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10.5 Acid rain  the invisible threat

Discover the pH value of rainwater and why it is acidic. Learn about the causes and effects of acid rain on humans and the environment. Find out how we can control acid rain.

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10.5 Acid rain  the invisible threat

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  1. 10.5Acid rain  the invisible threat

  2. Do you know ? p.29 What is the pH value of rainwater? Why is rainwater acidic?

  3. + Carbon dioxide rainwater rain pH value of rainwater is about 5.6 (with carbonic acid) (acidic gas) weak acid Acid rain: pH value is lower than 5.6

  4. + + oxygen rainwater sulphuric acid sulphur dioxide (strong acid) + rainwater nitric acid nitrogen oxides (strong acid) Cause of acid rain p.29 Air pollutants (acidic gas) (acidic gas) Sulphuric acid and nitric acid make pH value of rainwater lower than 5.6

  5. Vehicles、factories and power stations burn coal and crude oil and so acidic gases are formed.

  6. sulphur dioxide + sulphur oxygen - Coal and crude oil contain sulphur. When power stations and vehicles burn these fuels, sulphur dioxide will be released.

  7. + nitrogen oxygen nitrogen oxides - Under high temperature of burning,nitrogen and oxygen in air will have chemical reaction and nitrogen oxides will be formed.

  8. Parthenon (巴特農神殿) is made of marble (大理石). After 24 centuries, it was only a little corroded. The speed of corrosion increased rapidly in the recent 30 years. Some parts of the building collapsedbecause ofacid rain.

  9. sulphur dioxide + sulphur oxygen + nitrogen oxygen nitrogen oxides Some natural phenomena may also form acidic gases. Volcanic explosion releases sulphur dioxide Lightning forms nitrogen oxides p.29

  10. Do you know ? What are the effects of acid rain on humans andtheenvironment?

  11. Effects of acid rain p.30 Corroding buildings Corroding metals Damaging plants Killing aquatic life

  12. lime water metal dilute hydrochloric acid Corroding buildings - From the results of Experiment Centre 10.9 and 10.10, we know that acids are corrosive to metals and calcium carbonate. => Acid rain corrodesbuildings or statues made ofmetals or marble. - If therain is more acidic, the speed of corrosionwill be higher.

  13. Damaging our forests -Acid rain: =>dissolves some essential nutrients in soil. =>affects absorption of required nutrients of the plants. =>affects healthy growth of plants and kills them.

  14. Do you know ? In the New Territories, some farmers found that leaves of vegetables turn yellow and ‘get burns’ after raining.

  15. Killing aquatic life - Acid rain falls into rivers and lakes and makes the water acidic. - When thepH value of water is below 5, most fishes will die.

  16. - Besides, acid rain: =>dissolves some toxic minerals in soil. => leads the toxic minerals flowing into rivers and lakes. =>kills aquatic life and destroys eggs of fishes.

  17. Effects of acid rain on humans - Acid rain may cause respiratory diseases and skin allergy.

  18. Do you know ? Rainwater with the highest acidity In 1983, pH value of acid rain in Scotland isas low as at 1.87. More acidic thanlemon juice!

  19. Is the acid rain problem serious? p.33 -Acid rain is not new. - Cities and industries develop continuously. It was first observed 100 years ago when factories were concentrated in European cities. =>Damaging effect of acid rain is more obvious. => Concentration of air pollutants increases

  20. - The following map shows ‘Global acid rain pollution’ problem: pH lower than 4.2 pH 4.2 - 4.5 pH4.6 – 5.0 region with mild acid rain

  21. Share your view Is there any acid rain problem in Hong Kong? The following questions may help you to find the answer. >What is the main source of air pollutants in Hong Kong? >What is thesituation of air pollution in China? >Willair pollutants in China affect Hong Kong?

  22. p.33 How can we control acid rain? - To control acid rain, we should take appropriate measures toreduce the formation ofacidic gases. What are the methods to reduce the formation ofacidic gases?

  23. Methods of reducing acidic gas exhaust: 1Save resources and reduce burning of fossil fuels. 2 Use fuel with lower sulphur content.

  24. 3 Use the energy sources without producing acidic gases. e.g. solar power, wind power...

  25. catalytic converter 4 Remove the acidic gases after burning. e.g.catalytic converter in cars 5 Educate the public on effects of acid rain and the methods of reducing acid rain.

  26. - Acid rain problem in Hong Kong is not a local problem, but a regional problem. - The HKSARgovernment and the Guangdong Provincial government join togetherto control acid rain. e.g. Set air pollutant emission reduction targets => Reduce the regional emission of sulphur dioxide by 40% and nitrogen oxides by 20%before 2010.

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