Chapter 23Air

LEARNING OUTCOMESLesson 2

Describe the causes of air pollution and sources of the following air pollutants: SO2, CO, NO, NO2, CH4, O3 and unburned hydrocarbons. Describe the harmful effects of these air pollutants on health and the environment.

Air Pollution

The air we breathe in may not be clean. It may be polluted by substances called pollutants.

Pollutants are harmful substances that have undesirable effects on people and the environment.

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Air Pollution The main air pollutants are:

► Carbon monoxide ( CO )

► Sulphur dioxide (SO2)

► Nitrogen oxides (NO, NO2)

► Chlorofluoro carbons (CFCs)

► Methane (CH4)

► Ozone (O3) at ground level

► Unburned hydrocarbons

Chapter 23Air

Carbon monoxide (CO) Carbon monoxide comes from forest fires, incomplete

combustion of fuels in motor vehicles, factories and power stations.

Carbon monoxide reacts with the haemoglobin in the red blood cells making them unable to absorb oxygen. Small quantities of carbon monoxide cause headaches and breathing difficulties, larger quantities cause heart damage and death.

Carbon monoxide is dangerous as it is colourless and odourless and thus gives no warning of its presence.

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Sulphur dioxide (SO2) Sulphur dioxide comes from the burning of fuels like

coal and fuel oil in factories and power stations. When these fuels burn, the sulphur in the fuel is

oxidised into sulphur dioxide: S + O2 SO2

Some sulphur dioxide comes from volcanic eruptions. Sulphur dioxide causes eye irritation, breathing difficulties and asthma attacks. Sulphur dioxide causes the formation of acid rain.

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Nitrogen oxides (NOx) Nitrogen monoxide is produced when nitrogen combines

with oxygen at high temperature, such as during lightning storms and inside the engines of motorcars.

N2 + O2 2NO The nitrogen monoxide then combines with more oxygen to form nitrogen dioxide: 2NO + O2 2NO2 Nitrogen oxides cause breathing difficulties and lung damage. Nitrogen oxides react with unburned hydrocarbons to form ground level ozone and photochemical smog.

Nitrogen dioxide reacts with atmospheric oxygen and water to form acid rain.

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Chlorofluoro carbons (CFCs) Most of these compounds are used as solvents, coolant gases in refrigerators and

for making plastics. CFCs destroy the ozone layer that

protects our earth from ultra violetradiations from the sun.

Pollution from CFCs can bereduced by banning their use inaerosol sprays and refrigerators.

Hole in ozone layer

Chapter 23Air

Methane Small amounts of methane are present naturally in the atmosphere due to the decay of vegetation and

animals. However, increasingly large amounts

of methane are produced because ofagriculture, mining activities andrearing of animals such as cows.

Methane causes the “greenhouse effect” which traps the sun’s heat and causes global warming, leading to drastic climatic changes and melting of the polar ice caps.

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Ozone A layer of ozone surrounds the earth at high attitude and protects us from the harmful radiations of the sun.

However, at ground level, ozone is aharmful pollutant that causes irritationto the eyes and throats. It also causesbreathing difficulties and asthma attacks.

Most of the ozone is produced by the action of sunlight on nitrogen dioxide and unburned hydrocarbons. In heavily polluted cities it forms photochemical smog.

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Carbon dioxide Carbon dioxide occurs naturally in the air to about 0.03% and is used by

plants for photosynthesis. Oxygen is released during photosynthesis, and so there is a balance in nature which maintains the amounts of carbon dioxide and oxygen in the atmosphere.

However, the level of carbon dioxide has been increasing rapidly over the last 50 years due to industrialisation and urbanisation which resulted in the accelerated burning of fossil fuels and clearing of forests.

Carbon dioxide is a greenhouse gas which contributes to globalwarming. Global warming leads to drastic weather changes, such as extreme

droughts in some parts and heavy rain in other parts of the world. Global warming has caused the melting of the polar ice caps and will eventually cause flooding to many coastal regions of the world.

A battered Earth

Chapter 23Air

Quick check 2

Solution

1. Name two air pollutants that are (a) non-acidic,(b) acidic.

2. Name the air pollutants that are released into the atmosphere by the following: (a) volcanic eruptions, (b) decay of vegetation, (c) forest fires, (d) motorcars.

3. (a) What is the formula of ozone? (b) How is ozone useful and also a pollutant? (c) Describe how ground level ozone is produced.

Chapter 23Air

1. (a) Non-acidic: ozone, methane; (b) Acidic pollutants: sulphur dioxide, nitrogen dioxide.

2. (a) volcanic eruptions: sulphur dioxide, (b) decay of vegetation: methane, (c) forest fires: carbon monoxide, carbon dioxide, (d) motorcars: carbon monoxide, nitrogen oxides, unburned hydrocarbons, carbon dioxide.

3. (a) Formula of ozone: O3 (b) Ozone is useful when it is high in the upper atmosphere where it protects the earth against the harmful UV radiations from the sun. At ground level ozone is harmful because it causes irritations to the eyes and throat and harms the lungs. (c) Ground level ozone is produced when nitrogen oxides react with unburned hydrocarbons under strong sunlight.

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Chapter 23Air

Solution to Quick check 2