The Atmosphere and the Weather

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Composition of the atmosphere

Composition of the Atmosphere near the Earth's Surface
Permanent Gases Variable Gases
Gas Name Chemical
Formula
Percent
(by Volume)
Dry Air
Gas
(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 0.0383 383
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, 383 parts per million means that out of every million air molecules, 383 are CO2 molecules.

The Atmosphere is mostly composed of Nitrogen and Oxygen (99% of the volume of dry atmosphere).

Nitrogen:
Removed from atmosphere by biological processes that involve soil bacteria. Returned to the atmosphere through the decaying of plant and animal matter.
Oxygen:
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.
Water Vapor:
Varies greatly from place to place, and from time to time.
Extremely important gas in our atmosphere because:
Carbon Dioxide:
Natural component of the atmosphere.
Enters the atmosphere through the decay of vegetation, volcanic eruptions, respiration, burning of fossil fuels, and from deforestation. It is removed from the atmosphere by photosynthesis, and the oceans.
Has increased by over 25% in the last three hundred years.
Methane:
Very strong greenhouse gas.
Since 1750, methane concentrations have increased by more than 140%.
The main sources are the breakdown of plant material in rice paddies, domestic grazing animals (biological reactions in their stomach), biological activities of termites.
Nitrous Oxide:
Forms in the soil by bacterial processes and is destroy by ultraviolet light from the sun.
Average concentration of this greenhouse gas is now increasing at a rate of 0.2-0.3% per year
Ozone:
Near the surface and around cities is the primary ingredient of photochemical smog, which is toxic to living organisms.
Most of it is found in the middle atmosphere (the stratosphere) where it forms the ozone layer which protects plants, animals, and humans from the sun's harmfull ultraviolet radiation.

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