Both humidity and relative humidity refer to the amount of water vapour in the air, however, they are not the same. Humidity is the absolute amount of water vapour in the air, whereas relative humidity is the amount of water vapour in the air in comparison to the maximum amount of water vapour the air might hold at that temperature and pressure. As a result, relative humidity considers air temperature and pressure, whereas humidity does not.
In Pharmaceuticals RH is an important factor to determine the Quality of products. The RH is maintained through Pharmaceutical HVAC System.
Basic Difference between Humidity and Relative Humidity
Humidity: Humidity refers to the amount of H2O vapor in the environment. In general, the evaporation of water from water bodies is caused by sun radiation in the air. This evaporation produces water vapor, which mixes with the air.
Relative Humidity: It is a measurement of water vapor that is relative to the air temperature and pressure. It’s calculated as a %age of the total amount of water vapor in the air that might be held at the current temperature and pressure. Warm air can hold more water vapor as compared to cold water
Causes Behind Change in RH and Humidity
Cold air holds less moisture as compared to hot air. So the Relative Humidity of cold air will be higher than warm air, eg. 20°C air can hold up to 10 gm vapor, then relative humidity will be 100%, and if there increase the temperature to 21°C then the air holding capacity of water vapor will also increase, and RH will decrease.
Since warm air can hold more water vapor than cold water. if we lower the temperature then RH will go up.
Useful Thumb Rule to Remember Facts Between Temperature, RH, and Pressure:
The first law is that as the temperature rises, the air becomes dry (RH down), and as the temperature falls, the air becomes wet (RH up). When it comes to pressure, the general rule is that as pressure drops, the air becomes dry (RH drops), and as pressure rises, the air becomes wet (RH rises).
Types of Humidity with Explanation
Humidity is mainly of three types: Relative, Absolute, and Specific.
Relative Humidity: It is a measurement of water vapor that is relative to the air temperature. It’s calculated as a %age of the total amount of water vapor in the air that might be held at the current temperature.
Absolute Humidity: Absolute humidity is the actual amount of water vapor or actual mass of water vapor in air volume without consideration of temperature. absolute humidity is expressed in grams per square cubic meter gm/m3.
Comparison Table between Humidity vs Relative Humidity
Humidity Role in Pharmaceuticals and its Importance
It is an important factor in pharmaceuticals to maintain the quality of products from starting to the final stage. The reason for monitoring the RH is to control the moisture at the site where the product is being manufactured. if RH goes up from the required condition, it can harm the products or degrade the potency of products over time for long periods.
Humidity is also a significant issue for products that are extremely sensitive to moisture, such as Pharmaceuticals drugs. This is because it can change the product’s qualities so that it’s no longer useful. That is the reason why medical pills and dry powders are kept in controlled environments with specific humidity and temperature levels.
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