[eweissenbach]

Originally Posted by weeder01

ppmv: parts per million by volume (note: volume fraction is equal to mole fraction for ideal gas only, see volume (thermodynamics))

Gas Volume
Nitrogen (N2)
780,840 ppmv (78.084%)
Oxygen (O2)
209,460 ppmv (20.946%)
Argon (Ar)
9,340 ppmv (0.9340%)
Carbon dioxide (CO2)
394.45 ppmv (0.039445%)
Neon (Ne)
18.18 ppmv (0.001818%)
Helium (He)
5.24 ppmv (0.000524%)
Methane (CH4)
1.79 ppmv (0.000179%)
Krypton (Kr)
1.14 ppmv (0.000114%)
Hydrogen (H2)
0.55 ppmv (0.000055%)
Nitrous oxide (N2O)
0.325 ppmv (0.0000325%)
Carbon monoxide (CO)
0.1 ppmv (0.00001%)
Xenon (Xe)
0.09 ppmv (9×10−6%) (0.000009%)
Ozone (O3)
0.0 to 0.07 ppmv (0 to 7×10−6%)
Nitrogen dioxide (NO2)
0.02 ppmv (2×10−6%) (0.000002%)
Iodine (I2)
0.01 ppmv (1×10−6%) (0.000001%)
Ammonia (NH3)
trace
Not included in above dry atmosphere:
Water vapor (H2O)
~0.40% over full atmosphere, typically 1%–4% at surface

That clears it up.