Oxygen in the Atmosphere:

Gases in Air

As elevation increases, air pressure decreases. To figure out how this affects the workers at the ALMA Observatory, we need to consider the types of gases in the air: in particular, oxygen.

Air is a mixture of gases: about 78% nitrogen (N2), 21% oxygen (O2), and small amounts of other gases. The percentages of the gases in the air are the same at any elevation. For example, the percentage of oxygen is 21% whether you’re at sea level or in the mountains.

Oxygen is a gas that our bodies need to function. You’ll learn more about the importance of oxygen in the “Oxygen in the Body” tab.
Ring chart titled 'Composition of dry air, by volume'; 78% nitrogen, 21% oxygen, 1% argon, carbon dioxide, methane, and other gases.
Figure 3. The percentages of different gases in dry air, by volume.