The atmosphere is divided into a number of layers, each with its own set of conditions. The constituents of the atmosphere are the same throughout.
tropopause. Boundary between the troposphere and stratosphere.
stratosphere. (10-50km). Nacreous clouds and most of the ozone. Temperature increases slowly with height.
mesosphere. (50-80km). Noctilucent clouds. Temperature decreases with height.
ionosphere. (80-400km). Radio reflective layer of electrically charged nitrogen and oxygen particles.
thermosphere. (80-500km). Temperature increases with height.
exosphere. (>500km). Beyond the atmosphere.
invariables. Nitrogen 78%, oxygen 21%, argon 1%. Less than 1%: neon, helium, methane, krypton, hydrogen, nitrous-oxide, xenon.
variables. Water vapour 0.0 to 0.7%, carbon-dioxide 0.01 to 0.1% (average 0.034%), ozone up to 0.000007%.
contaminants. Sulphur-dioxide <0.0001%, nitrogen-dioxide <0.000002%, traces of ammonia and carbon-monoxide.