Atmospheric Structure and Composition

Atmosphere: The thin envelope of gases surrounding the earth Highly compressible Density decreases rapidly with height Air: A mechanical mixture of gases and aerosols Definitions

Vertical Structure of Atmosphere u Troposphere (surface to 8-20 km) Upper boundary varies from about 8 km (poles in winter) to about 20 km (tropics) Weather and climate layer Most of atmosphere’s mass; all of its water

Vertical Structure of Atmosphere u Troposphere (surface to about 8-20 km) Upper boundary varies from about 8 km (poles in winter) to about 20 km (tropics) Weather and climate layer Most of atmosphere’s mass; all of its water u Stratosphere (8-20 km up to about 50 km) Ozone (O 3 ) Layer Temperature inversion

Vertical Structure (ctd.) u Mesosphere (50-80 km) –Temperature decreases with height. Why? u Thermosphere (80-? km) –Temperature inversion. Why?

Vertical Structure (ctd.) u Homosphere vs. Heterosphere

Vertical Structure (ctd.) u Homosphere vs. Heterosphere u Transition zones between layers –Tropopause –Stratopause –Mesopause

Defining Layers by Function – the Ozonosphere u Roughly corresponds to the stratosphere u How does the ozone layer work? u Why is there a “hole” in the ozone layer? –Why no “hole” where the pollution is produced?

Defining Layers by Function – the Ionosphere u Upper mesosphere + thermosphere u Produces the aurora borealis and aurora australis u D Layer – absorbs AM radio waves; disappears at night u E Layer – weakens at night u F Layer – reflects AM radio waves

Composition of the Air u Uniform gases Nitrogen (N 2 ) 78%, (O 2 ) 21%, Argon (Ar) 1%, trace gases (Neon, Helium, Methane (CH 4 ), etc.) u Variable gases Water Vapor (H 2 O v ), O 3, CO 2

Composition (ctd.) u Aerosols Solid: Ice/salt crystals, soil particles, volcanic dust Condensation nuclei Liquid: Water droplets (cloud, fog)

Origin of the Atmosphere u Volcanoes release H 2, CO 2, H 2 O v, N 2, NH 3, CH 4 No O 2 or O 3, so no land organisms! u One-celled aquatic organisms release CO 2 to atmosphere when breaking down food through fermentation u Simple aquatic plants took in CO 2 and released O 2 to atmosphere via photosynthesis O 3 formed from the O 2

Origin of Atmosphere (ctd) u CO 2 gets stored in shells and decaying plants u N 2 builds up in atmosphere