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  2. AIR POLLUTION • What are the major air pollutants in the world ? • Where are they come from ? • What and how are the influences to the environment associated with the pollutants ? • How to determine the pollutants are harmful ? • How to reduce the air pollution problem ?

  3. Major air pollutants in the world • Carbon monoxide ( CO ) • Sulphur dioxide ( SO2 ) • Nitrogen oxides ( NO ; NO2 ) • Hydrocarbons • Particulates • Ozone ( O3 ) • Chlorofluorocarbons ( CFCs )

  4. Sources of the pollutants ( I ) • CO – incomplete combustion of carbon-containing fuels. ( e.g. petrol , coal and wood ) • SO2 – burning fossil fuels. ( e.g. fuel oil and coal ) • NO, NO2 – petrol- or diesel-burning engines and coal/oil furnaces.

  5. Sources of the pollutants ( II ) • Hydrocarbons – evaporation of petrol , diesel and solvents when expose to air ; car exhaust ( unburnt hydrocarbons ) • O3 – reaction of oxygen gas with free atoms of oxygen. • Particulates – refuse incineration, factories, diesel vehicles, construction sites, and coal/charcoal burners.

  6. Effects of polluted air on the environment ( I ) Carbon monoxide : This is a poisonous gas. It combines with haemoglobin in red blood cell to form a stable complex, carboxyhaemoglobin. The haemoglobin is thus not available for carrying oxygen to the various parts of the body. Hence, CO can cause death even in relatively low concentration. ☆ CO + haemoglobin ―> carboxyhaemoglobin

  7. Effects of polluted air on the environment ( II ) Sulphur dioxide : It can cause damage to respiratory systems and increase in asthma attacks. Besides, SO2 in air will cause acid rain also. Particulates : It can impair lung function by constricting respiratory passage and damaging lung tissue, and cause respiratory illness. Besides, certain particles are suspected to cause cancer.

  8. Effects of polluted air on the environment ( III ) Nitrogen oxides : The oxides in air will also cause acid rain. Moreover, NO2 gives rise to photochemical smog. Besides, it is a poisonous gas that can damage lung tissue and blood vessels when present in high concentration.

  9. Effects of polluted air on the environment ( IV ) Ozone : It irritates the eyes, aggravates asthma and damage plants. Hydrocarbons : It can cause photochemical smog. Certain hydrocarbons ( e.g. benzene ) are known carcinogens.

  10. Effects of polluted air on the environment ( V ) Conclusion : • High levels of pollutants can cause a variety of symptoms including headaches, irritation of eyes, nose, and throat, nausea and general ill feeling, or even respiratory diseases. • Since plants are generally more sensitive to the pollutants, some species of plants such as lichens will not grow in cities due to the high level of air pollutants.

  11. Effects of polluted air on the environment ( acid rain I ) FORMATION OF ACID RAIN : • Unpolluted rainwater is slightly acidic and has a pH of 5.6 . • Acid rain is caused by : In atmosphere : 1.1. 2SO2 + O2―> 2SO3 1.2. SO3 + H2O ―> H2SO4 2. SO2 + H2O ―> H2SO3 3.1. 2NO + O2―> 2NO2 3.2. 4NO2 + 2H2O +O2―> 4HNO3

  12. Effects of polluted air on the environment ( acid rain II ) EFFECT OF ACID RAIN : • Calcium metabolism in fresh water will lead to poor health and stunted growth. Hence, diversity and population of some fresh water species will be reduced. • Since absorption of cations by plants will be affected, the death of plants results. • Acid rain corrodes metals and accelerates the deterioration of building, rock and statue.

  13. Effects of polluted air on the environment ( photochemical smog I) • Photochemical smog is a mixture of pollution which includes particulates, nitrogen oxides, aldehydes,ozone, peroxyacetyl nitrate(PAN), unreacted hydrocarbons, etc. • It is formed by the combination of sunlight, the catalysis by particulates and the abundant pollutants present in cities. • It is a brown haze and painful eyes.

