Atmosphere of Earth

Monday, January 11, 2010

From Wikipedia, the free encyclopedia

(Redirected from Air)

"Air" redirects here. For other uses, see Air (disambiguation).

Blue light is scattered more than other wavelengths by the gases in the atmosphere, giving the Earth a blue halo when seen from space

The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention (greenhouse effect), and reducing temperature extremes between day and night. Dry air contains roughly (by volume) 78% nitrogen, 21% oxygen, 0.93% argon, 0.038% carbon dioxide, and small amounts of other gases. Air also contains a variable amount of water vapor, on average around 1%.

The atmosphere has a mass of about five quintillion (5x10¹⁸) kg, three quarters of which is within about 11 km (6.8 mi; 36,000 ft) of the surface. The atmosphere becomes thinner and thinner with increasing altitude, with no definite boundary between the atmosphere and outer space. An altitude of 120 km (75 mi) is where atmospheric effects become noticeable during atmospheric reentry of spacecraft. The Kármán line, at 100 km (62 mi), also is often regarded as the boundary between atmosphere and outer space.

Composition

Main article: Atmospheric chemistry

Composition of Earth's atmosphere as at Dec. 1987. The lower pie represents the trace gases which together compose 0.038% of the atmosphere. Values normalized for illustration.

Mean atmospheric water vapor

Air is mainly composed of nitrogen, oxygen, and argon, which together constitute the "major gases" of the atmosphere. The remaining gases often are referred to as "trace gases,"^[1] among which are the greenhouse gases such as water vapor, carbon dioxide, methane, nitrous oxide, and ozone. Filtered air includes trace amounts of many other chemical compounds. Many natural substances may be present in tiny amounts in an unfiltered air sample, including dust, pollen and spores, sea spray, volcanic ash, and meteoroids. Various industrial pollutants also may be present, such as chlorine (elementary or in compounds), fluorine (in compounds), elemental mercury, and sulfur (in compounds such as sulfur dioxide [SO₂]).

**Composition of dry atmosphere, by volume**^[2]
Gas	Volume
ppmv: parts per million by volume (note: volume fraction is equal to mole fraction for ideal gas only, see Gas volume#Partial volume)
Nitrogen (N₂)	780,840 ppmv (78.084%)
Oxygen (O₂)	209,460 ppmv (20.946%)
Argon (Ar)	9,340 ppmv (0.9340%)
Carbon dioxide (CO₂)	387 ppmv (0.0387%)
Neon (Ne)	18.18 ppmv (0.001818%)
Helium (He)	5.24 ppmv (0.000524%)
Methane (CH₄)	1.79 ppmv (0.000179%)
Krypton (Kr)	1.14 ppmv (0.000114%)
Hydrogen (H₂)	0.55 ppmv (0.000055%)
Nitrous oxide (N₂O)	0.3 ppmv (0.00003%)
Xenon (Xe)	0.09 ppmv (9x10⁻⁶%)
Ozone (O₃)	0.0 to 0.07 ppmv (0% to 7x10⁻⁶%)
Nitrogen dioxide (NO₂)	0.02 ppmv (2x10⁻⁶%)
Iodine (I)	0.01 ppmv (1x10⁻⁶%)
Carbon monoxide (CO)	0.1 ppmv
Ammonia (NH₃)	trace
Not included in above dry atmosphere:
Water vapor (H₂O)	~0.40% over full atmosphere, typically 1%-4% at surface

Dafi's Blog

Ancor ( ajang coret-coret )