In terms of density altitude, which condition causes the highest density altitude?

Density altitude refers to the altitude at which the air density is equivalent to a standard atmosphere. It is affected by temperature, pressure, and humidity. Higher density altitude indicates thinner air, which can impact aircraft performance and other aviation operations.

High humidity contributes to a higher density altitude because moisture in the air is less dense than dry air; water vapor (H2O) is lighter than the nitrogen and oxygen that make up the majority of the atmosphere. As humidity rises, the weight of the air decreases, leading to a reduction in air density and resulting in an increase in density altitude.

In contrast, lower temperatures and higher pressures both contribute to higher air density, which lowers density altitude. Similarly, lower altitudes will naturally have higher air density, resulting in lower density altitudes. Therefore, high humidity is indeed the condition that causes the highest density altitude, making it the correct choice.