Science Class Eight  

Air and Water Pollution


When the level of contaminants in air becomes so much that air becomes harmful for living beings; it is called air pollution.

Causes of Air Pollution: The main causes of air pollution are as follows:

(a) Exhaust from Automobiles: Most of the automobiles use fossil fuels. Burning of fossil fuel releases carbon dioxide and carbon monoxide. Carbon dioxide is a greenhouse gas. Carbon monoxide is a poisonous gas even at low concentrations.

(b) Exhaust from Factories and Power Plants: Coal is the main fuel being used in factories. Burning of coal produces carbon dioxide and oxides of sulphur. Oxides of sulphur and nitrogen form acid rain when they mix with rainwater. Acid rain is harmful for living beings and also for buildings and monuments.

(c) Chlorofluorocarbons (CFCs): These are compounds of carbon and halogens and are used as refrigerant. These are also used in pressurized cans. Excess level of CFCs in the atmosphere damages the ozone layer. Ozone layer works like a shield and prevents the harmful ultraviolet radiations from reaching up to the living beings. Any damage in the ozone layer can be very harmful.

(d) Suspended Particulate Matters (SPMs): Some fine particles remain suspended in the air. These are called suspended particulate matters. Stone quarries and various other factories contribute to SPMs.

Effects of Air Pollution:

Greenhouse Effect: Greenhouse gases trap solar radiation which increases the overall temperature of the atmosphere. Carbon dioxide and methane are examples of greenhouse gases. The greenhouse effect leads to global warming. Global warming has resulted in melting of the glacial ice. Scientists have predicted that many coastal cities would be completely submerged in the near future because of glacial melting. Global warming has also caused drastic changes in weather. Increased instances of flash floods and erratic weather are being attributed to global warming.

Smog: A mixture of fog and smoke is called smog. Smog creates a blanket of haze in the sky. This reduces visibility which can give trouble to pilots and drivers.

Respiratory Diseases: Cases of respiratory diseases; like asthma are on the rise because of increased levels of air pollution.

Acid Rain: Acid rain happens because of the presence of oxides of nitrogen and sulphur in the atmosphere. Acid rain can be very harmful for living beings. Moreover, acid rain can also damage buildings and monuments. The case of Taj Mahal is a reminder of the horrible effects of acid rain. The Taj Mahal was built by using white marbles. But now-a-days, it does not look white rather looks a pale white. Acid rain is corroding the marble of the Taj Mahal. An order by the Supreme Court of India directed all the factories to shift from the vicinity of Taj Mahal. After that order, only battery operated vehicles are allowed to be driven near this monument.

Deforestation: Deforestation is a major cause of air pollution. Reduced forest cover means there are less number of trees to convert carbon dioxide into oxygen. This has led to increased levels of carbon dioxide in the atmosphere.

How to Prevent Air Pollution?

Some of the ways to prevent air pollution are as follows:

  • Switching to cleaner fuels; like CNG. The Delhi government fitted CNG kit in all the DTC (Delhi Transport Corporation) buses; after a court order. All the public transport vehicles in Delhi now use CNG. This has helped a lot in improving the air quality of Delhi. Many private vehicles also now use CNG.
  • Increasing the use of public transport can also help in reducing air pollution. This will help in reducing the number of cars on the road.
  • Walking and cycling are very good for health as well as for the environment. You can walk or use a bicycle for a short distance commute. Instead of using a bus or a car; you should use a bicycle for going to school.
  • Electrostatic precipitators should be fitted in chimneys of factories. This helps in reducing the amount of SPMs in the air. Similarly, catalytic converters are fitted in the exhaust system of vehicles. This helps in reducing the poisonous substances in vehicle exhaust.
  • More trees should be planted. We know that trees convert carbon dioxide into oxygen; during photosynthesis. Thus, trees help in maintaining the balance of carbon dioxide and oxygen.

When the level of contaminants in water reaches to such a level that water becomes harmful for living beings, it is called water pollution.

Causes of Water Pollution: Some of the causes of water pollution are as follows:

Untreated Sewage: In India, this is a common practice to discharge untreated sewage and effluents into the nearest water body. Most of the rivers and ponds in India are highly polluted because of this.

Age Old Practices: Many people in India use a pond or a river for bathing, for defecating and for washing clothes. Dead bodies are preferably cremated near a river bank. Sometimes, half burnt carcass is also disposed off in the rivers.

Use of Fertilisers and Insecticides: Increased use of fertilisers and insecticides also results in pollution of groundwater.

Case of Kanpur: Kanpur is an important industrial town in Uttar Pradesh. There are numerous tanneries in this city. Additionally, there are many other factories which manufacture different items. Although rules are in place but most of the factory owners seldom obey these rules. Untreated effluents are being discharged in the Ganges. The Ganges looks like a filthy drain when it flows through Kanpur. The quality of water is so bad that fishes die in huge numbers. Cases of skin diseases are on the rise in this city; because of very high level of water pollution.

Effects of Water Pollution: Water pollution can result in contamination of groundwater. Farm output is reduced because of polluted water. Fishermen are unable to carry on their traditional occupation because of low fish output. Water borne diseases; like cholera and jaundice; are on the rise because of water pollution.

How to Prevent Water Pollution?

Water pollution can be prevented by following ways and means.

  • Installing sewage treatment plants at strategic locations can help. It should be ensured that untreated sewage is never discharged into a water body. The law enforcement agencies should be strict so that factories should install effluent treatment plants.
  • The Ganga Action Plan was launched in 1985 to clean up the Ganges. Billions of rupees have been poured in this Action Plan but results are nowhere to be seen. At most of the places; this holy river is highly polluted. But we need to take some drastic measures to save this river from imminent disaster.
Potable Water

Water which is fit for drinking is called potable water. We have seen that water at most of the places is highly polluted. Hence, all of us need to apply some methods of water purification. Water purification is necessary as it helps in preventing water borne diseases. By doing so; many deaths can be easily prevented. Some of the methods of water purification are as follows:

  1. Boiling: This is the simplest method of water purification. Boiling kills most of the germs in water.
  2. Chlorine Tablet: Chlorine tablet is added to water and this helps in killing the germs. Chlorine tablets are ideal for rural areas and for those families who cannot afford costly water filters.
  3. Water Filters: Different types of water filters are available in the market. The cheapest water filters have ceramic candles through which water is filtered. Some of the water filters have filters made of charcoal. Some costly water filters work on Reverse Osmosis and hence they are called RO filters. You will read about reverse osmosis in your higher classes.

Air and Water Pollution - ncert solution

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