Air Pollutants

• Air pollutants


  • air pollutants are substances which harm living things and affect the environment
  • also known as atmospheric pollutants
• Air pollutants - Carbon monoxide(CO)

  • Carbon monoxide comes from incomplete combustion of carbon-containing fuels
  • combines with haemoglobin in red blood cells and reduces ability to transport oxygen, thus causing death
• Air pollutants - Sulfur Dioxide(SO2)


  • Sulfur dioxide comes from combustion of sulfur-containing fossil fuels or volcanic eruptions
  • causes irritation of lungs and eyes and breathing difficulties
  • react with oxygen to form acid rain. Acid rain kills plants and aquatic life and corrodes marble and metal structures
• Air Pollutants - Oxides of Nitrogen (NO, NO2)


  • Oxides of nitrogen come from combustion of vehicles and lightning (high temperature)
  • causes irritation of lungs and eyes and breathing difficulties
  • react with oxygen to form acid rain. Acid rain kills plants and aquatic life and corrodes marble and metal structures
• Air Pollutants - Methane (CH4)


  • methane comes from decompositon of dead organic matter and waste gases released due to digestion in cattle
  • it is a greenhouse gas that contributes to global warming
• Air Pollutants - Unburnt Hydrocarbons (CxHy)


  • Unburnt hydrocarbons come from combustion in engines of vehicles and chemical plants
  • causes irritation of lungs and eyes and breathing difficulties
  • react with oxides of nitrogen in the presence of sunlight to form photochemical smog which pollutes the air. Photochemical smog appears as a brown haze
• Air Pollutants - Ozone (O3)


  • Ozone comes from reaction between oxides of nitrogen and unburnt hydrocarbons in the presence of sunlight or lightning (high temperature)
  • causes irritation of lungs and eyes and breathing difficulties
  • causes headache and chest pain
  • slows down photosynthesis, thus affecting crops
• Acid Rain (memories formulas)


  • rainwater containing high levels of sulfuric acid and nitric acid
  • Sulfuric acid and nitrogen dioxide are acidic oxides and react with oxygen and water to form sulfuric acid and nitric acid respectively
  • causes corrosion of metal bridges and structures
  • causes corrosion of buildings or monuments made up of calcium carbonate
  • acidification of lakes and rivers, which harms aquatic life
  • leaches nutrients from the soil, which affects the growth of plants

  
• Reducing Air Pollution


  Ways to reduce air pollution include :

  1. using a catalytic converter to remove certain air pollutants from exhaust gases
  2. carrying out flue gas desulfurisation to remove sulfur dioxide
  3. using low sulfur fuels to reduce the emission of sulfur dioxide from vehicle engines
• Catalytic Converters

  • fitting catalytic converters to exhaust pipes can help to reduce the amount of air pollutants such as carbon monoxide, oxides of nitrogen and unburnt hydrocarbons
  • catalysts used in catalytic converters are transition metals like platinum and rhodium
• Catalytic Converter Redox Reactions


  • In the catalytic converter, redox reaction convert harmful exhaust gases into harmless gases

  1. Nitrogen monoxide reacts with carbon monoxide to form nitrogen and carbon dioxide 2NO(g) + 2CO(g) -> 2CO2(g) +N2(g)
  2. Carbon monoxide is oxidised to form carbon dioxide 2CO(g) + O2(g) -> 2CO2(g)
  3. Oxides of nitrogen are reduced to nitrogen 2NO(g) + 2CO(g) -> N2(g) + 2CO2(g)
  4. Unburnt hydrocarbons such as octane are oxidised to carbon dioxide and water vapour 2C8H18(g) + 25O(g) -> 16CO2(g) + 18H2O(g)
• Flue Gas Desulfurisation


  • the exhaust or waste gases produced by power plants that burn sulfur-containing fossil fuels are known as flue gas
  • Flue gas desulfurisation is the process of removing sulfur dioxide from the waste gases formed when fossil fuels undergo combustion, reducing the amount of sulfur dioxide that is released into the atmosphere

  
• • Flue Gas Desulfurisation Reactions

  • flue gas sulfur dioxide is reacted with the calcium carbonate to form calcium sulfite and carbon dioxide CaCO3(s) + SO2(g) -> CaSO3(s) + CO2(g)
  • The calcium sulfite formed is further oxidised by oxygen in the atmosphere to calcium sulfate 2CaSO3(s) + O2(g) -> 2CaSO4(s)
  • Calcium oxide, which is a base, can also be used to react with the acidic sulfur dioxide CaO(s) + SO2(g) -> CaSO3(s)