Humidity

-a quantity representing the amount of water vapor in the atmosphere.

• It is measured using a hydrometer.
• The wet and dry bulb thermometer is also known as a psychrometer.
• Weather satellites can also measure the amount of humidity in the atmosphere.
• A hygrometer measures the humidity in the atmosphere using two thermometers: dry and wet bulb thermometers.
• The wet bulb thermometer is wrapped in thin muslin and dipped in a container of water to keep the muslin cloth wet.
• If the air is dry water evaporates from the muslin and cools such that the mercury contracts.
• The dry bulb is not affected hence the two show different readings.
• The wet bulb shows a low reading whilst the dry bulb shows a higher reading.
• Depression/Difference=the reading of the dry bulb less the reading of the wet bulb thermometer.
• The humidity is then found by reading humidity tables. For example if there is no difference between the two readings the humidity is 100%
• Electronic hygrometers are also used. These are easier to read.
• Relative humidity is measured in percentage terms.

Types of humidity
There are several ways to measure and express humidity:

1. Absolute Humidity-the total mass of water vapor present in a given volume of air.
2. Relative Humidity-the amount of water vapor in a given volume of air at a given temperature.
3. Specific Humidity-the ration of the mass of  water vapor to the mass of the parcel of air.

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