How does an increase in elevation generally affect air density?

An increase in elevation generally decreases air density due to the decrease in atmospheric pressure that occurs at higher altitudes. As you ascend in elevation, the weight of the air above decreases, which leads to a reduction in air pressure. Air density is defined as the mass of air per unit volume, and as the pressure decreases, the air molecules become more dispersed. This results in fewer air molecules in a given volume, thus lowering the air density.

For instance, at sea level, air is denser because there is more atmospheric pressure compressing the air molecules together. However, as you climb to higher altitudes, such as in mountainous regions or when flying, the air becomes thinner; this tells us that there are fewer air molecules, and consequently, the density is lower. Understanding this relationship is crucial for pilots, particularly as it affects aircraft performance during takeoff, climb, and landing phases.