Air Pollution: Sources, Effects, Prevention and Control

Air Pollution-It is an undesirable change in the physical, chemical or biological characteristics of air.

Air Pollutants-They are the substances which pollute the air. Some of the common pollutants are dust, soot, ash, carbon monoxide, excess of carbon dioxide, sulphur dioxide, oxides of nitrogen, hydrocarbons, chlorofluorocarbons(CFC), lead compounds, asbestos dust, cement dust, pollens and radioactive rays.

The pollution of air can be caused by natural processes or by human activities.

• The sources of air pollution are classified into two groups:

1. Natural Sources
2. Man made sources

Natural Sources of Air Pollution-They are dust storms, forest fires, ash from smoking volcanoes, decay of organic matters and pollen grains floating in air.

Manmade Sources of Air Pollution-They are population explosion, deforestation, urbanisation and industrialisation, whose effects can be explained as follows:

1. Burning of fuels like wood, cow dung cakes, coal and kerosene in homes pollute the air.
2. Exhaust gases emitted by motor vehicles which pollute the air are the major source of air pollution in big cities.
3. Industries pollute air by releasing various types of pollutants such as sulphur dioxide, oxides of carbon, nitrogen oxide, chlorine, asbestos dust and cement dust.
4. Thermal power plants pollute air by emitting sulphur dioxide and fly-ash.
5. Nuclear power plants pollute air by releasing radioactive rays.
6. Use of fertilisers and pesticides in agriculture pollute the air.
7. Mining activities releases particulate matter into the air and pollutes it.
8. Indiscriminate cutting of trees and clearing of forests increases the amount of carbon dioxide in the atmosphere and thereby pollutes it.
9. Use of chlorofluorocarbons in refrigeration, fire extinguishers and aerosol sprayers pollutes air by depleting the ozone layer.
10. Smoking pollutes air by emitting carbon monoxide and nicotine.

1. Air pollution affects respiratory system causing breathing difficulties and diseases such as bronchitis, asthma, lung cancer, tuberculosis and pneumonia.
2. It affects the central nervous system causing carbon monoxide poisoning. CO has more affinity for haemoglobin than oxygen and thus forms a stable compound carboxy haemoglobin(COHb), which is poisonous and causes suffocation and death.
3. It causes depletion of ozone layer due to which ultraviolet radiations can reach the earth and cause skin cancer, damage to eyes and immune system.
4. It causes acid rain which damages crop plants, trees, buildings, monuments, statues and metal structures and also makes the soil acidic.
5. It causes greenhouse effect and global warming which leads to excessive heating of earth's atmosphere, further leading to weather variability and rise in sea level. The increased temperature may cause melting of ice caps and glaciers, resulting in floods.
6. Air pollution from certain metals, pesticides and fungicides causes serious ailments.

• Lead pollution causes anaemia, brain damage, convulsions and death.
• Certain metals cause problem in kidney, liver, circulatory system and nervous system.
• Fungicides cause nerve damage and death.
• Pesticides like DDT(Dichloro diphenyl trichloroethane) which are toxic enter into our food chain and gets accumulated in the body causing kidney disorders and problems of brain and circulatory system.

Different techniques are used for controlling air pollution caused by 'gaseous pollutants' and that caused by 'particulate pollutants'.

• Methods of controlling gaseous pollutants-The air pollution caused by gaseous pollutants like hydrocarbons, sulphur dioxide, ammonia, carbon monoxide, etc can be controlled by using three different methods-Combustion, Absorption and Adsorption.

1. Combustion-This technique is applied when the pollutants are organic gases or vapours. The organic air pollutants are subjected to 'flame combustion or catalytic combustion' when they are converted to less harmful product carbon dioxide and a harmless product water.
2. Absorption-In this method, the polluted air containing gaseous pollutants is passed through a scrubber containing a suitable liquid absorbent. The liquid absorbs the harmful gaseous pollutants present in air.
3. Adsorption-In this method, the polluted air is passed through porous solid adsorbents kept in suitable containers. The gaseous pollutants are adsorbed at the surface of the porous solid and clean air passes through.

• Methods of controlling particulate emissions-The air pollution caused by particulate matter like dust, soot, ash, etc can be controlled by using fabric filters, wet scrubbers, electrostatic precipitators and certain mechanical devices.

1. Mechanical Devices-It works on the basis of following:

• Gravity-In this process, the particulate settle down by the action of gravitational force and get removed.
• Sudden change in the direction of air flow-It brings about separation of particles due to greater momentum.

2. Fabric Filters-The particulate matter is passed through a porous medium made of woven or filled fabrics.

• The particulate present in the polluted air are filtered and gets collected in the fabric filters, while the gases are discharged.
• The process of controlling air pollution by using fabric filters is called 'bag filtration'.

3. Wet Scrubbers-They are used to trap SO₂, NH₃ and metal fumes by passing the fumes through water.

4. Electrostatic Precipitators-When the polluted air containing particulate pollutants is passed through an electrostatic precipitator, it induces electric charge on the particles and then the aerosol particles get precipitated on the electrodes.

Some other methods of controlling Air Pollution:

1. Tall chimneys should be installed in factories.
2. Better designed equipment and smokeless fuels should be used in homes and industries.
3. Renewable and non-polluting sources of energy like solar energy, wind energy, etc should be used.
4. Automobiles should be properly maintained and adhere to emission control standards.
5. More trees should be planted along roadsides and houses.