Which atmospheric conditions would increase density altitude?

High temperature and low pressure contribute to an increase in density altitude. Density altitude is an important concept in aviation that refers to the altitude in the atmosphere where the air density is equivalent to that at a specific configuration, usually referring to standard pressure and temperature conditions.

As the temperature rises, the air becomes less dense because warmer air molecules are more energetic and tend to spread apart. This results in a decrease in the number of air molecules in a given volume, which means that even at a physically low altitude, the effective density is reduced.

Simultaneously, low pressure means that there are fewer air molecules in the atmosphere overall, which compounds the effect of temperature on air density. When both conditions are present—high temperatures and low pressure—the result is significantly increased density altitude. This can affect aircraft performance dramatically, as engines produce less power, wings generate less lift, and propellers become less efficient in less dense air.

Conditions such as low humidity and high pressure, or cool temperatures accompanied by high winds, won't have the same impact on density altitude. Low humidity generally contributes to higher air density, while high pressure also helps to increase air density, therefore reducing density altitude.