Final answer:
Relative humidity measures the amount of water vapor in the air relative to its temperature-dependent maximum. Maximum specific humidity is the concept of the most water vapor air can hold at a certain temperature before reaching saturation. This impacts phenomena like fog formation and the efficiency of drying with hot air.
Step-by-step explanation:
When we discuss humidity in a meteorological context, we are often refer to relative humidity, which indicates the amount of water vapor in the air relative to the maximum amount the air can hold at a certain temperature. Maximum specific humidity is a theoretical concept that represents this capacity, or the maximum amount of water vapor that air can contain at a given temperature before reaching 100% relative humidity and becoming saturated.
The specific humidity is dependent on the air temperature; warmer air can hold more water vapor compared to cooler air. This is why relative humidity commonly increases in the evening as temperatures drop, potentially reaching the dew point where condensation occurs, and fog can form if the condensed water droplets are small enough to stay aloft.
Understanding these principles is essential, for example, in everyday tasks such as drying your hair, where it is more efficient to use hot air that increases the rate of evaporation due to the air's higher capacity for evaporation compared to cold air.