8/2/2019 V.ROSHAN

1/18

8/2/2019 V.ROSHAN

2/18

8/2/2019 V.ROSHAN

3/18

TOPIC:TOPIC:

COMPOSITION OF AIRCOMPOSITION OF AIR

8/2/2019 V.ROSHAN

4/18

The atmosphere of Earth is a layer ofThe atmosphere of Earth is a layer ofgasesgases

surrounding the planetsurrounding the planetEarthEarth that is retainedthat is retained

by Earth'sby Earth'sgravitygravity. The. The atmosphereatmosphereprotectsprotectslife on Earthlife on Earth by absorbingby absorbingultravioletultraviolet solarsolar

radiationradiation

, warming the surface through heat, warming the surface through heat

retention (retention (greenhouse effectgreenhouse effect

), and reducing), and reducing

temperaturetemperature extremes betweenextremes between dayday andandnightnight(the(the diurnal temperature variationdiurnal temperature variation

).).

8/2/2019 V.ROSHAN

5/18

Atmospheric stratificationAtmospheric stratification describes thedescribes thestructure of the atmosphere, dividing it intostructure of the atmosphere, dividing it intodistinct layers, each with specificdistinct layers, each with specific

characteristics such as temperature orcharacteristics such as temperature orcomposition. The atmosphere has a mass ofcomposition. The atmosphere has a mass ofabout 5about 51018 kg, three quarters of which is1018 kg, three quarters of which iswithin about 11within about 11 km (6.8km (6.8 mi; 36,000 ft) of themi; 36,000 ft) of the

surface. The atmosphere becomes thinnersurface. The atmosphere becomes thinnerand thinner with increasingand thinner with increasingaltitudealtitude

, with no, with nodefinitedefinite

8/2/2019 V.ROSHAN

6/18

8/2/2019 V.ROSHAN

7/18

Blue light is scattered moreBlue light is scattered more than other wavelengthsthan other wavelengths

by the gases in the atmosphere, giving the Earth aby the gases in the atmosphere, giving the Earth a

blueblue halohalo when seen from space.when seen from space.

8/2/2019 V.ROSHAN

8/18

Limb view, of the Earth's atmosphere. Colours roughlyLimb view, of the Earth's atmosphere. Colours roughlydenote the layers of the atmospheredenote the layers of the atmosphere..

The atmosphere of Earth is a layer ofThe atmosphere of Earth is a layer ofgasesgasessurrounding thesurrounding theplanetplanetEarthEarth that is retained by Air is the name given tothat is retained by Air is the name given to

atmosphereatmosphere used inused in breathingbreathingandandphotosynthesisphotosynthesis. Dry air. Dry aircontains roughly (by volume) 78.09%contains roughly (by volume) 78.09% nitrogennitrogen, 20.95%, 20.95%oxygenoxygen, 0.93%, 0.93% argonargon, 0.039%, 0.039% carbon dioxidecarbon dioxide, and small, and smallamounts of other gases. Air also contains a variable amountamounts of other gases. Air also contains a variable amountofofwater vaporwater vapor, on average around 1%. While air content, on average around 1%. While air content

andandatmospheric pressureatmospheric pressure varies at different layers, airvaries at different layers, airsuitable for the survival ofsuitable for the survival ofterrestrial plantsterrestrial plants

8/2/2019 V.ROSHAN

9/18

terrestrial animalsterrestrial animals is currently only known tois currently only known to

be found in Earth'sbe found in Earth's tropospheretroposphere and artificialand artificial

atmospheres. Compositionatmospheres. Composition

8/2/2019 V.ROSHAN

10/18

n

8/2/2019 V.ROSHAN

11/18

artificialartificial atmospheres. Compositionatmospheres. Composition

Mean atmospheric water vapour

8/2/2019 V.ROSHAN

12/18

Structure of the atmosphereStructure of the atmosphere

Principal layersPrincipal layers

n general, air pressure and density decrease in then general, air pressure and density decrease in the

atmosphere as height increases. However,atmosphere as height increases. However,temperature has a more complicated profile withtemperature has a more complicated profile withaltitude. Because the general pattern of this profilealtitude. Because the general pattern of this profileis constant and recognizable through means such asis constant and recognizable through means such asballoon soundingsballoon soundings, temperature provides a useful, temperature provides a useful

metric to distinguish between atmospheric layers. Inmetric to distinguish between atmospheric layers. Inthis way, Earth's atmosphere can be divided intothis way, Earth's atmosphere can be divided intofive main layers. From highest to lowest, thesefive main layers. From highest to lowest, theselayers are:layers are:

