POLLUTION
$\displaystyle \small \bullet$ Pollution is any undesirable change in physical, chemical or biological characteristics of air, land (soil), water. Agents that bring about such an undesirable change are called as pollutants.
$\displaystyle \small \bullet$ In order to control environmental pollution, the Government of India has passed the Environment (Protection) Act, 1986.

AIR POLLUTION AND ITS CONTROL
Effect of air pollution
$\displaystyle \small \bullet$ Cause injury to all living organisms.
$\displaystyle \small \bullet$ Reduce growth and yield of crops.
$\displaystyle \small \bullet$ Cause premature death of plants.
$\displaystyle \small \bullet$ Affects the respiratory system of human being.

$\displaystyle \small \bullet$ According to Central Pollution Control Board (CPCB), particulate size of less than 2.5 micrometers in diameter (PM 2.5) causes greatest harm to human health. These fine particulates can be inhaled deep into the lungs and can cause breathing and respiratory symptoms, irritation, inflammations and damage to the lungs and premature deaths.
$\displaystyle \small \bullet$ Pollution caused by thermal power plant: Thermal power plant and smelters release particulate matter and gaseous air pollutant.

Prevention of air pollution (To remove particulate matter)
Electrostatic precipitator (ESP)
$\displaystyle \small \bullet$ It is a device that removes suspended dust particles from a gas or exhaust by applying a high-voltage electrostatic charge and collecting the particles on charged plates.
$\displaystyle \small \bullet$ ESP can remove over 99% particulate matter present in the exhaust from a thermal power plant.
$\displaystyle \small \bullet$ It has electrode wires that are maintained at several thousand volts, which produce a corona that releases electrons.
$\displaystyle \small \bullet$ These electrons attach to dust particles giving them a net negative charge.
$\displaystyle \small \bullet$ The positively charged collecting plates are grounded and attract the negatively charged dust particles.
$\displaystyle \small \bullet$ The velocity of air between the plates must be low enough to allow the dust to fall.


Scrubber
$\displaystyle \small \bullet$ Scrubbers are one of the primary devices that control gaseous emissions, especially acid gases.
$\displaystyle \small \bullet$ Removes gases like sulphur dioxide.
$\displaystyle \small \bullet$ The exhaust is passed through a spray of water or lime.


Methods to reduce vehicular pollution
$\displaystyle \small \bullet$ Proper maintenance of automobiles along with use of lead-free petrol or diesel and use of catalytic converter.
Catalytic converter
$\displaystyle \small \bullet$ It is a vehicle emission control device that converts toxic pollutants in exhaust gas to less toxic pollutants by catalyzing a redox reaction.
$\displaystyle \small \bullet$ Have expensive metals namely platinum-palladium and rhodium as the catalysts.
$\displaystyle \small \bullet$ Catalysts are fitted into automobiles for reducing emission of poisonous gases.
$\displaystyle \small \bullet$ The unburnt hydrocarbons are converted into carbon dioxide and water, and carbon monoxide and nitric oxide are changed to carbon dioxide and nitrogen gas, respectively.
$\displaystyle \small \bullet$ Motor vehicles equipped with catalytic converter should use unleaded petrol because lead in the petrol inactivates the catalyst.

Controlling Vehicular Pollution: A case study of Delhi
$\displaystyle \small \bullet$ Delhi leads the country in high levels of air-pollution, with its very large population of vehicular traffic – it has more cars than the states of Gujarat and West Bengal put together.
$\displaystyle \small \bullet$ In the 1990s, Delhi ranked fourth among the 41 most polluted cities of the world.
$\displaystyle \small \bullet$ After being censured by the Supreme Court, the government was asked to take appropriate measures, including switching over the entire fleet of public transport, i.e., buses, from diesel to compressed natural gas (CNG).
$\displaystyle \small \bullet$ All the buses of Delhi were converted to run on CNG by the end of 2002.

Advantage of CNG
$\displaystyle \small \bullet$ CNG burns most efficiently.
$\displaystyle \small \bullet$ Very little remain unburnt.
$\displaystyle \small \bullet$ Cannot be siphoned.
$\displaystyle \small \bullet$ CNG is cheaper than petrol or diesel, cannot be adulterated like petrol or diesel.

Problem of Use of CNG
$\displaystyle \small \bullet$ Difficulty  is  laying  down  pipelines  to  deliver  CNG  through  distribution points/pumps.
$\displaystyle \small \bullet$ Non-assurance of uninterrupted supply.

Other parallel steps taken in Delhi
$\displaystyle \small \bullet$ Phasing out of old vehicles.
$\displaystyle \small \bullet$ Use of unleaded petrol.
$\displaystyle \small \bullet$ Use of low-sulphur petrol and diesel.
$\displaystyle \small \bullet$ Use of catalytic converters in vehicles.
$\displaystyle \small \bullet$ Application of stringent pollution level norms for vehicles.

$\displaystyle \small \bullet$ The Government of India through a new auto fuel policy has laid out a roadmap to cut down vehicular pollution in Indian cities.
$\displaystyle \small \bullet$ Steadily reducing the sulphur and aromatics content in petrol and diesel fuels.
$\displaystyle \small \bullet$ Euro II norms, for example, stipulates that sulphur be controlled at 350 parts-per-million (ppm) in diesel and 150 ppm in petrol.
$\displaystyle \small \bullet$ Aromatic hydrocarbons are to be contained at 42% of the concerned fuel.
$\displaystyle \small \bullet$ According to the roadmap, is to reduce sulphur to 50 ppm in petrol and diesel and bring down the aromatic hydrocarbons level to 35%.


NOISE POLLUTION
$\displaystyle \small \bullet$ In India, the Air (Prevention and Control of Pollution) Act came into force in 1981, but was amended in 1987 to include noise as an air pollutant.
$\displaystyle \small \bullet$ Noise is undesired high level of sound.
Harmful Effect of Noise Pollution
$\displaystyle \small \bullet$ Psychological and physiological disorders in humans.
$\displaystyle \small \bullet$ High sound level, 150 dB or more generated by take off of a jet plane or rocket, may damage ear drums thus permanently impairing hearing ability.
$\displaystyle \small \bullet$ Noise also causes sleeplessness, increased heart beating, altered breathing pattern.
Prevention of Noise Pollution
$\displaystyle \small \bullet$ Reduction of noise in industries can be affected by use of sound absorbent materials or by muffling noise.
$\displaystyle \small \bullet$ Stringent following of laws laid down in relation to noise like delimitation of horn-free zones around hospitals and schools.
$\displaystyle \small \bullet$ Permissible sound-levels of crackers and of loudspeakers.
$\displaystyle \small \bullet$ Timings after which loudspeakers cannot be played.