1. Chapter 13 Air & Atmosphere

3. What does air consist of? Air is a mixture of several gases. As air is a mixture, its composition varies from time to time and from place to place . Gas Composition by volume Nitrogen 79% Oxygen 20% Noble gases (mainly argon) & carbon dioxide 1%

4. 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 .

6. Air Pollution 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 . Click on the video on Air Pollution.

8. Pollutants Major Sources Harmful Effects (b) Oxides of nitrogen (eg. nitrogen monoxide, NO & nitrogen dioxide, NO 2 . 1) Reactions that occur in car engines ( internal combustion engines) 2) From lightning Nitrogen reacts with oxygen in the air to form nitrogen monoxide. N 2 (g) + O 2 (g)  2NO (g) Nitrogen monoxide reacts with oxygen to form nitrogen dioxide (NO 2 ). 2NO (g) + O 2 (g)  2NO 2 (g) 1) Eye irritation 2) Breathing difficulties 3) Lung inflammation (bronchitis) 4) Acid rain

10. Other air pollutants include - unburnt hydrocarbons - methane - ozone Other Pollutants Unburnt hydrocarbons 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 .

13. Click on the animation on Acid Rain

20. 2 ways of minimising the effects of sulfur dioxide pollution: Flue Gas Desulfurisation 1. Remove sulfur from fossil fuels before burning. However, this method is too expensive and difficult. 2. Remove sulfur dioxide from the waste gases (flue gases) from burning. - Process known as desulfurisation

21. What Happens in Desulfurisation? Sulfur dioxide reacts with an aqueous suspension of calcium carbonate to form solid calcium sulfite . CaCO 3 (s) + SO 2 (g)  CaSO 3 (s) + CO 2 (g) The calcium sulfite is further oxidised to calcium sulfate by atmospheric oxygen. CaSO 3 (s) + O 2 (g)  2CaSO 4 (s)

22. Control of Air Pollution in Singapore • Prohibition of the use of open fires for the disposal of domestic and industrial wastes • Introduction of unleaded petrol and phasing out of leaded petrol • Reduction of the permissible level of sulfur in diesel • Fitting of all petrol-driven vehicles with catalytic converters

24. Is our ozone layer being depleted?

25. What is ozone? Ozone is a bluish, very reactive gas, whose molecule is made by three oxygen atoms . At low altitudes, it can cause breathing difficulties and photochemical smog. However, in the stratosphere, the ozone layer shields us from ultraviolet radiation from the sun. Note: UV radiation can cause skin cancer, genetic mutations and cataracts. Click on the video on Ozone.

26. What is causing the depletion of ozone in the stratosphere? Chlorofluorocarbons (CFCs) . - compounds containing the elements carbon, fluorine and chlorine. - widely used as propellants for aerosols and as coolants in refrigerators and air conditioners .

28. The Carbon Cycle Click on the video on Carbon cycle The mechanism that maintains the level of carbon dioxide in the atmosphere is called the carbon cycle .

31. What are the other types of greenhouse gases? Methane (CH 4 ) and nitrous oxide (N 2 O)

32. The Greenhouse Effect The natural greenhouse effect is crucial for maintaining the proper temperature needed to sustain life on Earth. Without these greenhouse gases, Earth’s surface temperature would be –40 °C and it would be permanently covered with ice.

33. Global Warming Greenhouse gases, such as carbon dioxide, are building up rapidly in the atmosphere. Why? Human activities like the burning of fossil fuels and large scale cutting down of forests

35. Consequences of Global Warming • a decrease in crop yields world-wide because the areas that are currently covered by vegetation may become deserts, • the melting of large quantities of ice in the North Pole and South Pole. This will cause the levels of oceans to rise and flood low-lying countries such as the Netherlands. • the rapid evaporation of water from the Earth’s surface. When this happens, carbon dioxide dissolved in the oceans will be driven out into the atmosphere. This adds further to the greenhouse effect. Click on the video on global warming.