Effects of Greenhouse Gases

• The Sun emits energy in the form of radiation that enters the Earth’s atmosphere

  • Some thermal energy is reflected from the Earth's surface
  • Most thermal energy is absorbed and re-emitted back from the Earth’s surface
• The energy passes through the atmosphere where some thermal energy passes straight through and is emitted into space

  • But some thermal energy is absorbed by greenhouse gases, such as carbon dioxide and methane, and is re-emitted in all directions
• Greenhouse effect - reduces the thermal energy lost into space and traps it within the Earth’s atmosphere, keeping the Earth warm
• As the concentration of greenhouse gases in the atmosphere increases due to human activity, more thermal energy is trapped within the Earth's atmosphere causing the Earth’s average temperature to rise (global warming)

  • This process is called the enhanced greenhouse effect
• Diagram showing how the greenhouse effect occurs

  A) sun's

  B) rays

  C) atmosphere

  D) energy

  E) absorbed

  F) earth's

  G) surface

  H) re-emitted

  I) longer

  J) infrared

  K) thermal

  L) atmosphere

  M) thermal energy

  N) carbon

  O) dioxide

  P) greenhouse

  Q) gas

  R) tre-emitted

  S) directions

  T) trapped

  U) hotter

  V) emitted

  W) thermal

  X) atmosphere

  Y) space

  
• Consequences of global warming

  • Climate change due to the increase in Earth’s temperature
  • Water levels will rise as glaciers melt because of high temperatures, causing flooding in low-lying countries
  • Extinction of species due to the destruction of natural habitats
  • Migration of species as they will move to areas that are more habitable (no droughts)
  • Spread of diseases caused by warmer climate
  • Loss of habitat due to climate change (animals that live on glaciers or in low-lying countries)
• Two of the main environmental issues are climate change and acid rain

  • There are strategies that can be used to reduce the impact of these issues
• The production of greenhouse gases, specifically carbon dioxide and methane, needs to be reduced drastically to reduce climate change
• Some measures that can be taken to reduce carbon emissions include (1):

  • Being more ‘responsible consumers’ of energy by:
  • Using hydrogen and renewable energy supplies such as solar or wind energy instead of burning fossil fuels
  • Using more fuel-efficient vehicles, e.g. electric and hybrid cars
  • Reducing the number of vehicles on the road, e.g. using public transport, car-sharing
  • Recycling or reusing products made from crude oil and its derivatives
  • Reducing household energy consumption, e.g. turning lights out, using more efficient appliances
• Some measures that can be taken to reduce carbon emissions include (2):

  • Reducing deforestation and / or re-forestation
  • Planting more trees, can help reduce the amount of atmospheric carbon dioxide through photosynthesis
• Reducing methane emissions

  • Reduce the amount of livestock farming
  • Methane is produced during digestion in animals
• Strategies to reduce acid rain

  • Acid rain is caused by oxides of nitrogen and sulfur dioxide
  • The effects of acid rain can be reduced by decreasing the amount of oxides of nitrogen and sulfur dioxide that are produced
  • Catalytic converters in vehicles can be used to remove oxides of nitrogen
• Reducing sulfur dioxide emissions

  • Using fuels which contain low levels of sulfur
  • Flue gas desulfurisation
  • This is the main way to reduce sulfur dioxide emissions
  • Waste gases from coal fired power stations are passed into a scrubbing chamber
  • They are sprayed with a wet slurry of calcium oxide and calcium carbonate
  • The calcium compounds react with sulfur dioxide to produce calcium sulfate
• • Sulfur dioxide scrubber
  • The scrubber sprays a lime slurry over the waste gases to remove 90 - 95% of the sulfur dioxide

  A) calcium oxide

  B) calcium carbonate

  C) slurry

  D) clean

  E) 90-95

  F) sulfur dioxide

  G) chimney

  H) calcium sulfate

  I) waste

  J) power

  
• There are many other ways that carbon dioxide, methane, oxides of nitrogen and sulfur dioxide can be reduced, e.g. by reducing energy usage to reduce CO2 emissions but it is only the examples stated above that you need to know
• These compounds (NO and NO2) are formed when nitrogen and oxygen react in the high pressure and temperature conditions of internal combustion engines and blast furnaces

  • Exhaust gases also contain unburned hydrocarbons and carbon monoxide
• Cars are fitted with catalytic converters which form a part of their exhaust systems

  • Their function is to render these exhaust gases harmless
• Catalytic converters

  • They contain a series of transition metal catalysts including platinum and rhodium
  • The metal catalysts are in a honeycomb within the converter to increase the surface area available for reaction
• A series of redox reactions occurs in the catalytic converter which neutralises the pollutant gases

  • Carbon monoxide is oxidised to carbon dioxide: 2CO + O2 → 2CO2
  • Oxides of nitrogen are reduced to N2 gas:
  • 2NO → N2 + O2
  • 2NO2 → N2 + 2O2
• A single reaction can summarise the reaction of nitrogen monoxide and carbon monoxide within a catalytic convertor:

  • 2NO + 2CO → N2 + 2CO2
• Catalytic converters are designed to reduce the polluting gases produced in car exhausts

  A) CO2

  B) N2

  C) O2

  D) honeycomb

  E) CO

  F) NO

  G) O2

  
• Unburned hydrocarbons can also be oxidised to carbon dioxide and water:

  • C8H18 + 12½O2 → 8CO2 + 9H2O