How is the relative humidity of an unsaturated air mass affected by temperature changes?

When considering how the relative humidity of an unsaturated air mass is affected by temperature changes, it's essential to understand the relationship between temperature, the capacity of air to hold water vapor, and relative humidity itself.

Relative humidity is defined as the amount of water vapor present in the air compared to the maximum amount of water vapor that the air can hold at a given temperature, expressed as a percentage. As temperature rises, the capacity of the air to hold water vapor increases. This means that while the actual amount of water vapor remains constant, the percentage that represents relative humidity decreases.

Therefore, when the temperature increases, the air can hold more moisture without becoming saturated. If the absolute amount of moisture in the air does not change, the relative humidity will drop because the denominator (the maximum capacity for water vapor) increases.

In this context, understanding that when air becomes warmer, unless more water vapor is added, the relative humidity must decrease highlights the correct relationship between temperature and relative humidity changes.