# Absolute Humidity, Specific Humidity & Relative Humidity YouTube Lecture Handouts

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Watch Video Lecture on YouTube: Absolute Humidity, Relative Humidity, Specific Humidity & Mixing Ratio

Absolute Humidity, Relative Humidity, Specific Humidity & Mixing Ratio

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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

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