How is relative humidity defined?

Relative humidity is defined as the ratio of the actual water vapor pressure in the air to the maximum saturation pressure at a given temperature, expressed as a percentage. This means it indicates how close the air is to being fully saturated with moisture. When relative humidity is at 100%, the air is completely saturated, and no more water vapor can be held, leading to condensation.

This concept is vital in various applications, particularly in painting, where understanding humidity levels is critical for the proper application of paints and coatings. High relative humidity can affect the drying time and adhesion properties of paint, while low humidity can lead to rapid drying, which might not be ideal for all paint formulations.

The other definitions, while related to moisture, do not accurately capture the nuanced relationship between actual water vapor and saturation pressure that defines relative humidity, making them less precise in this context.