Air

• The present composition of gases in the atmosphere has not changed much in 200 million years

  • About four-fifths of the air is nitrogen and one-fifth is oxygen
  • The remaining gases include carbon dioxide, water vapour and trace quantities of the noble gases
• Pie chart of the current atmosphere

  A) argon

  B) noble gases

  C) 0.9%

  D) carbon dioxide

  E) 0.04%

  F) Oxygen

  G) 21%

  H) Nitrogen

  I) 78%

  
• In addition to the gases present naturally in our atmosphere, other gases are present due to human activities and are classed as air pollutants
• Carbon dioxide sources:

  • Complete combustion of carbon-containing fuels such as fossil fuels
  • For example, the complete combustion of methane:
  • CH4 + 2O2 → CO2 + 2H2O
• Adverse effects of carbon dioxide:

  • Increases global warming, which leads to climate change
• Carbon Monoxide Sources:

  • Incomplete combustion of carbon-containing fuels such as fossil fuels
  • For example, the incomplete combustion of gasoline / octane
  • C8H18 + 9O2 → 5CO + 2CO2 + 9H2O
• Adverse effects of carbon monoxide:

  • Toxic / poisonous
  • It combines with haemoglobin in the blood and prevents it from carrying oxygen
• Particulates Sources:

  • Incomplete combustion of carbon-containing fuels such as fossil fuels can also produce particulates of carbon (soot)
  • For example, the incomplete combustion of methane can produce CO and C:
  • 2CH4 + 3O2→ 2CO + 4H2O
  • CH4 + O2→ C + 2H2O
• Adverse effects of particulates:

  • Respiratory problems
  • Cancer
• Methane Sources:

  • Waste gases from digestive processes of animals
  • Decomposition of vegetation
  • Bacterial action in swamps, rice paddy fields and landfill sites
• Adverse effects of methane:

  • Increases global warming, which leads to climate change
• Oxides of Nitrogen Sources:

  • Reaction of nitrogen with oxygen in the presence of high temperatures, e.g. in car engines, high-temperature furnaces and when lightning occurs
  • It is also a product of bacterial action in the soil
• Adverse effects of oxides of nitrogens:

  • Produces photochemical smog
  • Dissolves in rain to form acid rain which causes corrosion to metal structures, buildings and statues made of carbonate rocks, damage to aquatic organisms
  • Pollutes crops and water supplies
  • Irritates lungs, throats and eyes and causes respiratory problems
• Sulfur dioxide sources:

  • Combustion of fossil fuels containing sulfur compounds
  • S + O2 → SO2
  • Power stations are a major source of sulfur dioxide
• Adverse effects of sulfur dioxide:

  • Dissolves in rain to form acid rain with similar effects as the acid rain caused by oxides of nitrogen