Humidity & Types

Humidity is the measure of the amount of airborne water vapour. The amount of water vapour in the air is measured as humidity. Absolute, relative, and specific humidity are the three most common types of humidity measurements. The humidity reading reveals how much moisture or water vapour is present in the air.

Types of Humidity

Absolute Humidity

The actual amount of the water vapour present in the atmosphere is known as the absolute humidity.
It is the weight of water vapour per unit volume of air and is expressed in terms of grams per cubic metre.
The absolute humidity differs from place to place on the surface of the earth.
The ability of the air to hold water vapour depends entirely on its temperature (Warm air can hold more moisture than cold air)

Relative Humidity

The percentage of moisture present in the atmosphere as compared to its full capacity at a given temperature is known as the relative humidity.
Relative Humidity = [Actual amount of water vapor in air (absolute humidity)/humidity at saturation point (the maximum water vapor air can hold at a given temperature)] X 100
With the change of air temperature, the capacity to retain moisture increases or decreases and the relative humidity is also affected.
Relative humidity is greater over the oceans and least over the continents (absolute humidity is greater over oceans because of greater availability of water for evaporation).
The relative humidity determines the amount and rate of evaporation and hence it is an important climatic factor.

Specific Humidity

It is expressed as the weight of water vapour per unit weight of air.
Since it is measured in units of weight (usually grams per kilogram), the specific humidity is not affected by changes in pressure or temperature.

Absolute Humidity and Relative Humidity are Variable whereas Specific Humidity is a constant.

Dew point

The air containing moisture to its full capacity at a given temperature is said to be saturated.
It means that the air at the given temperature is incapable of holding any additional amount of moisture at that stage.
The temperature at which saturation occurs in a given sample of air is known as dew point.
Dew point occurs when Relative Humidity = 100%.

Condensation

The transformation of water vapour into water is called condensation.
Condensation is caused by the loss of heat (latent heat of condensation, opposite of latent heat of vaporization).
When moist air is cooled, it may reach a level when its capacity to hold water vapour ceases (Saturation Point = 100% Relative Humidity = Dew Point reached).
Then, the excess water vapour condenses into liquid form. If it directly condenses into solid form, it is known as sublimation.

Condensation can take place when the dew point is

lower than the freezing point,
higher than the freezing point.
White frost, snow and some clouds (cirrus clouds) are produced when the temperature is lower than the freezing point.
Dew, fog and clouds result even when the temperature is higher than the freezing point.
Forms of condensation may also be classified on the basis of their location, i.e. at or near the earth’s surface and in free air.

Effects of Humidity

Humidity can cause various uncomfortable conditions, let’s discuss these one-by-one:

Bacteria and viruses spread easily in humid conditions because of which people often fall sick, especially from respiratory issues.
When the relative humidity goes above 60%, the viruses spread among people, and they get ill.
The rise in the moisture content of air leads to the rise in temperature because of which the evaporation rate of sweat from our bodies slows. This slowdown leads to the following problems:

Overheating in our bodies
Exhausts easily, and
Consequences are lethal to health like Altered blood circulation, increased respiration rate, and sweating.
During humidity, higher levels of dust mites and fungi lead to allergies among people.
The spread of airborne chemical contaminants.
Detrimental to asthma sufferers.

Humidity & Types

Also Read : Seasonality by Motion of Earth