Relative Humidity

Fondriest Environmental Science Library
Fondriest Environmental Inc.
Relative humidity is a measure of the amount of moisture in the air relative to the total amount of moisture that the air can hold.

Relative humidity is a measure of the amount of moisture in the air relative to the total amount of moisture that the air can hold.

 

What is Relative Humidity?

Humidity makes clouds, precipitation, and fog possible.

Humidity makes clouds, precipitation, and fog possible.

Relative humidity is a measure of the amount of moisture in the air relative to the total amount of moisture that the air can hold.   For instance, if the relative humidity is 50%, then the air is only half saturated with moisture.  Warmer air can hold more moisture than colder air.

Why is relative humidity important?

Relative humidity is reported as a percentage.

Relative humidity is reported as a percentage.

Without humidity, there would be no clouds, no precipitation, and no fog.  Humidity is simply water vapor in the air, which is needed to form rain.  Additionally, water vapor holds heat in the air.  It is a greenhouse gas, which means it is a gas that absorbs heat and warms the atmosphere.  This is why humid air feels warmer.

How is it reported?

A capacitance sensor will change shape in different humidity causing the total capacitance to change which can then be converted to relative humidity.

A capacitance sensor will change shape in different humidity causing the total capacitance to change which can then be converted to relative humidity.

Relative humidity is reported as a percentage of the total amount of moisture that could be held in the air.  For instance, if the air is only half saturated with water vapor, the relative humidity will be reported at 50%.  If the air holds all the water vapor it can hold, it is 100% saturated.

How is it measured?

Relative humidity is influenced by temperature and location.

Relative humidity is influenced by temperature and location.

A capacitance-type sensor is commonly used to measure relative humidity.  Changes in relative humidity cause the shape of the sensor to change.  When the sensor changes shape, it’s capacitance, or ability to store an electrical charge, changes in a detectable and repeatable fashion.

What factors influence it?

Relative humidity is influenced by temperature and geographic location.  Warmer air holds more moisture than cooler air, and warmer weather promotes evaporation. Areas with a lot of surface water, such as coastal areas and the Great Lakes region, have high humidity levels due to evaporation.  Humidity is especially high in warm, tropical areas.