Chapter 20 : Atmosphere and Environment
Name: _________________________ ( ) Class: _____ Date: ____________
What you will learn in this chapter:
(a) describe the volume composition of gases present in dry air as being approximately 79%
nitrogen, 20% oxygen and the remainder being noble gases (with argon as the main
constituent) and carbon dioxide
(b) name some common atmospheric pollutants, e.g. carbon monoxide; methane; nitrogen
oxides (NO and NO2); ozone; sulfur dioxide; unburned hydrocarbons
(c) state the sources of these pollutants as
(i) carbon monoxide from incomplete combustion of carbon-containing substances
(ii) nitrogen oxides from lightning activity and internal combustion engines
(iii) sulfur dioxide from volcanoes and combustion of fossil fuels
(d) describe the reactions used in possible solutions to the problems arising from some of the
pollutants named in (b)
(i) the redox reactions in catalytic converters to remove combustion pollutants
(ii) the use of calcium carbonate to reduce the effect of ‘acid rain’ and in flue gas
(e) discuss some of the effects of these pollutants on health and on the environment
(i) the poisonous nature of carbon monoxide
(ii) the role of nitrogen dioxide and sulfur dioxide in the formation of ‘acid rain’ and its
effects on respiration and buildings
(f) discuss the importance of the ozone layer and the problems involved with the depletion of
ozone by reaction with chlorine containing compounds, chlorofluorocarbons (CFCs)
(g) describe the carbon cycle in simple terms, to include
(i) the processes of combustion, respiration and photosynthesis
(ii) how the carbon cycle regulates the amount of carbon dioxide in the atmosphere
(h) state that carbon dioxide and methane are greenhouse gases and may contribute to global
warming, give the sources of these gases and discuss the possible consequences of an increase
in global warming
1. Composition of Air
Gas Composition by volume
Separation of Air into its components
- Air is first cooled and compressed into liquid.
- Liquid air is then separated into its constituents (or fractions) by
2. Air Pollution
Air pollution is defined as the condition in which air contains __________________
Common air pollutants:
Pollutants Major Sources Harmful Effects
(a) Carbon - Carbon monoxide reacts with
monoxide __________________________ of carbon- _______________ in the
containing substances blood to form
eg. charcoal, wood, petrol, etc.
__________________ so the
haemoglobin cannot transport
blood to the rest of the body.
- Cause headaches, fatigue,
or even death
1) Reactions that occur in car engines (
(b) ___________________________________) 1)
__________ 2) From __________________
(eg. nitrogen Nitrogen reacts with oxygen in the air to form
monoxide, 3) Lung inflammation
N2 (g) + O2 (g) 2NO (g)
NO & (bronchitis)
nitrogen Nitrogen monoxide reacts with oxygen to form
dioxide, nitrogen dioxide (NO2). 4) Acid rain
NO2.) 2NO (g) + O2 (g) 2NO2 (g)
(c) Sulfur 1) __________________________________
dioxide _______________________ (especially coal)
Sulfur reacts with oxygen in the air to form
S (g) + O2 (g) 2SO2 (g)
3. Other air pollutants
(a) ________________________ (b) ___________________________
• _________________________ are released in car exhaust.
• _____________________ is a colourless and odourless gas produced when plant
and animal matter decay. It is also produced from the decay of rubbish in
4. Effects of Air Pollution – Acid Rain
• Rain usually has a pH that is slightly below 7.
• Why? ________________________________________________________
• However, acid rain has a pH value of 4 or less.
(a) Formation of acid rain
gases react with air
and water in clouds
sulphuric acid nitric acid gases damage
coal, oil, fossil
fuels burned soils acid damages
acidified trees through
acid kills roots
• Acid rain is formed when acidic air pollutants such as
__________________(SO2) and ___________________________ (NO2)
dissolve in rainwater.
• Sulfur dioxide dissolves in water to form ________________________
In the presence of oxygen in the air, acid is slowly oxidised to sulphuric acid
• In the presence of oxygen and water, nitrogen dioxide is converted to ________.
(b) Effects of Acid Rain
• ______________________________________ such as fences and bridges
• Reacts with ______________________ in marble and limestone.
• ______________________ value of natural water bodies to below 4, which will
• _______________________________ from the soil and destroys plants.
