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1. Chapter
22
Air

2. contents
You will learn about:
• air pollutants, its sources and
effects
• The ozone hole
• Global warming

3. air pollution
Air around us contains pollutants,
which are harmful substances to the
environment
Harmful Treatment or
Pollutants Major Sources
Effects Prevention
supply excess air to
headaches;
ensure complete
carbon incomplete combustion breathing
combustion; fit
monoxide of carbon fuels difficulties; can
vehicles with
kill people
catalytic converters
bacterial decay of
methane vegetation; farm global warming no easy solutions
animals and rice growing
breathing
difficulties;
oxides of lightning; vehicle fit vehicles with
acid rain;
nitrogen engines catalytic converters
produces
ozone

4. air pollution
Harmful Treatment or
Pollutants Major Sources
Effects Prevention
sunlight acting on irritates eyes reduce vehicle
ozone unburnt hydrocarbons and lungs; emissions of
and nitrogen dioxide asthma attacks pollutants
breathing burn less sulphur-
combustion of fossil difficulties; containing fuels;
sulphur
fuels – especially coal; asthma absorb SO2 from
dioxide
volcanoes’ eruptions attacks; acid chimney gases with
rain calcium carbonate
unburnt produces fit vehicles with
vehicle engines
hydrocarbons ozone catalytic converters

5. air pollution
carbon monoxide (CO)
 colourless and odourless gas
 comes from the incomplete combustion of fuel in vehicles;
all new motor cars in Singapore are fitted with catalytic
converters; oxidises CO to CO2
 can be absorbed by haemoglobin
in the blood, thus blood can no
longer absorb O2
 extra amounts of CO result in
tiredness, headaches, heart
damage and small amounts can
be lethal

6. air pollution
sulphur dioxide (SO2)
 fuels (coal and petroleum) contain sulphur as an impurity;
when fuels are burnt, sulphur is oxidised to SO2
 is also emitted from volcanoes’
eruptions
 irritates the eyes and causes breathing
difficulties; main cause of acid rain
 in Singapore, there are measures to
reduce the emission of SO2 into the
atmosphere:
o oil fuels are not allowed to contain
more than 2% sulphur
o exhaust gases from power stations
and industries are treated with
CaCO3 to remove acidic SO2
volcanoes: natural
source of SO2 pollution

7. air pollution
nitrogen oxides (NO and NO2)
 oxides of nitrogen (NO and NO2) are produced naturally in
lightning and forest fires
 excess man-made production of oxides of nitrogen is
harmful; found inside motorcar engines, power stations
and industries
 damage people’s lungs and react with other pollutants to
form ozone
 preventive measure: motorcars are fitted with catalytic
converters to reduce oxides of nitrogen to N2

8. air pollution
acid rain
gases react with air
and water in clouds
sulphuric acid nitric acid
gases damage
ACID RAIN green leaves
acid corrodes
buildings and
metal structures
coal, oil, fossil lakes
fuels burned soils acidified
acidified acid damages
acid kills trees through
fish roots

9. air pollution
acid rain
 sulphur dioxide (SO2) and nitrogen dioxide (NO2) are
acidic oxides that react with oxygen and water vapour in
the air to form sulphuric acid and nitric acid which become
acid rain
SO2 + oxygen + water vapour sulphuric acid
NO2 + oxygen + water vapour nitric acid
acidic atmosphere acid rain
oxides
 typical pH of acid rain is 4 which is 1000 times more
acidic than clean water

10. air pollution
acid rain
 harmful effects:
o corrodes the cement and stones used in buildings
o corrodes the steel structures such as fences and bridges
o kills fishes in fresh water lakes
o makes agricultural land acidic thus crops grow poorly
damage to left statue
caused by acid rain

11. air pollution
acid rain
 prevention:
o burn fuels that contain less sulphur
o neutralise acidic oxides from power stations with alkalis
before they are released into the atmosphere
o fit motor cars with catalytic converters to reduce the
emission of nitrogen oxides
o adding calcium hydroxide to lakes and soils to neutralise
the acid

12. air pollution
ozone and hydrocarbons
 ozone, O3, at ground level is a nasty pollutant
 irritates people’s eyes, chests and throats and causes
breathing difficulties
 produced by the action of sunlight on pollutants such as
NO2 and hydrocarbons; formation of a ‘photochemical
smog’
 preventive measure: reduce the emissions of unburnt
hydrocarbon fuels
sunlight reacting with unburnt
hydrocarbons from vehicle exhausts
causing formation of ozone

