The Structure and Composition of the Atmosphere

• Composition of the Atmosphere:

  A) Oxygen

  B) argon

  C) CO2

  D) Nitrogen

  
• Number of years gas stays in atmosphere:

  • Carbon Dioxide - 200 years
  • Methane - 12-17 years
  • CFCs - 1000 years
  • Nitrous Oxides - 114 years
• Atmosphere - a layer of gases held to the Earth by gravitational force

  • gravity and compression mean that 50% of the atmosphere lies within 5.6km of the Earth’s surface
• Earth didn’t originally have an atmosphere but as the planet cooled, gases were released and an atmosphere began to form
• Atmosphere is composed of:

  • nitrogen (mostly the product of volcanic eruptions)
  • oxygen
  • argon (inert or noble gas)
  • carbon dioxide (cycled through photosynthesis, respiration and burning fossil fuels)
  • ozone
  • very small traces of inert gases like krypton
  • aerosols or solid particies (minute particles of dust like salt, fine sand and volcanic ash)
  • water vapour
• Carbon dioxide and ozone as referred to as variable gases because their quantity can change as a result of processes e.g. evaporation, transpiration, pollution and seasonal change
• Noble gas - a gas that reacts with other elements because it is stable, previously referred to as inert gases
• Aerosols - sprays containing fine particles and/or droplets that become suspended in the atmosphere
• Natural balances of gases in the atmosphere is maintained by various cycles eg. nitrogen cycle and carbon cycle

  • human activities can alter the composition in many ways
  • CO2 is added by burning fossil fuels and deforestation
  • growing rice and keeping cattle increases methane levels
  • can reduce some gases by afforestation or releasing ozone destroying chlorofluorocarbons (CFCs)
• • Composition of the atmosphere

  A) 78.09

  B) 20.95

  C) growth of plants

  D) photosynthesis

  E) respiration

  F) 0.2-4

  G) 0.03

  H) 0.00006

  I) precipitation

  J) greenhouse gases

  K) existence of life

  L) photosynthesis

  M) primary

  N) producers

  O) other life

  P) greenhouse gas

  Q) UV radiation

  R) 0.93

  S) Trace

  T) inert atmosphere

  U) oxygen

  V) gases

  W) trace

  X) absorbs

  Y) reflects

  Z) short-wave radiation

  [) condenses

  \) droplets

  ]) ice

  ^) cloud formation

  _) trace

  `) smog

  a) acid rain

  b) ozone depletion

  c) enhanced greenhouse effect

  
• Atmosphere can be divided into four layers

  A) troposphere

  B) tropopause

  C) height varies

  D) stratosphere

  E) stratopause

  F) mesosphere

  G) mesopause

  H) thermosphere

  
• Troposphere

  • the warming effect of the Earth’s surface through conduction and convection decreases as altitude increases
  • strength of gravitational pull declines with altitude and pressure declines too
  • wind speeds increase with height
  • the top of this layer is marked by tropopause - temperatures remain fairly constant, boundary occurs at aboutt 8km at the poles and 17km in the tropics
  • marks the upper limit to the Earth’s weather and climate
• Stratosphere

  • layer extends to nearly 50km above the Earth’s surface
  • pressure continues to fall
  • temperature inversion - temperatures increase steadily with height and is caused by the concentration of ozone, which absorbs the incoming UV radiation from the sun
  • acts as a shield against incoming meteorites which burn out when they enter the gravitational field
  • stratopause - upper limit of stratosphere
• Thermosphere

  • layer is 80-1000km in height
  • temperatures rise rapidly to as high as 1500C because of absorption of UV radiation by atomic oxygen
  • thermopause - marks the upper limit of this layer
• Mesosphere

  • layer is 50-80km in height
  • pressure continues to decrease
  • temperatures fall rapidly to below -80C because there is no water vapour, dust or ozone to absorb the incoming short-wave radiation
  • winds can reach up to speeds of 3000 kmh^-1
  • mesopause - marks the upper limit of this layer
• Natural greenhouse effect - a process that helps keep the Earth’s surface and atmosphere warm
• Natural greenhouse effect

  A) radiation

  B) sun

  C) radiation

  D) passes

  E) green

  F) houses

  G) gases

  H) absorbs radiation

  I) heats

  J) emits radiation

  K) greenhouse

  L) gases

  M) outgoing radiation

  N) heats

  
• The earth receives incoming short-wave radiation from the sun

  • half of this radiation is absorbed by the earth’s surface - around 20% is absorbed by the atmosphere and 30% is reflected by clouds and the Earth’s surface back into space
• As the earth’s surface warms, outgoing long-wave radiation or infrared radiation is emitted back into the atmosphere

  • greenhouse gases absorb some of this radiation and deflect it back to the earth’s surface
  • process maintains the Earth’s temperature at around 33C warmer than it would
• Greenhouse gases make up a small proportion of the atmosphere but act like a blanket trapping the radiation

  • the greater the concentration of greenhouse gases, the more effectively they return radiation back to the Earth’s surface
• Main greenhouse gases are:

  • Carbon dioxide
  • Methane
  • nitrous oxides
  • CFCs (gases containing fluorine, chlorine and carbon) are artificial greenhouse gases
  • ozone
• • Each greenhouse gase stay in the atmosphere for differing amounts of time

  A) 65

  B) 200

  C) 17

  D) 12

  E) 12

  F) 1000

  G) 6

  H) 114