What is Humidity?

Humidity is water vapor present in the atmosphere is known as Humidity.

Vapor pressure

When water vapor mixes with other gases of atmosphere, it exerts a pressure in all direction as do the other gases.

This partial Pressure exerted by vapor is known as the vapor pressure.

Saturated vapor pressure

When air contains all the moisture that it can hold to its maximum limit, it is called saturated air and the vapor pressure exerted by this air is called saturated vapor pressure.

Relative Humidity (RH)

Relative humidity represents the amount of water vapor actually present in air compared with the maximum amount of vapor can be held same air at a given temperature.

Actual quality of water vapor present in a given volume of air

RH= —————————————————————————————————- X 100

Maximum amount of water vapor the same volume of air can hold

Specific Humidity

Specific humidity is defined as the ratio of mass of water vapor to the given mass of air contacting the moisture

Thus it will be measure in grams of water vapor per kg of air.

Maximum ration = MV/Ma

where

MV : Mass of water vapor

Ma : Mass of dry air

Mixing ration : It is the ration of the mass of water vapor to the mass of dry air

Absolute Humidity (AH)

Absolute humidity is defined as the ratio of actual mass of water vapor present to the total volume of moist air in which it is contained.

It is measured in grams per cubic meter of air or in terms of partial pressure of water vapor in air in mbor mm mercury.

AH = Weight of water vapor / Volume of air

Psychometric

Measurement of humidity with different instruments is called psychometric