The atmosphere is a thin layer of gases. There are four main gases excluding water and other trace gases. The table below shows the compostion by percentage of the atmosphere.
| Gas | Percentage |
|---|---|
| Nitrogen (N2) | 78.08% |
| Oxygen (O2) | 20.95% |
| Argon (Ar) | 0.934% |
| Carbon dioxide (CO2) | 0.036% |
The above percentages are by volume. Water normally is 1-3% by volume but can be anywhere between 0.1 and 5%. The compostion of air always excludes water because it's concentration varies so much.
Other important gases are the remaining Noble Gases (Argon is a major constituent of the atmosphere). These gases are inert so do not exist in compounds (with the exception of Xenon). Therefore the atmosphere is the only source of these elements. Their percentages in dry air are given below:-
| Noble Gas | Percentage |
|---|---|
| Neon (Ne) | 1.82x10-3 % |
| Helium (He) | 5.24x10-4 % |
| Kypton (Kr) | 1.14x10-4 % |
| Xenon (Xe) | 8.70x10-6 % |
There are many other gases present in the atmosphere in very small concentrations. These are called Trace Gases.
The pie chart below shows the composition of the atmosphere. It shows that the trace gases make up a very small percentage of the atmosphere but they are still vital!