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Absolute Humidity

Rahul Thadani Apr 20, 2019
Humidity or moisture is one of the key regulators of the climate and there are three ways to express the humidity in the environment. Absolute humidity is one way, you will understand how it is different from other types of humidity and how it is measured.
Absolute humidity is defined as the amount of water vapor present in a unit volume of air, usually expressed in kilograms per cubic meter.
Whenever you hear a weather report there is mention about the humidity of the atmosphere. It is one of the main meteoric factors considered while predicting rainfall or thunderstorm. It is also one of the external factors that affect the bio-diversity of a region.
The higher the humidity greater the discomfort for humans due to the reduced effectiveness of sweating. Humidity can be expressed or measured in three different ways; as absolute, relative and specific. While absolute humidity is an exact value, relative humidity is expressed in percentage and specific humidity is measured as a ratio.

What is Absolute Humidity?

This gives a precise measurement of the amount of water vapor present, and thus enables the calculation of the percentage of humidity in the atmosphere. While expressing this parameter the amount of grams of water vapor present in each cubic meter of air need to be specified.
The saturated water vapor density depends on the pressure of the gas; therefore, the maximum mass of vapor per unit volume also depends on the air pressure. As the pressure, and, therefore, the temperature, affects absolute humidity, it is inconvenient to use this as an engineering quantity.
A higher amount of absolute humidity present in the atmosphere means that people will feel hotter when they are outdoors. This happens because the greater amount of water vapor in the air results in lesser amounts of perspiration, or sweat, being evaporated from a person's body.
As a result, the cooling effect of the evaporation of perspiration is negated. It also indicates the likelihood of dew, fog or precipitation that may occur.

Measuring Humidity

The most common device to measure humidity is known as a hygrometer, or a psychrometer. Remotely placed satellites are used to measure humidity globally. These satellites can detect the water vapor concentration in the atmosphere through sensors that are sensitive to infrared radiation.
They play a very important role in observing the climate conditions and in major weather forecasts. Interestingly, some buildings also use a device known as a humidistat. These are used along with a thermostat (which carries out temperature control in the building), in order to regulate the amount of humidity that is present inside that specific building.
For conversion, the following formula is used.

Habs = (Hsat)(RH/100)

Habs = Absolute humidity,
Hsat = Saturation humidity, and
RH = Relative humidity at the same temperature.

By using this method, forecasters can calculate both the levels for any given day or time.

Difference between Absolute, Relative and Specific Humidity

Relative humidity is another way of measuring the amount of water vapor present in the air. It is the ratio of amount of moisture present in the atmosphere, at any given point in time, to the amount of moisture that would be in the air if the moisture was completely saturated, at the same temperature.
So, while absolute humidity is an exact measure of the amount of moisture, relative humidity is the comparison of this amount with another amount. Whereas specific humidity is the mass of water vapor in the unit mass of moist air.
It is this relative humidity that weather forecasters display on their reports. Absolute value is the measurement that they use in order to derive the percentage of relative humidity in the air. Forecasters thus create a table for one entire day, and arrive at an average figure in order to calculate the relative value in the form of a percentage.
The ideal relative humidity value for human beings is between 30% and 60%. If it is more than this range, perspiration of human beings will be ineffective and they will feel hotter. If it is less than this amount, humans will suffer from excessive thirst and dry skin. Thus, humidity is important for water to be maintained in the atmosphere.