How does altitude affect the composition of air?

Altitude affects the composition of air by decreasing the density and pressure of gases as altitude increases.

The composition of air at sea level is approximately 78% nitrogen, 21% oxygen, and 1% other gases, including argon, carbon dioxide, neon, helium, and methane. However, as you ascend in altitude, the composition of air changes. This is primarily due to the decrease in air pressure and density.

Air pressure is the force exerted by the weight of air molecules above a given point. At sea level, air pressure is at its highest because the weight of the air above is greatest. As you ascend, the weight of the air above decreases, thus reducing the air pressure. This decrease in air pressure affects the density of the air, which is the number of air molecules in a given volume. As the pressure decreases, so does the density, meaning there are fewer air molecules in the same volume of space.

This decrease in density and pressure affects the composition of the air. The proportion of oxygen molecules, for example, decreases with altitude. This is why climbers at high altitudes often need to carry supplemental oxygen. The lower oxygen levels can make it harder for the body to function effectively, leading to symptoms of altitude sickness.

However, it's important to note that while the density and pressure of the air decrease with altitude, the proportion of different gases remains relatively constant. This is known as the 'constant composition of dry air'. It means that even at high altitudes, the air is still about 78% nitrogen and 21% oxygen. The key difference is that there are simply fewer molecules of each gas present.

In summary, while the overall composition of air in terms of the proportion of different gases remains relatively constant with altitude, the density and pressure of the air decrease, meaning there are fewer molecules of each gas present. This can have significant effects on the body and its ability to function effectively at high altitudes.