parts of atmosphere - 4 regions  

• troposphere - where people live, goes to about 12 km
• stratosphere - reaches 50 km
• mesosphere - reaches 85 km
• thermosphere - past mesosphere
• temperature change opposite in successive region
• pressure change remains constant (decreases as elevation increases)

atmospheric composition - made up of mostly nitrogen, oxygen  

• nitrogen = 78%
• oxygen = 21%
• argon, carbon dioxide, water vapor = next most commonly found gases
• oxygen reacts more than nitrogen (triple bond)
• photodissociation - photons from the sun breaking chemical bonds
  • O2 + energy >> 2O
  • mostly dissociated at very high elevations
• photoionization - loss of electron due to molecule absorbing radiation
• ozone (O3) forms from photodissociated oxygen and oxygen molecules
  • most ozone found in stratosphere
• chlorofluorocarbons (CFC) - depletes the ozone layer
  • harmless in lower atmosphere
  • reaches higher atmosphere >> more radiation >> more photodissociation
  • chloride w/ oxygen forms chlorine monoxide

troposphere composition - like atmosphere, mostly nitrogen/oxygen  

• acid rain - due to nitrogen oxides in air
  • NOx from fossil fuel burning
  • kills animals, corrodes metals/stone
• carbon monoxide - along w/ cyanide, bonds to hemoglobin better than oxygen
• photochemical smog - stagnant air mass due to nitric oxide
  • ozone acts as pollutant in lower atmosphere
• carbon dioxide/methane - contributes to greenhouse effect