Air Pollution

1. Air Pollution • 1. What is air pollution? • 2. Sources of air pollutants • 3. Air pollutants • 4. Ozone and CFC • 5. Photo chemical smog • 6. Acid rain • 7. Ways to reduce air pollution

2. What is air pollution?? - the presence of undesirable substances in air at a level that is high enough to cause damage to our health or properties

3. Sources of air pollutants human activities • burning of fossil fuel • use of motor vehicles • electric power station • factories • incinerators

4. Burning of fossil fuels causes • air pollutions • incomplete combustion of fuels ----- formation of C (soot , smoke), CO & and unburnt hydrocarbon • burning of sulphur containing fuel ----- giving SO S + O ------> SO • combustion at high tempeature ----- formation of NO & NO from air N+O ------> 2NO 2NO+O -----> NO

5. combustion of leaded petrol ----- forming lead and PbO • burning of coal with some metal compounds ----- giving ash e.g. soot

6. Air pollutants • 1.Carbon monoxide • 2.Nitrogen oxide • 3.sulphur dioxide • 4.lead compounds • 5.unburned hydrocarbons • 6.particulates

7. 1.carbon monoxide • Nature and Sources of the Pollutant:--Carbon monoxide is a colorless, odorless, poisonous gas • formed when carbon in fuels is not burned completely. • e.g.C8H18 + 9O2 3CO2 + 3CO +2C +9H2O

8. Health and Environmental Effects: --Carbon monoxide enters the bloodstream and reduces oxygen delivery to the body's organs and tissues. -Low conc. : causes dizziness,headache, -High conc. :cause unconsciousness and even death

9. 2.nitrogen oxides • Nature and Sources of the Pollutant: -Combustion of fuels in high temperature N2 +O2 NO2 --Car exhaust,factories,power stations

10. Health and Environmental Effects: • Irritate and attack respiratory tracts and the lungs • Form acid rain

11. 3.sulphur dioxide • Nature and Sources of the Pollutant: Burning of fuel which contain sulphur (impurities) -From factories,power station and incineration.

12. Health and Environmental effects: • Harmful respiratory system • Cause cancer and heart problems • Irritate the eyes • Causes acid rain

13. 4.lead cpds. • Nature and Sources of the Pollutant: -Combustion of fuel of cars. -lead are added to increase the burning efficiency

14. Health and Environmental Effects: • Lung diseases • Affects cell and body processes e.g.CNS,heart attract and hypertension • Lack of concentration and memory

15. 5.unburned hydrocarbons • Nature and Sources of the Pollutant:-evaporation of petrol -exhaust of incompletely burnt of fuel(factories ,power plants)

16. Health and Environmental Effects: • Causing cancer • Formation of photochemical smog

17. 6.carbon particulates • Nature and Sources of the Pollutant:-incomplete combustion of fuel -car exhaust and power plants

18. Health and Environmental Effects: • Suspended particulates cause lung cancer and diseases such as tuberculosis

19. Ozone and CFC • Formation of ozone • 1.  Reaction between NO2 and hydrocarbon • 2.  From air by electrical sparks( in car engine) & in electric machine(photo copier) • 3.  From atmospheric O2 by absorption of UV radiation • O2  O + O • O + O2  O3 • O3  O2 + O (dissociation of O3)

20.  it is very important as the screening effect of ozone prevents the harmful UV rays from reaching the earth crust. • * 1 & 2 are formed in lower atm., but 3 is in upper atm.

21. Properties of ozone • 1.pale blue gas • 2.pungent smell • 3.harmless at low concentration • 4.causes breathing problems & headache (if conc. >100 ppm) • Why do we need ozone? • It can filter out 99% if the dangerous UV radiation from the sun. Thus, stop skin cancer, eye contract and crop-yield reduction

22. Properties of CFC • 1.chemically unreactive • 2.low flammability • 3.highly volatile • 4.low toxicity • Uses of CFC • 1.Aerosol propellants eg trichlorofluromethan(CCl3F), dichlorodifluromethane(CCl2F2) • Since CFC is very volatile, it can produce high pressure to propel out eg insecticide

23. 2.Solvents in cleaning agents for electronic component eg tricholorotrifluro ethane ( CCl2F-CClF2 ) • CFC can dissolve grease & be removed by evaporation • 3.Refrigerants eg Freon( CCl2F2) • It is highly volatile that it absorbs heat of vaporization during evaporation => cooling of surrounding

24. 4.Blowing agents in foam plastic manufacturing eg CCl3F • CFC is incorporated into monomers. It is then vaporized by the heat evolved during polymerization. Tiny bubbles in plastic formed. • Why does CFC accumulate in stratosphere? • Since CFC is easily transported, Cl radicals are formed, CFC is insoluble in water,CFC accumulates.

