Composition of Atmosphere Near the Earth's Surface by Number of Molecules
Type

Component

Concentration*
Permanent
Gases		 N2 (Molecular Nitrogen) 78.08%
O2 (Molecular Oxygen) 20.95%
Ar (Atomic Argon) 0.93%
Ne (Atomic Neon) 0.0018%
He (Atomic Helium) 0.0005%
H2 (Molecular Hydrogen) 0.00006%
Xe (Atomic Xenon) 0.000009%
Variable Gases H2O (Water Vapor)§ 0 to 4%
CO2 (Carbon Dioxide) 374 ppm
CH4 (Methane) 1.7 ppm
N2O (Nitrous Oxide) 0.3 ppm
O3 (Ozone) 0.04 ppm♦
Chlorofluorocarbons (CFCs)Ä 0.0002 ppm
Particulates© Water, Ice, Dust, Smoke, Pollen, Salt, Industrial Emissions, . . . 0.01 to 0.15 ppm

  *% is mass percentage, whereas ppm means that out of every million air molecules, the indicated number of them are of
     that component.
  §Components in red contribute to the greenhouse effect.
  ♦Stratospheric values of ozone at altitudes between 11 km and 50 km range from ~5 to ~12 ppm.
  ÄCFCs cause the destruction of stratospheric ozone.
  ©Particulates (aka "aerosols") are highly visible.  These, both natural and man-made, are extremely variable.