Atmospheric Structure Atmospheric Structure and Compositionand 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

DefinitionsDefinitions

Vertical Structure of AtmosphereVertical Structure of Atmosphere

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 AtmosphereVertical Structure of Atmosphere 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 layerMost of atmosphere’s mass; all of its

water

Stratosphere (8-20 km up to about 50 km)

Ozone (O3) LayerTemperature inversion

Vertical Structure (ctd.)Vertical Structure (ctd.)

Mesosphere (50-80 km)– Temperature decreases with height. Why?

Thermosphere (80-? km)– Temperature inversion. Why?

Vertical Structure (ctd.)Vertical Structure (ctd.) Homosphere vs. Heterosphere

Vertical Structure (ctd.)Vertical Structure (ctd.) Homosphere vs. Heterosphere

Transition zones between layers– Tropopause– Stratopause– Mesopause

Defining Layers by Function – Defining Layers by Function – the Ozonospherethe Ozonosphere

Roughly corresponds to the stratosphere

How does the ozone layer work?

Why is there a “hole” in the ozone layer?

– Why no “hole” where the pollution is produced?

Defining Layers by Function – Defining Layers by Function – the Ionospherethe Ionosphere

Upper mesosphere + thermosphere Produces the aurora borealis and aurora

australis D Layer – absorbs AM radio waves;

disappears at night E Layer – weakens at night F Layer – reflects AM radio waves

Composition of the AirComposition of the Air Uniform gases

Nitrogen (N2) 78%, (O2) 21%,

Argon (Ar) 1%, trace gases (Neon, Helium, Methane (CH4), etc.)

Variable gases

Water Vapor (H2Ov), O3, CO2

Composition (ctd.)Composition (ctd.) Aerosols

Solid: Ice/salt crystals, soil particles, volcanic dust

Condensation nuclei

Liquid: Water droplets (cloud, fog)

Origin of the AtmosphereOrigin of the Atmosphere Volcanoes release H2, CO2, H2Ov, N2, NH3, CH4

No O2 or O3, so no land organisms!

One-celled aquatic organisms release CO2 to atmosphere when breaking down food through fermentation

Simple aquatic plants took in CO2 and released O2 to atmosphere via photosynthesis

O3 formed from the O2

Origin of Atmosphere (ctd)Origin of Atmosphere (ctd)

CO2 gets stored in shells and decaying plants

N2 builds up in atmosphere