What is a primary effect of increased altitude on air density?

As altitude increases, the primary effect on air density is a decrease in air density. This phenomenon occurs because the atmosphere becomes less compressed at higher elevations. At lower altitudes, the weight of the air above exerts pressure on the layers below, causing air molecules to be more densely packed together. However, as you ascend, there is less overlying air pressure, which allows the air to expand and results in fewer air molecules per unit volume. Consequently, at high altitudes, the air becomes less dense, which has significant implications for aircraft performance, including lift, engine power, and overall flight characteristics. Understanding this relationship is crucial for pilots when planning and executing flight maneuvers in different altitudinal environments.