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Carbondioxideisanotherimportantvariablecomponentofthe
atmosphere.Itisaproductofcombustionofenergyresources,respiration
oflivingorganismsandthedecompositionoforganicmatter.Carbondioxide
allowstheshort-wavesolarradiationtoentertheatmospherewhileblocking
thelong-wave(infrared)radiationrefectedfromtheplanet)ssurface,thus
contributingtoelevatingthetemperatureonEarth.
Ozoneisaprotectiveshieldabsorbingtheultravioletradiation,whichis
consideredamongelementsoftheatmospherecriticaltothebiologicallife
onEarth.Itsgreatestconcentrationoccursatanaltitudeof20-30kmabove
Earth)ssurface.Itisproducedinthephotochemicalreactioncatalysedby
ultraviolet(UV)radiation.UnderUVradiation,molecularoxygendissociates
intoindividualatomsandtheirsubsequentcollisionswithoxygenmolecules
leadtothecreationofozone.
Aerosolsrepresentthelastgroupofairadmixtures.Thisgroupincludes
liquidorsolidparticlessuspendedintheatmosphericair,suchasplantpollen,
bacteria,ash(volcanicandindustrial)orsalt.Thesesubstancesoccuronlyin
theboundarylayerofEarth.
Earth)satmosphereisdividedaccordingtoseveralcriteria,presentedin
Figure1.ThesurfaceofEarthisthelowerboundaryoftheatmosphere,while
theupperboundaryhasyetescapedaclear-cutdemarcation.Nevertheless,
conventionally,theupperboundaryofEarth)satmosphereisthoughtto
extendtothealtitudeofca2000-3000km,sinceitisinthatrangethatthe
gasesexhibitdensitycharacteristicofthegasesoftheinterplanetarymedium.
Accordingtothedivisionbasedonthechemicalcompositionofair,Earth)s
atmosphereisseparatedintohomosphereandheterosphere.Homosphereis
thelowestpartofEarth)satmosphereextendingfromitssurfaceandreaching
theheightofapprox.100kmaboveitslevel.Itscharacteristicfeatureis
homogeneouschemicalcomposition,maintainedbyverticalcurrentsand
turbulenceintheatmosphere.Heterosphereconstitutestheupperpartofthe
atmosphere,characterisedbynon-homogeneousaircomposition,resulting
fromdiffusivegasseparationandthedissociationofmoleculesintoatomsby
ultravioletradiation.
Consideringairdensity,theatmosphereofEarthisdividedintofourlayers:
-airspace-extendsfromground(GND)totheheightof65km.Inits
lowerlimits,theairdensityissufficienttoenabletheaerodynamiclifttoact
ontheaircraft,whichallowsstandardaircrafttooperatewithintherangeof
GNDto35km;
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