What is Relative Humidity?
Atmospheric air is a mixture of various gases and water vapour. The invisible water vapour in the air is called humidity. The amount of water that can be contained in a pound of air depends upon …… temperature of the air pressure of the air At a constant pressure, the warmer the air the amore water vapour it can retain. If air at a certain temperature has absorbed all the moisture it can hold at that temperature, it is said to be saturated. The amount of water present, or the degree of saturation is evaluated in terms of Relative Humidity or Saturation ratio. Hence, Relative Humidity is the actual water content in % of that of a saturated volume. When air is 50% saturated, it contains only one half the amount of water than it can contain at the same temperature and pressure. As the relative humidity approaches 100%, the air can take on less and less moisture and at 100% relative humidity, that air cannot hold more water. If air is saturated with water vapour at a given temperature,
According to our Glossary, “Relative Humidity is the ratio of the existing amount of water vapor in the air at a given temperature to the maximum amount that could exist at that temperature. It is usually expressed in Percent.” The problem with Relative Humidity is that it changes with the temperature so it’s hard to compare versus time. In other words, assuming the temperature is cold at night and hot during the day, the humidity will always be higher at night and lower during the day. The measurement that meterologists prefer is called Dew point. See below.
Air will always contain water vapour. At any given temperature there will be a saturation point at which no more moisture can be retained (any excess will condense). The Relative Humidity of air is the actual moisture content expressed as a percentage of this saturation content. The aim of using silica gel is to keep the Relative Humidity at levels below 50% of the saturation capacity. At these levels, corrosion and mould growth will not be promoted. Problems are often caused if the temperature drops as the saturation content of air at the new temperature becomes much lower.
Many people notice that hot muggy days seem much warmer somehow than days with dry heat. One of the reasons for this is humidity, the amount of water the air holds. When the air holds more water, the basic act of perspiration or sweating is less efficient in cooling down the body. More water in the air means less water can evaporate from the skin, and most people will end up feeling warmer. Some of the ways that humidity is measured is by measuring absolute humidity, and relative humidity, which is often how people tell how “wet” a day will be. First, it’s important to understand that air can only hold a certain amount of water at any given time. This measurement is absolute humidity, and absolute humidity is dependent on the temperature of air. Under many circumstances, the actual air holds far less water than it technically could, so the term relative comes into play. When meteorologists discuss relative humidity they usually do so in percentage amounts, and this percentage is a rati