Which type of air is more dense?

Dry air is denser than humid air due to the difference in molecular weight of the gases that make up the air. Air consists primarily of nitrogen and oxygen, which are heavier molecules compared to the water vapor present in humid air. When water vapor enters the atmosphere, it replaces some of the nitrogen and oxygen in the air. Since the molecular weight of water vapor (H2O) is less than that of nitrogen (N2) and oxygen (O2), this replacement decreases the overall density of the air mixture.

Additionally, temperature plays a significant role in air density. Cold air tends to be denser than warm air because colder molecules are more tightly packed together, while warmer molecules have more energy and tend to spread out. However, the distinction between humid and dry air directly influences density, with dry air being denser because it has a higher proportion of heavier nitrogen and oxygen molecules relative to the lighter water vapor.

In summary, dry air is more dense because it lacks the lighter water vapor, allowing for a higher concentration of heavier gas molecules. This principle is particularly important for pilots, as air density affects aircraft performance, including lift and engine performance.