13. air pollution
pollution from motor vehicles
 exhaust gases from a motorcar engine consist of CO2, CO,
hydrocarbons, H2, nitrogen oxides, lead compounds and
other non-polluting gases
 measures have been taken to reduce this pollution:
o introduction of lead-free petrol (Singapore stopped
using leaded petrol in 1998)
o oxygen sensor and modified distributor are used to
ensure more complete combustion
o catalytic converters are fitted in cars to remove the
pollutants

14. air pollution
methane (CH4)
 small amounts of methane are naturally present in the
atmosphere; bacterial decay of vegetation and other
sources
 increasing amount of
methane in recent
years observed;
human activities such
as agriculture, mining
and waste disposal
 methane (heat-
trapping gas) causes
‘greenhouse effect’ /
global warming
rice fields are a major source of methane

15. the ozone hole
chlorofluorocarbons (CFCs)
 are compounds of carbon, chlorine and fluorine; gases at
room conditions; liquids under a small pressure
 examples of CFCs: CFCl3 and CF2Cl2
model of a CFC molecule,
CFCl3

16. the ozone hole
chlorofluorocarbons (CFCs)
 are chemically unreactive and do not burn
 uses of CFCs:
o aerosol propellants
o coolant fluids for refrigerators
and air conditioners
o good solvents to clean grease
from silicon chips
 CFCs molecules rise up into
the atmosphere and are
decomposed by sunlight to
produce chlorine atoms aerosol cans and
foam plastic are
sources of CFCs

17. the ozone hole
the ozone hole
 the Earth is protected by a layer of ozone about 40km
above the ground
 this layer of ozone absorbs harmful ultraviolet(UV)
radiation from the Sun
harmful UV radiation
from the Sun
ozone hole
ozone layer
South Pole
Antarctica

18. the ozone hole
the ozone hole
 chlorine atoms from CFCs destroy the ozone molecules;
amount of ozone in the ozone layer decreases
 formation of the ozone hole; dangerous UV radiation
streamed through the hole
 causes skin cancer an damage to vegetation
 use of CFCs is phased out to protect the ozone layer

19. global warming
the carbon cycle
 shows the movement of carbon
 0.03% of the atmosphere is CO2
 CO2 in the air is continually being removed by green
plants in photosynthesis; it is then replaced by other
processes (e.g. combustion and respiration)
 this two-way process has been in balance over the past
few millennia; amount of CO2 in the atmosphere remained
fairly constant
 however, with global industrialisation and increased use of
fossil fuels, amount of CO2 in the atmosphere increases;
resulting in global warming

20. global warming
the carbon cycle
Carbon dioxide in the air
combustion
hea
t an
da
cid
r ain
Fossil fuels Carbon dioxide
(coal, petroleum, Limestone chalk
in the sea
death, decay and respiration
natural gas)
death and decay
photosynthesis
decay and
pressure
over millions Sea shells
of years
eating
Plants Animals

21. global warming
global warming
 global warming is largely caused by increasing CO2 and
other heat trapping gases (e.g. methane) in the
atmosphere
 large amount of heat trapped on Earth; Earth becomes
hotter
carbon dioxide and
some radiation from methane trap radiation by
the Sun radiated back reflecting it back to Earth
into space
radiation from the
Sun reaches the
Earth’s surface
vehicles
rice fields and
decaying vegetation factories and
mining power station

22. global warming
global warming
 results in rise in sea levels, flooding of low-lying lands,
melting of polar ice caps and changes in global climate
 measures to reduce use of fossil fuels (to reduce CO2
emission):
o use tidal, wind and hydroelectric energy to generate
electricity
o use of solar energy

23. combustion of
photosynthesis carbon fuels
nitrogen
and respiration
removed
argon and from air by added to
oxygen other gases global
inc air by
lud warming
es
by
CO2
se d
contains excess of is
cau
contains is
air pollutants methane
are are is
are
sulphur are
carbon
dioxide des are
monoxide
unburnt
CFCs troy
nitrogen hydrocarbons ing
c au
protective
aus
oxides is
se
e
ozone layer
cau causes
se
petrolchemical
acid rain ozone
smog