  14. Effects of polluted air on the environment ( photochemical smog II) Formation of photochemical smog : • NO2 + UV light ―> NO + O • O + O2―> O3 • O + hydrocarbons ―> aldehydes • O3 + hydrocarbons ―> aldehydes • Hydrocarbons + O2 + NO2―> lachrymatory substances ( e.g. PAN molecule )

  15. Effects of polluted air on the environment ( photochemical smog III) Effect of photochemical smog : • It causes headaches, eye, nose and throat irritation, impaired lung function, coughing and wheezing. • It causes rubbers and fabrics to deteriorate. • It damages plants, leading to the loss of crops.

  16. Sources of ozone • It is formed by the reactions between nitrogen oxides and hydrocarbons in sunlight,and from air by electric sparks which occur in car engines or electrical appliances,or during lightning. • O2 + UV→O + O • O + O2 →O3

  17. Properties of ozone • It is pale blue gas with a pungent odour.It is harmless in small concentration.If the concentration rises above 100ppm ,it will cause respiratory problems and headaches. • It is reactive when remaining in the atmosphere for a long time.

  18. Desirability of ozone layer in the stratosphere • The ozone layer in the stratosphere filters out 99% of dangerous ultra-violet radiation from the sun.A thinning of the ozone layer may lead to an increase in the incidence of the skin cancer and eye cataract,and a decrease in yield of crops.

  19. Chlorofluorocarbons(CFCs) and its uses • CFCs are a family of compounds containing chlorine,fluorine and carbon. • CFCs have a wide range of uses: • As aerosol propellants • As solvents in cleaning electronic compounds and metals • As refrigerants • As blowing agents in foam plastic manufacturing

  20. Accumulation of chlorofluorocarbons in the stratosphere • CFCs are widely used for many years,so they are easily escape into the atmosphere during use. • They are so unreactive that they break down very slowly in the atmosphere.For example,CCl3F has a lifetime of 75 years. • They are relatively insoluble in water and so not removed either rainfall or by dissolution in the ocean.

  21. How CFCs lead to the depletion of ozone layer I • Ozone in the stratosphere undergoes photodissociation by absorbing ultra-violet radiation: O3+UV→O2+O • The free O atom further reacts with another molecule of ozone: O+O3→O2+O2

  22. How CFCs lead to the depletion of ozone layer II • This has the effect of reducing the concentration of ozone in the stratosphere .However,ozone is being made at the time. • The rate of making and destroying ozone is equivalent.Thus,a constant concentration of ozone is maintained.

  23. How CFCs lead to the depletion of ozone layer III • CCl3F+UV →CCl2F*+Cl* • The Cl* that is given a free radicals are very effective in destroying ozone. • Cl*+O3 →ClO*+O2 • ClO*+O →Cl*+O2 • This has the effect of disturbing the production and destruction of ozone. • The most worrying is the fact that Cl*is regenerated in the above process.

  24. Control of the ozone depletion problem • The first international effort to protect the ozone layer came in January 1987 when 24 countries signed the Montreal Protocol on Substances That Deplete the Ozone Layer which called for a cut back of the CFC production in stages. • The protocol was amended in 1990 when 93 countries pledged to stop all production of CFCs and other ozone depleting substances by 2000.

  25. What Hong Kong should do to reduce air pollution • Reducing pollution from car exhausts • Controls on excessive smoke emissions from motor cars • Using unleaded petrol or petrol with low lead content • Installation of catalytic converters • Reducing pollution from electric power stations, factories and incinerators • using fuels of low sulphur content • Reduction of emissions from chimney stacks • Control of dark smoke emission • Town planning

  26. Possible alternatives for chlorofluorocarbons I • Hydrochlorofluorocarbons(HCFCs) such as CF3CHCl2 • They break down more quickly in the atmosphere. • Hydrofluorocarbons(HCFs) such as CF3CH2F • They have no chlorine and thus are “ozone safe”.However,they are toxic.

  27. Possible alternatives for chlorofluorocarbons II • Hydrocarbons such as butane and propane • They are cheap,contain no chlorine and “ozone safe”.However,they are flammable and poisonous. • Water and steam • They are effective for some cleaning applications and thus can replace some CFCs as solvents in cleaning.

  28. Bye Bye!!!