Introduction to humidity, relative humidity, and dew point

What is humidity?

Humidity is the amount of water vapour present in the atmosphere. The amount of humidity depends on air temperature and pressure, typically it is very between 2-5%. Th 99 percent of the water vapour resides within the troposphere.

Types of humidity

 There are three types of humidity: 

1. Absolute humidity 

2. Specific humidity

 3. Relative humidity

What is Absolute humidity?

Absolute humidity is the actual amount of water in the air. It is measured in milligrams per liter.

What is specific humidity? 

specific humidity is the amount of water vapor per gram of air. Specific humidity does not change with air temperature and pressure.

What is relative humidity? 

At a given temperature, relative humidity is the amount of water vapour present in the unit volume of air. 

For example: For a given temperature of 30 degrees, the maximum vapor capacity of air is 1000 gram and the present amount of vapour is 500 grams. The relative humidity is calculated as

How temperature and humidity are related?

When temperature increases, the vapour capacity of air also increases because air expands by which air can now hold more moisture. For above example, suppose that temperature rises to 40 and air vapour holding capacity increases to 1300 grams. If no more moisture is added to the air, then relative humidity is

When the temperature drops, the air starts shrinking. Which reduces the vapour holding capacity of air. For the above example, suppose that temperature decreases to 20 degree and  maximum vapour holding capacity of the air reduces to 750 gram. If no more vapour is added to the air, then relative humidity is

This is why dew often forms at night or early morning. because at this time the temperature of the air falls and the amount of water vapor that air can hold decreases. The excess water vapor then condenses into small drops on whatever it touches.

What is the dew point?

The dew point is the temperature at which air cannot store more moisture i.e. air is full of moisture. In other words, the dew point indicates the temperature at which the air becomes 100 percent saturated.

What Is the difference between relative humidity and dew point?

Relative humidity is a percentage that indicates how saturated the air is. While dew point is the temperature at which the air becomes saturated with water vapor.

How is humidity measured?

A hygrometer is a device that measures the humidity. A dew point hygrometer measures the dew point temperature.

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