One of the most frequently used terms in meteorology and weather reports is relative humidity . Although we hear it daily on television and radio, few of us know what it means.
The term relative humidity simply means the capacity of the air to absorb more moisture.
Let's say you hear in a weather report that the relative humidity is 40%. This means that, of the possible humidity the air could have under the prevailing conditions (pressure and temperature), it only has 40%.
As you may have noticed, air cannot hold an unlimited amount of moisture. Therefore, on a foggy day with 100% relative humidity, if a person perspires, it is very difficult for the perspiration to evaporate. This slows down the elimination of body heat, causing hot flashes and general discomfort.
When relative humidity reaches 100%, it is known as the saturation point.
Like all materials, air also has a limit to absorb moisture. Imagine that you have spilled a glass of water on the table and you want to dry it with a cloth. Depending on what material the cloth is made of, it can absorb more moisture than another made of another material, but there comes a time when it can no longer collect more water and you must wring it out.
The same thing happens with the air, and when this point is reached, it no longer has the capacity to receive moisture, and the water vapor condenses, commonly causing phenomena such as dew, fog, mist or frost.
The difference between relative humidity and absolute humidity is that the former is a percentage measure, that is, what percentage of the water that the air can hold, it has; whereas absolute humidity is a measure of the amount of water by weight that the air contains, and is used to represent it in grams or kilograms.
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