Based on the Greek term “atmos” = vapour and “sphaira” = ball, the word originally describes the layer of gas surrounding the terrestrial sphere.
1. The layer of air surrounding the earth with the characteristic composition of:
- 78 % nitrogen (N2)
- 21 % oxygen (O2)
- 0.9 % argon (Ar)
- 0.04 % carbon dioxide (CO2)
- Tracer gases
- Variable proportion of water vapour 0 - 40 g water vapour per kg of air.
- “Atmospheric pressure" means the air pressure under normal conditions on the ground. Except on high mountains, it is around 1000 hectopascal [hPa]. 1 Pascal [Pa] is 1 N/m².
2. The atmospheres of other celestial bodies have completely different compositions and pressures.
3. “Atmosphere” is also understood to mean the gas environment of a chemical or physical process. In a closed room, it can have a completely different composition than in natural atmosphere. In pressure or vacuum chambers, the pressure of the technical atmosphere can differ from the natural atmospheric pressure by the factor of 10-15 up to several 1,000.