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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.
Photo from National GeographicSociety - Exploring your world
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)