20. Air

Composition
  • Nitrogen: 78%
  • Oxygen: 21%
  • Noble gases: 1%
  • Carbon dioxide: 0.03%
  • Water vapour: Variable

Carbon Monoxide
  • Source: Incomplete combustion of carbon-containing fuels.
  • Effect: A poisonous and odourless gas binds irreversibly with haemoglobin in blood, reducing ability of the blood to carry oxygen, thus causing death.

Methane
  • Source: Bacterial decay of vegetable matter.
  • Effect: A greenhouse gas which causes global warming.

Oxides of Nitrogen
  • Source: During lightning activity & Reaction between oxygen & nitrogen in internal combustion engines at high temperatures.
  • Effect: Nitrogen oxides reacts with oxygen and water vapor to form nitric acid which dissolves in water to form acid rain which causes corrosion of limestone buildings and metal structure.

Sulfur Dioxide
  • Source: During volcanic eruptions & Combustion of fossil fuels containing sulfur as an impurity
  • Effect: Sulfur dioxide reacts with oxygen and water vapor to form sulfuric acid which dissolves in water to form acid rain which causes corrosion of limestone buildings and metal structure.

Ozone
  • Source: Action of UV light on oxides of nitrogen, carbon monoxide and unburnt hydrocarbons.
  • Effect: Forms photochemical smog which causes breathing difficulties, especially for asthma sufferers.

Unburnt Hydrocarbons
  • Source: Due to incomplete combustion of fuel from internal combustion engines of vehicles.
  • Effect: Reacts with nitrogen oxides and carbon monoxide in the presence of UV light to produce ozone

Measures
  • To remove carbon monoxide, unburnt hydrocarbons and oxides of nitrogen: Install catalytic converters in cars
  • To remove sulfur dioxide: Flue gas desulfurisation
  • To reduce effect of acid rain: Burn fuels which contain little or no sulfur. OR Use of catalytic converter in cars and removal of acidic gases in power stations.

Ozone Layer
  • The ozone layer forms a thin shield in the upper atmosphere, protecting life on Earth from the sun's ultraviolet (UV) rays.
  • Chlorofluorocarbons (CFCs) release chlorine atoms in the presence of sunlight, reacting with the ozone molecules, depleting the ozone layer.
  • Excess UV rays reach the earth’s atmosphere, causing increased skin cancer & eye cataracts.

Carbon Cycle
  • Carbon dioxide is released into the atmosphere by combustion, decay and respiration.
  • Carbon dioxide is removed from the atmosphere by plants during photosynthesis. The percentages of carbon dioxide and oxygen is kept constant.

Ozone Layer
  • Carbon dioxide and methane are the main greenhouse gases that cause global warming.
  • Consequences of global warming:
  1. Ice caps melt
  2. Sea level rises, causing floods to low-lying lands.
  3. Big changes in global climate, equatorial countries will experience more rain but others might experience drought.
  4. Disruption to food production