Relative Humidity & Dew point

Moist air refers to a mixture of dry air and any amount of watervapor, when there is no watervapor in the air, it is call dry air.

Absolute humidity is amount of water vapor present in a unitvolume of air.

Saturated humidity refers to the maximum amount of water vapor that a unit volume of air can contain at a certain pressure and temperature.

Relative Himidity(R.H.),is the ratio of the partial pressure of water vapor in an air-water moisture to the saturated vapor pressure of water at a prescribed temperature.

R.H. =Absolute humidity / Saturated humidity X 100%.

For example:In a normal environment,if the actual water desityis 30g in one cubic meter, at 35℃ compared to the saturation vapor density (saturated humidity) at that temperature of 39.2g per cubic meter, then the relative humidity is R.H.=30/39.2 x 100%=76.5%. 

Dewpoint or dewpoint temperature is the temperature at which the water vapor in air at constant barometric pressure condense into liquid water at the same rate at which it evaporates. At temperatures below the dew point, water will leave the air. The condensed water is called dew when it forms on a solid surface.A high relative humidity indicates that the dew point is closer to the current air temperature. Relative humidity of 100% indicates the dew point is equal to the current temperature and that the air is maximally saturated with water.