Atmospheric Composition


Gas Name          Chemical Formula   Percent Volume


Nitrogen N_2 78.08% Oxygen O_2 20.95% *Water H_2O 0 to 4% Argon Ar 0.93% *Carbon Dioxide CO_2 0.0360% Neon Ne 0.0018% Helium He 0.0005% *Methane CH_4 0.00017% Hydrogen H_2 0.00005% *Nitrous Oxide N_2O 0.00003% *Ozone O_3 0.000004%

Notes

  1. The table shows the composition by volume averaged over lower 25 km of the atmosphere.

  2. Gases which are variable are marked by asterisks.

  3. Recall the ideal gas law PV=NkT, where P is pressure, V is Volume, N is particle density, k is Boltzmann's constant, and T is Kelvin Temperature. Insofar as the ideal gas law is valid and P and T can be regarded as mean values, then for each component i we have P_iV=N_ikT. Thus, V_i/V=N_i/N. Thus the composition by volume is roughly the composition by number fraction.

  4. Michael J. Pidwirny Fundamentals of Physical Geography.