Air Pollution  Air pollution is any undesirable change in physical, chemical or biological characteristics of air.  Agents that bring about such an undesirable change are called as pollutants.  These pollutants may be particulate matter (like-dust particles, pollen,etc) or gaseous pollutants.

Harmful effects of air pollutants  Air pollutants cause injury to all living organisms.  They reduce growth and yield of crops and cause premature death of plants of plants.  Air pollutants also deleteriously affect the respiratory system of humans and animals.  These harmful effects depend on the:- 1.concentration of pollutants, 2.duration of exposure 3.and the organism

Ways of Removing Particulate Matter There are many ways of removing particulate matter:-  ELECROSTATIC PRECIPITATOR  Can remove 99% part. matter present in the exhaust from a thermal power plant.  It has electrode wires that are maintained at several thousand volts, which produce a corona that releases electrons.  These electrons attach to the dust particles giving them a net –ve charge.

 The collecting plates are grounded and attract the charged dust particles.

 SCRUBBER  A scrubber can remove gases like sulphur dioxide.  In a scrubber, the exhaust is passed through a spray of water or lime. Note:-  Recently we have realised the dangers of particulate matter that are very very small and are not removed by these precipitators.  According to Central Pollution Control Board (CPCB), particulate size 2.5 micrometers or less in diameter are responsible for causing the greatest harm to human health.

Mechanism of catalytic converter Catalytic converters have expensive metals namely platinum, palladium and rhodium as catalyst. As the exhaust passes through the catalytic converter, unburned hydrocarbons are converted into carbon dioxide and water,and carbon monoxide and nitric acid are changed to carbon dioxide and nitrogen gas. Motor vehicles with catalytic converter should use unleaded petrol because lead in the petrol inactivates the catalyst.

 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.  Noise is undesired high level of sound.  Noise causes psychological and physiological disorders in humans.  A brief exposure to extremely high sound level, 150db or more may damage ear drums thus permanently impairing hearing ability.  Even chronic exposure to a relatively lower noise level of cities may permanently damage hearing abilities of humans.

 Noise also causes sleeplessness, increased heart beat, altered breathing pattern, thus considerably stressing humans.  Unnecessary sources of noise pollution around us should be reduced immediately.  Noise in our industries can be reduced by the use of sound absorbing materials or by muffling noise.  Stringent laws in relation to noise pollution should be enforced strictly.

Controlling Vehicular Air Pollution: A Case Study of Delhi  Delhi leads the country in level of air pollution-it has more cars than the states of Gujarat and west Bengal put together.  In the 90s, Delhi ranked 4 th among the 41 most polluted cities of the world.  A public interest litigation (PIL) was filed in Supreme Court of India in relation to the air pollution in Delhi.  Under its directives, the Govt. was asked to take appropriate measures within a

 specified time.  By the end of year 2002, entire fleet of public transport i.e., the buses were switched over to Compressed Natural Gas (CNG) in Delhi. Why is CNG better than diesel or petrol?  CNG burns more efficiently and very little of it is left unburned.  CNG is cheaper than petrol or diesel.  It cannot be siphoned off by thieves or adulterated like petrol or diesel