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Composition of the atmosphere

Composition of the Atmosphere near the Earth's Surface
Permanent Gases Variable Gases
Gas Name Chemical
(by Volume)
Dry Air
(and Particles)
Symbol Percent
(by Volume)
Parts per
Million (ppm)*
Nitrogen N2 78.08 Water Vapor H2O 0 to 4  
Oxygen O2 20.95 Carbon Dioxide CO2 0.0393 393
Argon Ar 0.93 Methane CH4 0.00017 1.7
Neon Ne 0.0018 Nitrous Oxide N2O 0.00003 0.3
Helium He 0.0005 Ozone O3 0.000004 0.04
Hydrogen H2 0.00005 Particles (dust, soot, etc.)   0.00001 0.01-0.15
Xenon Xe 0.000009 Chlorofluorocarbons (CFCs)   0.00000002 0.0002
*For CO2, 393 parts per million means that out of every million air molecules, 393 are CO2 molecules.

Major Components of the Atmosphere

The Atmosphere is mostly composed of Nitrogen and Oxygen. These make up 99% of the volume of "dry air". In this context "dry air" refers to all gases, except water vapor.

Removed from atmosphere by biological processes that involve soil bacteria. Returned to the atmosphere through the decaying of plant and animal matter.
Removed from atmosphere by when organic matter decays, combines with other substances, or is taken in during breathing. Is added to the atmosphere through photosynthesis by plants.

Some Important Trace Components of the Atmosphere

Water Vapor:
Carbon Dioxide:
Nitrous Oxide:

Aerosols are tiny solid or liquid particles that are suspended in the air. Most aerosols are microscopic and too small to see individually without a microscope. Aerosols include things like dust, pollen, smoke, and even cloud droplets. When there are high concentrations of aerosols in the air, they do affect the propagation of light, and thus affect visibility. Examples are the visible thick smoke that comes off fires and normal clouds.

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