25. How CFC affect ozone concentration. • During last 30 years, there is a drastic change in ozone concentration in stratosphere above Antarctica & Arctic region. • Ozone is related to the release of CFCs to the atm. • CCl3F + UV rays CCl2F* + Cl * • CCl2F2 + UV rays  CClF2* + Cl* • Cl* + O3  ClO* +O2 • ClO* + O3  Cl* + 2O2

26. Controlling the ozone depletion problem • 1.restricting the import • 2.installing recovery unit and recycling units • 3.using substitutes for CFCs • a.HCFCs – lower % mass of Cl • -break down more quickly in atm • -if overuse  still form Cl* • b.HFC – no Cl atom  ozone safe • -it is toxic

27. c.hydrocarbon (propane & butane) • -no Cl  ozone safe • -cheap & readily available • -flmmable and poisonous  can’t be widely used • d.water & steam • - effective in some cleaning application ( vaporizing grease at high temperature)

28. Photochemical Smog • a mixture of pollutants including particulates, NO2, peroxyacetyl nitrate( PAN), ozone, aldehydes, unreacted hydrocarbons ,etc. • Detecting photochemical smog • Brownish haze & painful eyes ---- brown colour is due to NO2 ---- haze is due to particulates & droplets ---- pain felt is due to NO2 , ozone & PAN

29. Factors leading to the formation of photochemical smog • reactants : unburnt hydrocarbons & NO2 • initiating condition : UV rays • catalyst : particulates & other atmospheric pollutants • climatic factor : absence of strong winds will slow down the disappearance of smog • topographical factor : tall buildings will reduce the air flow in a crowded city

30. Formation of photochemical smog • Homolysis of NO2 : • NO2 ------> NO + ‧O • O atoms react with other components & pollutants of air: O + O2 ------> O3 • O + hydrocarbons ------> aldehydes • O3 + hydrocarbons ------> aldehydes • Hydrocarbons + O2 + NO2 ------> • lachrymatory substances ( including PAN )

31. Effect on human health • causes irritation in mucous membranes ( eyes, noses ,throat ) • weakens lung functions e.g. coughing, wheezing Effects on organic materials • deteriorates rubber ------ worn out easily • deteriorates fabrics ------ lower tensile strength

32. Acid Rain • Unpolluted rain water is slightly acidic, with a pH about 5.7. • This is because rain water reacts with CO2 in the air to form H2CO3. • Rain water with pH values lower than 5.7 is called acid rain.

33. Formation of acid rain • Acid rain is formed when air pollutants such as SO2 and NO2 dissolved in rain water. • SO2 + H2O  H2SO3 • 2NO2 + H2O → HNO3 + HNO2

34. Harmful effects of acid rain • Soil become too acidic for plants to grow. Forest are seriously damaged. • River and lakes become more acidic. Some aquatic plants and animals may die. • The corrosion of metal will be speeded up. • Damages building materials e.g. limestone and marble. All these materials contain CaCO3 which reacts with acid.

35. Controlling of acid rain • Reducing pollution from motor vehicles and industries. • Neutralizing the acid s in soil and water using lime. • Burning less fossil fuels.

36. Methods of minimizing pollutants from the burning fuels • A. Motor vehicles 1. Fitting catalyst converters to motor vehicles. 2. Using unleaded petrol. -- lead emission into the air can be greatly reduced. 3. Using LPG instead of diesel. -- it is much cleaner fuel than diesel. 4. Using alcohol instead of petrol. -- it is much cleaner fuel than petrol.

37. Catalytic Converter • Fitting a catalytic converter to the exhaust pipes of motor vehicles. • A catalytic converter is a stainless steel cylinder containing a honeycomb structure coated with platinum as catalyst. • Since the catalyst is easily poisoned by lead, it can only work efficiently on unleaded petrol.

38. Catalytic Converter • In the first half of the catalytic converter, poisonous gases, CO and NO react catalytically to form harmless CO2 andN2. 2CO(g) + 2NO(g) 2CO2(g) + N2(g) • In the second half of the converter, hydrocarbons and any remaining CO are oxidized to CO2 and H2O. 2CO(g) + O2(g)  2CO2(g) CxHy(l) + (x + y/4) O2(g)  xCO2(g) + y/2 H2O(l)

39. B. Factories 1. Using cleaner fuels with low sulphur content e.g. diesel fuel 2. Using scrubber -- Acidic sulphur oxide can be removed by reacting with alkalis to form sulphites or sulphates. 3. Using electrostatic precipitators -- Unburned small solid particles can be removed by this method.

40. Scrubber • A) Dry Scrubber Powdered limestone is added to the hot gases from burning coal. The heat decomposes the limestone to give lime. CaCO3(s)  CaO(s) + CO2(g) The lime then react with sulphur dioxide to give calcium sulphite. CaO(s) + SO2(g)  CaSO3(g) The calcium sulphite reacts with air to give calcium sulphate. 2CaSO3(s) + O2(g)  2CaSO4(g)

41. Electrostatic Precipitators • The solid particles in the smoke becomes negatively charged when passing through a high voltage electric field. • The negatively charged particles then attracted to the positive electrodes and stick to the sides of the precipitator. • The particles are then shaken to the bottom by the continuous knocking of a steel hammer. • Electrostatic Precipitator are usually used in incinerators and power stations.