What is Relative Humidity?
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?
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?
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?
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.
Measure Relative Humidity
- Extech 44550 Pocket Humidity & Temperature Pen
- Extech 445580 Humidity & Temperature Pen
- Extech EasyView Hygro-Thermometer
- Kestrel 3000 Pocket Weather Meter
- Vaisala HM70 Handheld Humidity Meter
- Vaisala HMP60 Humidity and Temperature Sensor
- Vaisala HMP155 Humidity and Temperature Sensor
- RM Young 41382 Humidity and Temperature Sensor
- Lufft WS300 Multi-Parameter Weather Sensor
- NexSens DS9300 Temperature & Humidity Kit