Atmospheric Pollutants

• Major Sources of Atmospheric Pollutants:

  • The combustion of fossil fuels is the major source of atmospheric pollution
  • Fossil fuels include: coal, oil, natural gas, oil shales and tar sands
  • Non-renewable fossil fuels are obtained from crude oil by fractional distillation
  • Petrol is used as a fuel in cars, kerosene is used to fuel aircraft and diesel oil is used as a fuel in some cars, trucks and heavy vehicles such as tanks and trains
  • Coal is used in power stations and also steel production
  • Natural gas consists mainly of methane, CH4
• Major Sources of Atmospheric Pollutants:

  • There are finite amounts of fossil fuels and they all contribute to pollution and global warming
  • All these fuels contain carbon, hydrogen and small quantities of sulfur
• Combustion Products:

  • The burning of fossil fuels releases the gases carbon dioxide, carbon monoxide, oxides of nitrogen and oxides of sulfur
  • In addition incomplete combustion of the fuels gives rise to unburned hydrocarbons and carbon particulates
• Complete versus Incomplete Combustion:

  • A fuel is a substance which releases energy in an exothermic reaction
  • When the fuel is a hydrocarbon then water and carbon dioxide are the products formed
  • Hydrocarbon compounds undergo complete and incomplete combustion
  • Complete combustion occurs when there is excess oxygen
  • For example, the combustion equation for propane is:

  C3H8 + 5O2 → 3CO2 + 4H2O
• Incomplete Combustion:

  • Incomplete combustion occurs when there is insufficient oxygen to burn
  • It occurs in some appliances such as boilers and stoves as well as in internal combustion engines
  • The products of these reactions are unburnt fuel (soot), carbon monoxide and water
  • Methane for example undergoes incomplete combustion in an oxygen-poor environment:

  2CH4 + 3O2→ 2CO + 4H2O

  CH4 + O2→ C + 2H2O
• The Problems Caused by Pollutants:

  Carbon Monoxide & Soot

  • Carbon monoxide is an extremely poisonous gas as it combines with haemoglobin in blood and prevents it from carrying oxygen
  • It is particularly malevolent as it is colourless and odourless, making it difficult to detect
  • A lack of oxygen supply to the brain can lead to fainting, coma or in worst case scenarios, even death
• The Problems Caused by Pollutants:

  Carbon Monoxide & Soot

  • The carbon particles released from incomplete combustion clump together to form soot which gradually falls back to the ground
  • Soot causes respiratory problems and covers buildings and statues, making them look unclean and accelerating corrosion
• Statues and monuments in very polluted areas become blackened over time from soot:

  
• Sulfur Dioxide:

  • Sulfur dioxide is a colourless, pungent smelling gas that is a major air pollutant responsible for acid rain
  • The sulfur dioxide released mixes with clouds and readily dissolves in rainwater
  • SO2 is a non-metal oxide so it forms an acidic solution in water, hence forming acid rain
  • Acid rain causes corrosion to metal structures, buildings and statues made of carbonate rocks
  • It causes damage to aquatic organisms, pollutes crops and water supplies, and irritates lungs, throats and eyes
• Oxides of sulfur and nitrogen contribute to the formation of acid rain:

  
• Oxides of Nitrogen:

  • Oxides of nitrogen come largely from vehicle exhausts and also contribute to acid rain
  • Aside from acid rain, oxides of nitrogen produce photochemical smog and breathing difficulties, in particular for people suffering from asthma