The Atmosphere and the Weather

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	0.0372	372
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, 372 parts per million means that out of every million air molecules, 372 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:

• Forms into liquid and solid cloud particles that grow in size and fall to earth as precipitation
• Redistributes heat energy on earth and is important to the formation of storms
• Is a strong greenhouse gas that warms the earth's surface and its atmosphere

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 upper atmosphere (the stratosphere) where it forms the ozone layer which protects plants, animals, and humans from the sun's harmfull ultraviolet radiation.