The Composition of the Atmosphere |
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| Although traces of atmospheric gases have been detected well out into space, 99% of the mass of the atmosphere lies below about 25 to 30 km altitude, whilst 50% is concentrated in the lowest 5 km (less than the height of Mount Everest). | ||
| Component | Chemical Abbreviation | Volume % (dry air) |
| Nitrogen | N2 | 78.08 |
| Oxygen | O2 | 20.98 |
| Argon | Ar | 0.93 |
| Carbon dioxide | CO2 | 0.035 |
| Neon* | Ne | 0.0018 |
| Helium* | He | 0.0005 |
| Hydrogen | H | 0.00006 |
| Krypton* | Kr | 0.0011 |
| Xenon* | Xe | 0.00009 |
| Methane | CH4 | 0.0017 |
| Ozone** | O3 | 0.00006 |
| * Inert gases. ** Strictly speaking, the concentration of ozone in the atmosphere is variable. |
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