Air Pollution

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Air Pollution

• Chapter 44A

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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.

Photo from National Geographic Society -
Exploring your world
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Pollutants

• 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.

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Some air pollutants

• Carbon monoxide
• Sulphur dioxide
• Nitrogen oxides
• Hydrocarbons
• Ozone
• Particulates

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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.

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Sulphur Dioxide

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

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Nitrogen oxides

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

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Hydrocarbons

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

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Ozone

• Irritates the eyes.
• Makes more serious asthma.
• Damages plants.

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Particulates

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

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Harmful effect

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

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Concentrations

• ppm number of molecules of pollutants per
  million (106) molecules of air
• by volume
• Microgram per cubic metre ( ?g m-3)

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Concentrations

• Convert 0.05 ppm of CO into other
  concentration units
• volume
• ?g m-3

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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 10-7 g
  57.1 ?g
• Thus, the concentration 57.1 ?g/m3

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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

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Effect of acid rain

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

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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

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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.

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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

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Desirability of ozone

• Stratosphere (20 50 km above earths surface),
  filter out 99 dangerous UV
• Create
• O2 uv light (250 nm) ? 2 O
• O O2 M ? O3 M
• Destroy
• O3 uv light (215-295 nm) ? O2 O
• O O3 ? 2O2

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Depletion of the ozone layer
Ozone O?OO
Ozone Hole
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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

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Depletion of ozone layer

• CFCs give Cl free radicals which destroy ozone.
• CCl3Fuv 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.

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Adverse effect of ozone depletion

• Reduced crop yield
• Higher incidence of skin cancer and eye cataract

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Control of the ozone depletion problem

• Control the production and consumption of CFCs
  (Montreal Protocol)
• Recycling of CFCs
• Using substitutes

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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.

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Possible alternatives for CFCs

• Hydrocarbons such as butane and propane, no
  chlorine, flammable and poisonous.
• Water and steam, effective for some cleaning
  applications.

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Pollution control in H.K.

• Environmental protection department (EPD),
  established 1986
• Formulating policy
• Monitoring
• Enforcing legislation
• Planning
• Handling complaints and enquiries

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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

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Web page

• Environmental Protection Department

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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)