HUMIDITY

Humidity-: Humidity is the amount of water vapour in the air. If there is a lot of water in the air , the humidity will be high.

                               In simple words , humidity means water vapour in the air, but not to be liquid droplets in the fog , clouds,or rain. Higher Humidity reduces the effectiveness of sweating in cooling the body by reducing the rate of evaporation of moisture from the skin. The gaseous state of water, is generally invisible to the human eye. Humidity indicate the likelihood for precipitation, dew or fog to be present.  The amount of water vapour needed to achieve saturation increase as the temperature increases.

There are three types of humility-:

1. Absolute humidity 

2. Relative humidity 

3. Specific humidity 

1. Absolute humidity -: Absolute humidity is the measure of water vapour or moisture in the air, regardless of temperature.  It is expressed as grams of moisture per cubic meter of air ( g/m^3). 

                    In other words , the total mass of water vapour present in a given volume of the mass of the air known as " absolute humidity ". It does not take temperature into consideration. Absolute humidity in the atmosphere ranges from near zero to roughly 30 grams per cubic meter when the air is saturated at 30 °C. It is the mass of water vapour divided by the volume of the air and water vapour mixture, which can be expressed as -

Absolute humidity = mH2O / V(net)                                                                 

The absolute humidity changes as air temperature or pressure changes , if the volume is not fixed.

2. Relative humidity -: Relative Humidity is actual amount of moisture in air at any given temperature,  divided by the greatest amount of moisture the same air could hold without condensation. Relative humidity could also be expressed by moisture, divided by the highest vapour pressure ( saturation condition ) possible under the same conditions. 

                 Highest pressure that water vapour can have without condensation,  i.e. ,100 % relative humidity at various atmospheric temperature. 

3. Specific humidity -: Specific humidity is the ratio of the mass of water vapour to the total mass of the air parcel. Specific humidity is approximately equal to the mixing ratio,which defined as the ratio of the mass of water vapour in an air parcel to the mass of dry air for the same parcel. As the temperature decreasing the amount of the water vapour needed to reach saturation also decreases. As the temperature of a parcel of air become lower it Will eventually reach the point of saturation without adding or losing water mass.