity (or moisture content) is the ratio of water vapor mass to the air parcel's total (i.e., including dry) mass

  • Also known as humidity ratio

  • Does not change with expansion or compression of air parcel

  • It is grams of water vapor per kilogram of air.

Mixing Ratio

  • Specific humidity is approximately equal to the "mixing ratio"

  • Ratio of the mass of water vapor in an air parcel to the mass of dry air for the same parcel.

Vapor Pressure

Measures water vapor content of air using partial pressure of the water vapor in the air

Image of Vapor Pressure

Image of Vapor Pressure

Image of Vapor Pressure