1. What does air consist of?
Air is a mixture of several gases.
Gas
Composition by volume
Nitrogen
78 – 79%
Oxygen
20%
Carbon dioxide
0.03%
Water vapour
0 – 5%
Noble gases
< 1%
As air is a mixture, its composition varies from time to time and from place to place.
Copyright © Marshall Cavendish International (Singapore) Pte. Ltd.

2. Separation of Air into its Components
Air is first cooled and compressed into liquid.
Liquid air is then separated into its constituents (or fractions) by fractional distillation.
Copyright © Marshall Cavendish International (Singapore) Pte. Ltd.

3. Air Pollution Much of the air we breathe in is not clean.
Air pollution is the condition in which air contains a high concentration of certain chemicals that may harm living things or damage non-living things.
Air pollution is caused by solid particles and poisonous gases in the air.
These air pollutants include carbon monoxide, oxides of nitrogen and sulphur dioxide.
Copyright © Marshall Cavendish International (Singapore) Pte. Ltd.

4. Carbon Monoxide Carbon monoxide (CO) is a poisonous gas.
It is colourless and odourless.
It is produced by the incomplete combustion of carbon-containing fuels.
Much of the carbon monoxide in the air comes from the incomplete combustion of petrol in car engines.
Copyright © Marshall Cavendish International (Singapore) Pte. Ltd.

5. Oxides of nitrogen
Oxides of nitrogen include nitrogen monoxide (NO) and nitrogen dioxide (NO2).
Oxides of nitrogen are produced in 2 ways:
1st way: in car engines or factories
2nd way: during thunderstorms
Copyright © Marshall Cavendish International (Singapore) Pte. Ltd.

6. 1st way:
In a car engine or chemical factory, where the temperature is very high, nitrogen combines with oxygen in the air to form nitrogen monoxide (NO).
N2(g) + O2(g)  2NO(g)
Nitrogen monoxide, a colourless gas, reacts with oxygen to form a brown gas, nitrogen dioxide.
2NO(g) + O2(g)  2NO2(g)
Copyright © Marshall Cavendish International (Singapore) Pte. Ltd.

7. 2nd way: the heat energy released by lightning
During thunderstorms,
the heat energy released by lightning
causes nitrogen and oxygen in the air to react
to form oxides such as nitrogen monoxide and nitrogen dioxide.
Copyright © Marshall Cavendish International (Singapore) Pte. Ltd.

8. Sulphur dioxide
The major source of sulphur dioxide (SO2) is the combustion of fossil fuels such as coal and crude oil (petroleum).
Fossil fuels contain sulphur.
When they are burnt, sulphur is converted to sulphur dioxide.
S(s) + O2(g)  SO2(g)
Sulphur dioxide is also produced during volcanic eruptions.
Copyright © Marshall Cavendish International (Singapore) Pte. Ltd.

9. Other Pollutants
Other air pollutants include unburnt hydrocarbons, methane, lead and ozone.
Unburnt hydrocarbons and lead are released in car exhaust.
Methane is a colourless and odourless gas produced when plant and animal matter decay.
It is also produced from the decay of rubbish in landfills.
Methane is a greenhouse gas.
Copyright © Marshall Cavendish International (Singapore) Pte. Ltd.

10. Effects of Pollution Air pollutant Effects carbon monoxide
CO causes headaches, fatigue, breathing difficulties and even death.
sulphur dioxide
These gases irritate the eyes and cause breathing difficulties by irritating the lungs.
• High levels of SO2 and oxides of nitrogen also lead to inflammation of the lungs (bronchitis).
• SO2 and NO2 form acid rain, which corrodes buildings, harm aquatic life and plants.
oxides of nitrogen
Copyright © Marshall Cavendish International (Singapore) Pte. Ltd.

11. Why is carbon monoxide harmful?
CO reacts with haemoglobin in blood to form carboxyhaemoglobin.
Carboxyhaemoglobin is extremely stable.
As a result, haemoglobin cannot transport oxygen to the rest of the body.
Copyright © Marshall Cavendish International (Singapore) Pte. Ltd.