(c) Reducing effects of Acid Rain
(i) Catalytic converters
o Attached to the exhaust system of a car.
o Contains catalysts - platinum and rhodium.
o Catalytic converters involve the use of __________________________
to remove air pollutants:
__________________________ is oxidised to carbon dioxide.
___________________________ are reduced to nitrogen.
Eg. Nitrogen monoxide + carbon monoxide nitrogen + carbon dioxide
Chemical equation: ________________________________________
______________________________________ are oxidised to
carbon dioxide and water.
Eg. Octane + oxygen carbon dioxide + water vapour
2 C8H18 (g) + 25 O2 16 CO2 (g) + 18 H2O (g)
(ii) Flue Gas Desulfurisation
2 ways of minimising the effects of sulphur dioxide pollution:
• _____________________ from fossil fuels before burning. However, this
method is too expensive and difficult.
• Remove ___________________ from _____________(flue gases) from
- Process known as desulfurisation
o Sulfur dioxide reacts with an aqueous suspension of _________________
to form solid ______________________________.
CaCO3(s) + SO2(g) CaSO3(s) + CO2(g)
o The calcium sulfite is further oxidised to _________________________
by atmospheric oxygen.
CaSO3(s) + O2(g) 2CaSO4(s)
5. Control of Air Pollution in Singapore
• __________________ of the use of open __________for the disposal of
domestic and industrial wastes
• Introduction of _____________________ and phasing out of leaded petrol
• ________________ of the permissible level of ______________ in diesel
• Fitting of all petrol-driven vehicles with ___________________________
6. Depletion of the Ozone Layer
• Ozone is a bluish, very reactive gas, whose molecule is made by
• At low altitudes, it can cause breathing difficulties and photochemical smog.
• However, in the stratosphere, the ozone layer shields us from
Note: UV radiation can cause skin cancer, genetic mutations and cataracts.
• What is causing the depletion of ozone in the stratosphere?
Note: CFCs are compounds containing the elements carbon, fluorine & chlorine.
They are widely used as ________________________________________
and as _________________________ in refrigerators and air conditioners.
• How do CFCs destroy the ozone layer?
- Propellants in aerosols and coolants from refrigerators release
______________ into the atmosphere.
- CFCs reach the stratosphere where the protective layer is found.
- In the presence of sunlight, CFCs decompose to form ________________.
- Chlorine atoms react with __________ molecules in the stratosphere to
form ____________________________, thus destroying the ozone
• What is being done to the problem of ozone depletion?
7. The Carbon Cycle
is called the carbon cycle.
• Processes that produce carbon dioxide:
(a) ______________________: During respiration, carbon and hydrogen
compounds in food are converted into ______________ and
C6H12O6(aq) + 6O2(g) 6CO2(g) + 6H2O(l) + energy
Most fuels contain both carbon and hydrogen. When these fuels are burnt,
_____________________ and ________________are produced.
CH4(g) + 2O2(g) CO2(g) + 2H2O(l)
Heat energy is also given off.
• Processes that remove carbon dioxide
During photosynthesis, green plants convert carbon dioxide and water into
glucose and oxygen in the presence of sunlight.
6CO2(g) + 6H2O(l) C6H12O6(aq) + 6O2(g)
8. (a) The Greenhouse Effect
• Greenhouse gases allow the visible radiation from the sun to reach the Earth’s
surface but ___________________________________________ which is
emitted by the Earth. This produces a _______________________ called
the greenhouse effect.
• Carbon dioxide is one of the main greenhouse gases. Besides carbon dioxide,
what are the other types of greenhouse gases?
8. (b) Global warming
• Greenhouse gases, such as carbon dioxide, are building up rapidly in the
atmosphere. Why is that so? _____________________________________
• Therefore, carbon dioxide is being added to the atmosphere at a higher rate
than photosynthesis can remove the excess gas.
• The effect of carbon dioxide build-up is an ________________________
____________________________________________ global warming
• Consequences of Global warming.
o a __________________________ world-wide because the areas that
are currently covered by vegetation may become deserts,
o the ______________________________________ in the North Pole
and South Pole. This will cause the levels of oceans to rise and _______
low-lying countries such as the Netherlands.
o the ____________________________ from the Earth’s surface.
When this happens, carbon dioxide dissolved in the oceans will be driven
out into the atmosphere. This adds further to the greenhouse effect.
What questions do you have?