Air Pollution

Air Pollution Chapter 44A

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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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.

CO NO2

C particles C6H6

Some air pollutants 

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Carbon monoxide Sulphur dioxide Nitrogen oxides Hydrocarbons Ozone Particulates

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.

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.

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

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

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

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

Harmful effect   

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

Concentrations 

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ppm = number of molecules of pollutants per million (106) molecules of air % by volume Microgram per cubic metre ( µg m3 )

Concentrations Convert 0.05 ppm of CO into other concentration units • ∀

% volume µg m-3

Answers a.

0.000005%

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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 µg Thus, the concentration =

57.1 µg/m3

Acid rain  

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Normal rainwater pH = 6.5 pH 2.5 has been recorded in some parts of the world SO2 + H2O → H2SO3

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SO2 + O2 → SO3 → H2SO4

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4NO2 + 2H2O + O2 → 4HNO3

Effect of acid rain 

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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.

Photochemical smog 

NO2 → NO + O (under U.V. light)

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O + O2 + M → O3 + M

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O + hydrocarbons → aldehydes O3 + hydrocarbons → aldehydes Hydrocarbons + O2 + NO2 → CH3- C-O-O-NO2 (PAN molecule) O

Photochemical smog 

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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.

Sources and properties of Ozone In lower part of atmosphere

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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

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 (215-295 nm) → O2 + O• O• + O3 → 2O2

Depletion of the ozone layer Ozone: O←O=O

Ozone Hole

Chlorofluorocarbons (CFCs) 

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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

Depletion of ozone layer 

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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.

Adverse effect of ozone depletion  

Reduced crop yield Higher incidence of skin cancer and eye cataract

Control of the ozone depletion problem 

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

Possible alternatives for CFCs 

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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.

Possible alternatives for CFCs 

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

Pollution control in H.K. 

Environmental protection department (EPD), established 1986     

Formulating policy Monitoring Enforcing legislation Planning Handling complaints and enquiries

Measures to improve air quality  

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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

Web page 

Environmental Protection Departmen

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)