In the field of physics, humidity represents the quantity of water moisture present in the atmosphere. The humidity can be seen by the naked eye but can be estimated by using certain methods.
Humidity indicated the weather forecast efficiently. Furthermore, it is classified into two kinds, namely, Absolute and Relative humidity.
Key Takeaways
- Absolute humidity measures water vapor content in the air regardless of temperature.
- Relative humidity considers both water vapor content and air temperature.
- A high relative humidity can make a warm day feel hotter, while a low relative humidity can make a cold day feel colder.
Absolute vs Relative Humidity
Absolute humidity is the actual amount of water vapour in the air, measured in grams of water vapour per cubic meter of air. The relative humidity is a percentage that expresses how much water vapour the air is holding compared to the maximum amount it could hold at a particular temperature.
When manifesting the atmosphere’s absolute humidity, it ignores the temperature factor. In simple words, Absolute humidity is a criterion of how considerably the rate of water vapour is subdued in a given amount of air during that time.
The volume of air and water vapour are divided to obtain absolute humidity.
On the contrary, Relative humidity is defined as the ratio between the vapour pressure equilibrium for water in a given solvent and the partial fraction of water vapour in the solvent.
Here, the temperature condition is taken into account while calculating the relative humidity of the atmosphere. The relative humidity is always in percentage.
Comparison Table
| Parameters of Comparison | Absolute Humidity | Relative Humidity |
|---|---|---|
| Definition | Water vapor content is used as a measurement of absolute humidity in a given volume of air. | It is the partial percentage of the stable vapor pressure of water by the level of water vapor in that given mixture. |
| SI unit | The absolute humidity is expressed in the form of moisture in grams or kilograms per cubic meter of the given air. | It results in a percentage value. |
| Temperature role | The absolute humidity is irrelevant to the temperature available in the atmosphere at that point. | Relative humidity relies on the temperature of the atmosphere, such that relative humidity is inversely proportional to the temperature. |
| Affected by area | The circumstances of the planet affect absolute humidity, such as seasons, land, and water. | In coastal areas, relative humidity is more, while low in desert areas. |
| Mathematical expression | Absolute humidity can be expressed as the ratio of air volume to water vapor volume. | The relative humidity is calculated by dividing the volume of water vapor and the volume of the dry air |
What is Absolute?
The absolute humidity of the quantity of air in the atmosphere is defined as the quality of water vapour present in the wet air. As a result of the presence of water vapour in humid air, the volume of water vapour is the same as in wet air.
Consequently, absolute humidity is described by its ability to measure water vapour density in a moist atmosphere. Meanwhile, the temperature does not affect absolute humidity.
Furthermore, the symbol of absolute humidity is denoted as ρv. Besides, the value of absolute humidity is not constant, and it changes according to the moisture content of the air at various places.
As a unit of measurement, absolute humidity is defined as the amount of moisture per cubic meter of air (g/m3). Over and above, due to the precise humidity measurement, absolute humidity is considered the most accurate scientific method.
It can be calculated by dividing the mass of the water vapour capacity in the air by the volume occupied by the air.
For instance, if 6 grams of water vapour exists in 2 cubic meters of air, the absolute humidity equals 3 grams/m3.
Due to its precise calculation of how much water is in the air, absolute humidity helps in defining the humidity in the summer, winter, and various seasons.
What is Relative Humidity?
When we speak of relative humidity, we are referring to the ratio of water vapour content in the air compared to how much is needed in order to saturate the air completely.
Moreover, the role of temperature is very important in relative humidity since relative humidity is inversely proportional to the temperature, so when the temperature is increased, the relative humidity of the atmosphere decreases along with it.
Subsequently, the relative humidity remains constant regardless of the amount of air in a space.
And it can be calculated by using the formula; partial percentage ratio between the vapour pressure of pure water over a levelled surface and the water vapour in the mixture.
However, on the other hand, an instrument named a Hygrometer was invented by Swiss physicist and Geologist Horace Bénédict de Saussure in 1783 to calculate relative humidity.
The relative humidity is expressed in percent and denoted by the symbol φ or RH in physics.
The percentage expressed humidity is used as a significant metric while indicating the weather forecasts; in such a way that a higher percentage means the air is humid. Air conditioning and steam turbines are common examples of relative humidity.
Main Differences Between Absolute and Relative Humidity
- Water vapour content is determined by absolute humidity, whereas relative humidity determines the ratio of water vapour to dry air.
- Absolutely doesn’t depend on the temperature, that is, the temperature is neglected while calculating the absolute humidity, whereas the temperature is taken into consideration.
- It is measured in grams or kg/m3 (grams/kilos per cubic meter). And SI unit of Relative Humidity is expressed in percentage.
- The value of absolute humidity is not constant, as it changes along with changes in the amount of water vapour in the atmosphere, while the value of relative humidity is constant, as it contains absolute moisture in the atmosphere.
- Absolute humidity is used to calculate the ratio of the mass of vapour to mass present in the carrier gas stream, while relative humidity is used in weather forecasts to indicate the presence of fogs and mists.
- https://europepmc.org/article/med/1572193
- https://www.tandfonline.com/doi/abs/10.1179/sic.1994.39.Supplement-2.32
Last Updated : 13 June, 2023
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Piyush Yadav has spent the past 25 years working as a physicist in the local community. He is a physicist passionate about making science more accessible to our readers. He holds a BSc in Natural Sciences and Post Graduate Diploma in Environmental Science. You can read more about him on his bio page.
It’s incredible to think that air could have such a quantity of water and how it changes according to the temperature.
I find it very interesting, I am still amazed at how important it is to be able to measure the humidity, I never thought that we could estimate it.
What a interesting article, it’s amazing the world of physics and the impact it has on weather forecasting.
I think it’s remarkable how humidity impacts our perception of temperature. Absolutely fascinating!
This is fascinating!
Wow, this is so useful and enlightening. I never fully understood the differences between absolute and relative humidity before.