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(c) Catalytic convertors are fitted into automobiles for
reducing emission of poisonous gases like NO 2 and CO.
• They are made of expensive metals like platinum, palladium and rhodium as catalysts.
• When exhaust passes through the catalytic convertor, nitric oxide splits into nitrogen and
oxygen; carbon monoxide is oxidised into carbon dioxide and unburnt hydrocarbons get
burnt completely into CO 2 and H 2O.
• Unleaded petrol should be used in motor vehicles fitted with catalytic convertor as leaded
petrol inactivates the catalyst.
(i) A Case Study— Control of Air Pollution in Delhi
(a) Delhi leads the country in high levels of air pollution due to large numbers of vehicles. In
1990s, Delhi ranked fourth among the 41 most polluted cities of the world.
(b) As per directives of Supreme Court, all buses of Delhi were converted to run on
Compressed Natural Gas (CNG) by the end of 2002.
(c) Benefits of CNG over diesel/petrol
* Burns most efficiently and leaves no unburnt remains.
– Cheaper than diesel/petrol.
* Cannot be siphoned off by thieves and adulterated like petrol or diesel.
(d) Other ways to reduce vehicular pollution
* Phasing out of old vehicles.
* Use of unleaded petrol.
* Use of low-sulphur petrol and diesel.
* Application of stringent pollution-level norms for vehicles.
* Use of catalytic convertors in vehicles.
(vi) Auto Fuel Policy of Government of India
(a) Euro II norms stipulate that sulphur be controlled 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.
(b) According to it, all automobiles have to meet the Euro III emission specification in eleven
Indian cities by 1 April, 2005.
(c) The same eleven cities have to meet the Euro IV norms by 1 April, 2010.
(d) The rest of the country will have Euro III emission norm compliant automobiles and fuels
by 2010.
(e) By all these efforts, a substantial fall in CO 2 and SO 2 level has been found in Delhi
between 1997 and 2005.
3. Noise pollution is undesirable high level of sound. In India, the Air (Prevention and Control
of Pollution) Act came into force in 1881, but was amended in 1987 to includes noise as art
air pollutant.
Noise measurement Sound is expressed in decibels (dB). A sound of over 115 dB is very
harmful for ears. Prolonged exposure to noise level above 80 dB leads to perma nent hearing
loss.
(i) Causes are
(a) Use of loudspeakers and music systems. (b) Jet planes and rockets take-off.
(c) Industrial, factory noises, etc.
(ii) Harmful effects are sleeplessness, stress, increased heartbeat, breathing problems,
damage to ear drums and impaired hearing ability.
(iii) Control Methods