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== air ==


Mixture of gases forming Earth's [[atmosphere]], consisting of nitrogen (∼78%), oxygen (∼21%), [[water vapor]], and other [[trace gas|trace gases]] such as carbon dioxide, helium, argon, [[ozone]], or various pollutants.<br/>


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The concentration of water vapor is very variable, being a strong function of [[temperature]] and, hence, [[altitude]] in the atmosphere. [[dry air|Dry air]] is referred to as air from which measurable amounts of water vapor have been physically removed. Pure, dry air has a [[density]] of 1.293 kg m<sup>&minus;3</sup> at a temperature of 273 K and a [[pressure]] of 101.325 kPa. Apart from the variability of water vapor, the composition of air is essentially constant to an altitude of at least 50 km and is presently approximated as follows.<br /><br />
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== air ==
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<div class="definition"><div class="short_definition">Mixture of gases forming the earth's [[atmosphere]], consisting of nitrogen (&sim;78 percent), oxygen  (&sim;21 percent), [[water vapor]], and other [[trace gas|trace gases]] such as carbon dioxide, helium, argon, [[ozone]],  or various pollutants.</div><br/> <div class="paragraph">The concentration of water vapor is very variable, being a strong function of [[temperature]] and,  hence, [[altitude]] in the atmosphere. [[dry air|Dry air]] is referred to as air from which measurable amounts  of water vapor have been physically removed. Pure, dry air has a [[density]] of 1.293 kg m<sup>-3</sup> at a  temperature of 273 K and a [[pressure]] of 101.325 kPa. Apart from the variability of water vapor,  the composition of air is essentially constant to an altitude of at least 50 km and is presently  approximated as follows.[[File:ams2001glos-At1.gif|link=|center|ams2001glos-At1]]The concentration of ozone is variable, between 10 and 0.1 parts per million. Carbon dioxide,  methane, and nitrous oxide have all been increasing since the beginning of the industrial age.</div><br/> </div>
[[File:Air_table_revised.PNG|link=|center|revised air table]]<br />
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The concentration of ozone is variable, between approximately 10 and 0.01 ppm. Carbon dioxide, methane, and nitrous oxide have all been increasing since the beginning of the industrial age. Carbon dioxide and methane concentrations vary by season and location. <br/>
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[[Category:Terms_A]]
<p>''Term revised 26 June 2017.''</p>

Latest revision as of 21:29, 27 March 2024

air[edit | edit source]

Mixture of gases forming Earth's atmosphere, consisting of nitrogen (∼78%), oxygen (∼21%), water vapor, and other trace gases such as carbon dioxide, helium, argon, ozone, or various pollutants.

The concentration of water vapor is very variable, being a strong function of temperature and, hence, altitude in the atmosphere. Dry air is referred to as air from which measurable amounts of water vapor have been physically removed. Pure, dry air has a density of 1.293 kg m−3 at a temperature of 273 K and a pressure of 101.325 kPa. Apart from the variability of water vapor, the composition of air is essentially constant to an altitude of at least 50 km and is presently approximated as follows.

revised air table


The concentration of ozone is variable, between approximately 10 and 0.01 ppm. Carbon dioxide, methane, and nitrous oxide have all been increasing since the beginning of the industrial age. Carbon dioxide and methane concentrations vary by season and location.

Term revised 26 June 2017.

Colorless gas, formula CO2, molecular weight 44; the fourth most abundant gas in dry air. The end product of the combustion or oxidation of organic material, including fossil fuels, CO2 is a very strong greenhouse gas and has very important radiative effects.
Carbon dioxide is soluble in water, and the atmospheric concentration is buffered by dissolution in seawater. Carbon dioxide is taken up by the biosphere during photosynthesis, and large amounts of carbon can be stored in decaying organic matter.

A division of the year according to some regularly recurrent phenomena, usually astronomical or climatic.

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