What is the impact of high humidity on density?

High humidity affects the density of air by making it lighter. This may seem counterintuitive, but when humidity increases, water vapor replaces some of the nitrogen and oxygen molecules in the air, which are heavier gases.

Water vapor has a lower molecular weight (approximately 18 g/mol) compared to the nitrogen (approx. 28 g/mol) and oxygen (approx. 32 g/mol) that it displaces in the air. As a result, the overall density of the humid air decreases. Therefore, in a humid environment, even though the amount of air may increase in terms of mass due to moisture, the presence of lighter water vapor decreases the density of the overall air mix.

This concept is crucial for understanding meteorological phenomena and is particularly relevant for aviation, as changes in air density can significantly affect aircraft performance and operations.