Capacity of Air

The Composition of the Atmosphere  
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.