Earth's atmosphere

Earth's atmosphere is the layer of gases surrounding the planet Earth and retained by the Earth's gravity. It contains roughly 78% nitrogen and 21% oxygen, with trace amounts of other gases. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation and reducing temperature extremes between day and night.

Composition

Percent Composition of Dry Atmosphere,by volume - ppmv: parts per million by volume

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Gasper NASA

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Nitrogen (N2)78.084%

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Oxygen (O2)20.946%

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Argon (Ar)0.9340%

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Carbon dioxide (CO2)365 ppmv

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Neon (Ne)18.18 ppmv

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Helium (He)5.24 ppmv

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Methane (CH4)1.745 ppmv

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Krypton (Kr)1.14 ppmv

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Hydrogen (H2)0.55 ppmv

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Not included in above composition of dry atmosphere:

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Water vaporHighly variable;typically makes up about 1%

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Carbon dioxide and methane updated (to 1998) by IPCC TAR table 6.1 http://www.grida.no/climate/ipcc_tar/wg1/221.htm

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Minor components of air not listed above include: nitrous oxide (0.5 ppmv), xenon (0.09 ppmv), ozone (0.0 to 0.07 ppmv, 0.0 to 0.02 ppmv in winter), nitrogen dioxide (0.02 ppmv), iodine (0.01 ppmv), carbon monoxide (0.0 to trace), and ammonia (0.0 to trace).

Related Topics:
Nitrous oxide - Xenon - Ozone - Winter - Nitrogen dioxide - Iodine - Carbon monoxide - Ammonia

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The mean molecular mass of air is 28.97 g/mol.

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Heterosphere

Below an altitude of about 100 km, the Earth's atmosphere has a more-or-less uniform composition (apart from water vapor) as described above. However, above about 100 km, the Earth's atmosphere begins to have a composition which varies with altitude. This is essentially because, in the absence of mixing, the density of a gas falls off exponentially with increasing altitude, but at a rate which depends on the molecular mass. Thus higher mass constituents, such as oxygen and nitrogen, fall off more quickly than lighter constituents such as helium, molecular hydrogen, and atomic hydrogen. Thus there is a layer, called the heterosphere, in which the earth's atmosphere has varying composition. As the altitude increases, the atmosphere is dominated successively by helium, molecular hydrogen, and atomic hydrogen. The precise altitude of the heterosphere and the layers it contains varies significantly with temperature.http://www.oma.be/BIRA-IASB/Public/Research/Thermo/Thermotxt.en.html

Related Topics:
Molecular mass - Helium - Hydrogen

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