How is relative humidity defined?

Relative humidity is defined as the amount of moisture present in the air compared to the maximum amount of moisture that the air can hold at a specific temperature, expressed as a percentage. This concept reflects the current humidity level relative to the air's saturation point, which is influenced by temperature. When air is fully saturated, it cannot hold any more moisture, and the relative humidity reaches 100%.

Understanding relative humidity is crucial in various contexts, such as weather forecasting, building inspections, and HVAC system performance, because it affects how comfortable we feel and can impact building materials and air quality. High relative humidity can lead to issues such as mold growth, while low relative humidity can result in dry air conditions that may damage wood or increase respiratory discomfort.

The other options present definitions that do not align with this scientific understanding. Total moisture in the air refers to absolute humidity, which measures the actual amount of water vapor per unit volume but does not take temperature into account. Absolute humidity specifically quantifies the moisture without referring to saturation levels. Humidity that changes with temperature refers more to how relative humidity can fluctuate as temperatures rise or fall, but it does not define what relative humidity itself is.