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.

NO2 C6H6

CO C particles

Some air pollutants Carbon monoxid

e 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 DioxideCauses 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 ppm = number of molecules of polluta

nts per million (106) molecules of air % by volume Microgram per cubic metre ( g m-3)

Concentrations

Convert 0.05 ppm of CO into other concentration units

a. % volume b. g m-3

b. 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

a. 0.000005%

Answers

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

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.

Photochemical smog NO2 NO + O (under U.V. light) O + O2 + M O3 + M O + hydrocarbons aldehydes O3 + hydrocarbons aldehydes Hydrocarbons + O2 + NO2 CH

3- C-O-O-NO2 (PAN molecule) O

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 deter

iorate. 4. Damage plants, loss of crops.

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

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 + MDestroy:O3 + uv light (215-295 nm) O2 + O•O• + O3 2O2

Depletion of the ozone layer

Ozone:

OO=O Ozone Hole

Chlorofluorocarbons (CFCs) Unreactive , low flammability and toxi

city. Use as : Aerosol propellants, solvents,

refrigerants, blowing agents in foam plastic.

Causes for accumulation:Unreactive, lifetime about 75 yearsInsoluble in water

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 2

O2 Disturb the balance in the production and des

truction of ozone.

Adverse effect of ozone depletion Reduced crop yield Higher incidence of skin

cancer and eye cataract

Control of the ozone depletion problem Control the production

and consumption of CFCs (Montreal Protocol)

Recycling of CFCs Using substitutes

Possible alternatives for CFCs Hydrochlorofluorocarbons (HCFCs) su

ch 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 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 Use of unleaded petrol Installation of catalytic converters in car Limitation of sulphur content in fuel Desulphurization of Flue Gas Installation of Electrostatic Precipitator

s in power plants Low nitrogen oxide burners

Web page Environmental Protection Departm

ent

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)