Table 7a-1: Average composition of the atmosphere up to an altitude of 25 km.
Gas Name
|
Chemical Formula
|
Percent Volume
|
Nitrogen
|
N2
|
78.08%
|
Oxygen
|
O2 |
20.95%
|
*Water
|
H2O |
0 to 4%
|
Argon
|
Ar |
0.93%
|
*Carbon Dioxide
|
CO2 |
0.0360%
|
Neon
|
Ne |
0.0018%
|
Helium
|
He |
0.0005%
|
*Methane
|
CH4 |
0.00017%
|
Hydrogen
|
H2 |
0.00005%
|
*Nitrous Oxide
|
N2O |
0.00003%
|
*Ozone
|
O3 |
0.000004%
|
* variable gases
from http://www.physicalgeography.net/fundamentals/7a.html