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Pollution is any undesirable change in physical, chemical or biological characteristics of air, land, water or soil.

Agents that bring about such an undesirable change are called as pollutants.

Environment (Protection) Act – In 1986, Government of India passed the act to protect and improve the quality of our environment (air, water and soil).

Air pollution: Any undesirable change in the quality of air, which can be due to pollutants like particulate matter, gases, dust, harmful fumes etc. is considered as air pollution. Also, Noise is considered as air pollutant.

• Harmful effects of Air pollution: 1. Reduce growth and yield of crops, 2 . Cause premature death of plants 3. Affect the respiratory system of humans and of animals.

Effects of air pollutants depend on the concentration of pollutants, duration of exposure and the organism.

Industrial Air pollution

There are two types to clean the dirty air released by thermal power plants, smelters and other industries. Smoke released from these contains particulate matter and gaseous air pollutants together with harmless gases, such as nitrogen, oxygen, etc. These pollutants must be separated/ filtered out before releasing the harmless gases into the atmosphere.

1)Electrostatic precipitator

• Electrostatic precipitators are used to remove particulate matter present in the exhaust of industries and thermal power plants. It is the most widely used method.
• These precipitators can remove over 99 per cent particulate matter present in exhaust.
• Electrostatic precipitator has electrode wires that are maintained at several thousand volts, which produce a corona that releases electrons. These electrons attach to dust particles giving them a net negative charge. The collecting plates are grounded and attract the charged dust particles. The velocity of air between the plates must be low enough to allow the dust to fall.

2) Scrubber

• It can remove gases like sulphur dioxide.
• In a scrubber, exhaust is passed through a spray of water or lime.

Scrubber and Electrostatic precipitator

Particulate matter (PM) 2.5: According to Central Pollution Control Board (CPCB), these methods to clean industrial exhaust are not sufficient to clean particulate size 2.5 micrometers or less in diameter (PM 2.5). PM 2.5 if inhaled can reach deep into the lungs and can cause breathing and respiratory symptoms, irritation, inflammations and damage to the lungs and premature deaths.

Vehicular Air Pollution

Automobiles are also a major cause for atmospheric pollution. Use of lead-free petrol or diesel can reduce the pollutants they emit. Catalytic converters are fitted into automobiles for reducing emission of poisonous gases.

Catalytic converters use expensive metals namely Platinum-palladium and Rhodium as the catalysts. As the exhaust passes through the catalytic converter, they convert un-burnt hydrocarbons into carbon dioxide and water, and carbon monoxide to carbon dioxide and nitric oxide to nitrogen gas.

Compressed Natural Gas (CNG): It is made by compressing natural gas (natural gas mainly composed of CH₄). CNG is methane stored at high pressure.

• CNG burns most efficiently than petrol or diesel and it is hardly left un-burnt in automobiles
• CNG combustion produces fewer undesirable gases.
• CNG is cheaper than petrol or diesel, cannot be adulterated like petrol or diesel.

Norms are laid for fuels to control vehicular pollution. These norms help in reducing the sulphur and
aromatics content in petrol and diesel fuels.

According to Euro II norms: It limits Sulphur level at 350 parts-per-million (ppm) in diesel and 150 ppm in petrol. Aromatic hydrocarbons are to be contained at 42 % of the concerned fuel. These are European standards.

In India, equivalent to Euro norms are Bharat Stage Emission Standards, like Bharat Stage II (equivalent to Euro-II norms). Currently, in India, Bharat Stage IV emission norms are in use. Indian Government has announced to adopt Euro VI norms by 2020 by skipping Euro V norms altogether to control the increasing air pollution in India.

• Air Prevention and Control of Pollution Act came into force in 1981, but was amended in 1987 to include noise as an air pollutant.
• Noise: Undesired high level of sound. Noise is measured in decibel (dB).
• Noise generated by takeoff of a jet plane or rocket has intensity of 150 dB or more generated may damage ear drums thus permanently impairing hearing ability. Noise also causes sleeplessness, increased heart beating, altered breathing pattern, and stress in humans.
• Industrial noise is reduced by use of sound absorbent materials or by muffling noise.
• Horn-free zones are made around hospitals and schools. Laws are laid to limit the noise like sound-levels of crackers and of loudspeakers, timings after which loudspeakers cannot be played, etc.