What is Air Made of?

All plants and animals on Earth need oxygen to survive, yet the amount of free oxygen (O₂) available in the air and water is very small compared to the total amount of air or water. In particular, only 20.946% of Earth's atmosphere is O₂.

(In aquatic environments, the concentration of oxygen is even lower--only between 5 mL/L and 9 mL/L depending on the temperature and salinity. Oxygen dissolves better in colder, fresher water.)

The remainder of Earth's air is nitrogen (N₂), water vapor, and trace gases. Below is the list of compounds that make up the atmosphere.

Composition of Air:

Listed from most plentiful to least abundant.

Nitrogen, N₂..................... 78.084%
Oxygen, O₂...................... 20.946%
Argon, Ar......................... 0.9340%
Water, H₂O...................... 0.4% overall, as high as 4% near surface
Carbon Dioxide, CO₂.......... 0.039%
Neon, Ne......................... 0.001818%
Helium, He....................... 0.000524%
Methane, CH₄................... 0.000179%
Krypton, Kr....................... 0.000114%
Hydrogen, H₂.................... 0.000055%
Nitrous Oxide, N₂O............ 0.00003%
Carbon Monoxide, CO......... 0.00001%
Xenon, Xe........................ 0.000009%
Nitrogen Dioxide, NO₂........ 0.000002%
Iodine, I₂......................... 0.000001%
Ozone, O₃........................ up to 0.000008%, mostly in the stratosphere
Ammonia, NH₃.................. less than 0.000001%

All percentages are by volume, not by weight.

© Had2Know 2010