1. Air Pollution
Chapter 44A

2. Pollution
Pollution is the release of waste matter or energy into the environment by man so that it causes damage or deterioration to living systems and/or environment.
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3. Pollutants
NO2
C6H6 CO
C particles
A pollutant is any substance brought about by human activities or source of energy which, at an unacceptable level, causes damage to the environment or is harmful to living systems.

4. Some air pollutants Carbon monoxide Sulphur dioxide Nitrogen oxides
Hydrocarbons
Ozone
Particulates

5. Carbon monoxide A poisonous gas, can cause death.
Combines with haemoglobin in red blood cells to form stable complex, carboxyhaemoglobin.
The haemoglobin is NOT available for carrying oxygen. May cause death.

6. Sulphur Dioxide
Causes damage to respiratory systems and increase in asthma attacks(哮喘).
Acid rain – damage buildings, thought to be responsible for the deaths of large numbers of trees in Europe and America.

7. Nitrogen oxides
A poisonous gas that damage lung tissues and blood vessels.
Acid rain
Give rise to photochemical smog.

8. Hydrocarbons Cause photochemical smog.
Some hydrocarbons, e.g. benzene, are known carcinogens.

9. Ozone
Irritates the eyes.
Makes more serious asthma.
Damages plants.

10. Particulates
Impair lung function by constricting respiratory passage and damaging lung tissue, cause respiratory disease.
Certain particles are suspected to cause cancer.

11. Harmful effect Concentration (ppm) Duration of exposure CO
4000 ppm or higher cause death in 1 hour ( or 1000 ppm for 4 hours)

12. Concentrations
ppm = number of molecules of pollutants per million (106) molecules of air
% by volume
Microgram per cubic metre ( g m-3)

13. Concentrations Convert 0.05 ppm of CO into other concentration units
% volume
g m-3

14. Answers a. 0.000005% In 1 m3 , there is 0.05/106 m3 of CO
Using Ideal gas equation,
m = pVMr / RT
Mass of CO = 101x103 x 0.05 x 10-6 x 28 / 8.31 x 298
= 5.71 x g = g
Thus, the concentration = g/m3

15. Acid rain Normal rainwater pH = 6.5
pH 2.5 has been recorded in some parts of the world
SO2 + H2O  H2SO3
SO2 + O2  SO3  H2SO4
4NO2 + 2H2O + O2  4HNO3

16. Effect of acid rain
pH < 4.5, calcium metabolism in fresh water fish will be affected, poor health and growth.
Soil of pH < 4.5, absorption of cations by plants will be affected, death of plants.
Corrodes metals and accelerates the deterioration of building, rock and statue.

17. Photochemical smog NO2  NO + O (under U.V. light) O + O2 + M  O3 + M
O + hydrocarbons  aldehydes
O3 + hydrocarbons  aldehydes
Hydrocarbons + O2 + NO2  CH3- C-O-O-NO2 (PAN molecule) O

18. Photochemical smog Smoke + Fog (Brownish haze)
Reaction initiated by sunlight + NOx + hydrocarbons
Effects:
1. Cause headaches, eye, nose and
throat irritations.
2. Impair lung function, coughing.
3. Cause rubber and fabrics to deteriorate.
4. Damage plants, loss of crops.

19. Sources and properties of Ozone
In lower part of atmosphere
NO2  NO + O (under UV light)
O + O2  O3
From air by electric sparks in engines, photocopiers, motors.
Lightning
Too reactive to remain for a long time
Adverse effect on health

20. Desirability of ozone
Stratosphere (20 –50 km above earth’s surface), filter out 99% dangerous UV:
Create:
O2 + uv light (250 nm)  2 O•
O• + O2 + M  O3 + M
Destroy:
O3 + uv light ( nm)  O2 + O•
O• + O3  2O2

21. Depletion of the ozone layer
OO=O
Ozone Hole

22. Chlorofluorocarbons (CFCs)
Unreactive , low flammability and toxicity.
Use as : Aerosol propellants, solvents, refrigerants, blowing agents in foam plastic.
Causes for accumulation:
Unreactive, lifetime about 75 years
Insoluble in water

23. Depletion of ozone layer
CFCs give Cl free radicals which destroy ozone.
CCl3F+uv light  CCl2F. + Cl.
Cl. + O3  ClO. + O2 (1)
ClO. + O  Cl. + O2 (2)
Repeat (1) (2)
Step (1) is considerably faster than O + O3  2O2
Disturb the balance in the production and destruction of ozone.

24. Adverse effect of ozone depletion
Reduced crop yield
Higher incidence of skin cancer and eye cataract

25. Control of the ozone depletion problem
Control the production and consumption of CFCs (Montreal Protocol)
Recycling of CFCs
Using substitutes

26. Possible alternatives for CFCs
Hydrochlorofluorocarbons (HCFCs) such as CF3CHCl2 , they break down more quickly in atmosphere, though lower % of Cl, could damage if overused.
Hydrofluorocarbons (HFCs) such as CF3CH2F, no chlorine and ‘ozone safe’, toxicity problem still unsolved.

27. Possible alternatives for CFCs
Hydrocarbons such as butane and propane, no chlorine, flammable and poisonous.
Water and steam, effective for some cleaning applications.

28. Pollution control in H.K.
Environmental protection department (EPD), established 1986
Formulating policy
Monitoring
Enforcing legislation
Planning
Handling complaints and enquiries

29. Measures to improve air quality
Use of unleaded petrol
Installation of catalytic converters in car
Limitation of sulphur content in fuel
Desulphurization of Flue Gas
Installation of Electrostatic Precipitators in power plants
Low nitrogen oxide burners

30. Web page
Environmental Protection Department

31. Past AL papers Ozone depletion (1998 5b) Catalytic converter (1998 6b)
SO2, ppm calculation (1999 6d)
SO2 (2000 5a)
Smog (2000 5b)
CFC (2001 6a)