Environmental Issues - Notes | Class 12 | Part 1: Air Pollution and its Control


Pollution is any undesirable change in physical, chemical or biological characteristics of air, land, water or soil. Human population explosion increases the demand for food, water, home, electricity, automobiles etc. It leads to pollution.

The Government of India has passed the Environment (Protection) Act, 1986 to control environmental pollution and protect and improve the quality of our environment.


Causes of air pollution:
  • Particulate & gaseous air pollutants from smokestacks of thermal power plants, smelters etc.
According to Central Pollution Control Board (CPCB), particulate size of less than 2.5mm in diameter (PM 2.5) causes greatest harm to human health.
  • Pollutants from automobiles.
Harmful effects of air pollution:
  • Particulates cause respiratory problems, irritation, inflammations & damage to lungs and premature deaths.
  • Reduction in growth and yield of crops and premature death of plants.
Control of air pollution:
  • Separate/filter out particulate matters before releasing the harmless gases into the atmosphere.
  • Use of lead-free petrol or diesel.
  • Use of catalytic converters.
  • Phasing out of old vehicles.
  • Use of low-sulphur petrol and diesel.
  • Application of pollution-level norms for vehicles, etc.
  • Use of compressed natural gas (CNG). It is used in Delhi, in public transport (buses).
Advantages of CNG:
  • It is better and cheaper than petrol & diesel. It burns almost completely.
  • It cannot be siphoned off by thieves and adulterated.
Main problem of CNG: 

Difficulty of laying down pipelines to deliver CNG through distribution points/pumps.

Catalytic converter: 

It is the device to reduce emission of poisonous gases. It has platinum-palladium & rhodium as catalysts. This converts

Unburnt hydrocarbons → CO2 + water

Carbon monoxide → CO2

Nitric oxide → Nitrogen

Motor vehicles having catalytic converter should use unleaded petrol because lead in petrol inactivates the catalyst.

Electrostatic precipitator 

It is the device to remove particulate matter.

It can remove over 99% particulate matter present in the exhaust from a thermal power plant.

The electrons released from electrode wires (at several thousand volts) attach to dust particles giving a negative charge. The collecting plates attract charged dust particles.

The velocity of air between the plates must be low enough to allow the dust to fall.

A scrubber removes gases like SO2. In this, the exhaust is passed through a spray of water or lime.

Very small particulates are not removed by this precipitator.


Noise is undesired high level of sound.

In India, the Air (Prevention & Control of Pollution) Act (1981) was amended in 1987 to include noise as an air pollutant.

Sources of noise pollution:

Music instruments, loudspeaker, crackers, industries etc.

Harmful effects of noise:
  • Noise causes psychological and physiological disorders.
  • The sound level above 150 dB (generated by takeoff of a jet plane or rocket) may damage ear drums.
  • Chronic exposure to relatively lower noise may damage hearing abilities of humans.
  • Sleeplessness, increased heartbeat & breathing, stress etc.
Control of noise pollution:
  • Use of sound absorbent materials in industries.
  • Delimitation of horn-free zones around hospitals & schools.
  • Permissible sound-levels of crackers and loudspeakers.
  • Delimit the timings of using loudspeakers.
Laws & policies in India to control vehicular pollution 
  • Auto fuel policy: To cut down vehicular pollution in Indian cities.
  • Euro III norms:
Control sulphur content at 350 ppm (parts per million) in diesel and 150 ppm in petrol.
Level of aromatic hydrocarbons is to be at 42% of the fuel.
In future: Reduce sulphur to 50 ppm in petrol & diesel and bring down the level to 35%.
Upgrade vehicle engines.
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