8/2/2019 V.ROSHAN

13/18

Physical propertiesPhysical properties

The average atmospheric pressure atThe average atmospheric pressure atsea levelsea levelis about 1is about 1atmosphere (atm) = 101.3 kPa (kilopascals) = 14.7 psiatmosphere (atm) = 101.3 kPa (kilopascals) = 14.7 psi(pounds per square inch) = 760 torr = 29.92(pounds per square inch) = 760 torr = 29.92 inches ofinches of

mercury (symbol Hg). Total atmospheric mass ismercury (symbol Hg). Total atmospheric mass is5.14805.14801018 kg (1.1351018 kg (1.1351019 lb),1019 lb),[14][14]about 2.5% less thanabout 2.5% less thanwould be inferred from the average sea level pressure andwould be inferred from the average sea level pressure andthe Earth's area of 51007.2 megahectares, this portion beingthe Earth's area of 51007.2 megahectares, this portion beingdisplaced by the Earth's mountainous terrain. Atmosphericdisplaced by the Earth's mountainous terrain. Atmospheric

pressure is the total weight of the air above unit area at thepressure is the total weight of the air above unit area at thepoint where the pressure is measured. Thus air pressurepoint where the pressure is measured. Thus air pressurevaries with location andvaries with location andweatherweather..

8/2/2019 V.ROSHAN

14/18

If atmospheric density were to remain constant with heightIf atmospheric density were to remain constant with heightthe atmosphere would terminate abruptly at 8.50the atmosphere would terminate abruptly at 8.50 km (27,900km (27,900

ft). Instead, density decreases with height, dropping by 50%ft). Instead, density decreases with height, dropping by 50%at an altitude of about 5.6at an altitude of about 5.6 km (18,000km (18,000 ft). As a result theft). As a result the

pressure decrease is approximately exponential with height,pressure decrease is approximately exponential with height,so that pressure decreases by a factor of two approximatelyso that pressure decreases by a factor of two approximatelyevery 5.6every 5.6 km (18,000km (18,000 ft) and by a factor of e = 2.718ft) and by a factor of e = 2.718approximately every 7.64approximately every 7.64 km (25,100 ft), the latter being thekm (25,100 ft), the latter being theaverageaveragescale heightscale heightof Earth's atmosphere below 70of Earth's atmosphere below 70 kmkm(43(43 mi; 230,000 ft). However, because of changes inmi; 230,000 ft). However, because of changes in

temperature, average molecular weight, and gravitytemperature, average molecular weight, and gravitythroughout the atmospheric column, the dependence ofthroughout the atmospheric column, the dependence ofatmospheric pressure on altitude is modeled by separateatmospheric pressure on altitude is modeled by separateequations for each of the layers listed above.equations for each of the layers listed above.

8/2/2019 V.ROSHAN

15/18

..Even in the exosphere, the atmosphere isEven in the exosphere, the atmosphere is

still present. This can be seen by the effects ofstill present. This can be seen by the effects of

atmospheric dragatmospheric dragononsatellitessatellites..

In summary, the equations of pressure byIn summary, the equations of pressure by

altitude in the above references can be usedaltitude in the above references can be used

directly to estimate atmospheric thickness.directly to estimate atmospheric thickness.

However, the following published data areHowever, the following published data are

given for referencegiven for reference

8/2/2019 V.ROSHAN

16/18

8/2/2019 V.ROSHAN

17/18

Temperature and mass density against altitude from theTemperature and mass density against altitude from theNRLMSISENRLMSISE--0000 standard atmospherestandard atmosphere model (the eight dottedmodel (the eight dottedlines in each "decade" are at the eight cubes 8, 27, 64, ...,lines in each "decade" are at the eight cubes 8, 27, 64, ...,729)729)

Main article:Main article:Density of airDensity of airThe density of air at sea level isThe density of air at sea level isabout 1.2about 1.2 kg/m3 (1.2 g/L). Density is not measured directlykg/m3 (1.2 g/L). Density is not measured directlybut is calculated from measurements of temperature,but is calculated from measurements of temperature,

pressure and humidity using the equation of state for air (apressure and humidity using the equation of state for air (aform of theform of the ideal gas lawideal gas law). Atmospheric density decreases as). Atmospheric density decreases as

the altitude increases. This variation can be approximatelythe altitude increases. This variation can be approximatelymodeled using themodeled using the barometric formulabarometric formula. More sophisticated. More sophisticatedmodels are used to predict orbitalmodels are used to predict orbital decay of satellites.decay of satellites.

8/2/2019 V.ROSHAN

18/18