NCERT Revision Notes Chapter 18 Pollution of Air and Water Class 8 Science

Answer

• Introduction

• Air pollution

→ Sources of air pollution

• Types of air pollutants

→ Prevention of air pollution

• Acid Rain

• Water Pollution

→ Sources of water pollution in Ganga River

• Types of water pollutants

→ Industrial Waste

→ Agricultural Waste

→ Release of Superheated water

• Methods of preventing water pollution

• Conservation of Water

→ Rainwater harvesting

• Portable Water

→ Methods of obtaining portable water

• Greenhouse effect

→ Causes of Greenhouse effect

→ Green house gases

• Global warming

Answer

→ The layer of air present around the earth is called atmosphere.

→ Atmosphere is composed of 78% of nitrogen, 21% of oxygen, and 1% percent other gases such as carbon dioxide, ozone, water vapour, methane, etc.

Answer

→ The phenomenon of contamination of air with unwanted substances so that it becomes harmful for living organisms and non-living substances is known as air pollution.

→ The substances, which cause air pollution, are called air pollutants.

Sources of air pollution

(i) Power plants

(ii) Factories

(iii) Automobiles

(iv) Burning of firewood

Answer

(i) Carbon monoxide

→ It is a colourless poisonous gas.

→ It is produced from incomplete burning of fossil fuels.

(ii) Smog

→ It is made up of smoke and fog.

(iii) Sulphur dioxide

→ It is produced from combustion of fuels.

(iv) Nitrogen dioxide

→ It is produced from incomplete burning of fuels.

(v) Chlorofluorocarbons (CFCs)

→ They are released from refrigerators, air conditioners, and aerosol sprays.

→ They cause damage to the ozone layer resulting in the formation of ozone hole.

(vi) Suspended particulate matter

→ It comprises of tiny particles, which remain suspended in air for a long time.

→ They are produced during burning of fossil fuels in power plants, mining, steel making, and other industrial processes.

→ They reduce visibility and cause haze.

→ They cause respiratory diseases on inhalation.

→ Soot released from Mathura refinery has caused yellowing of the marble of Taj Mahal.

Prevention of air pollution

→ Use of clear fuels such as CNG, LPG, and unleaded petrol in public and private transport.

→ Use of renewable sources of energy such as solar, wind, and hydel energy.

→ Planting more and more trees to prevent pollution.

→ Prevent burning of dry leaves and use them in composting.

→ Kyoto protocol is an agreement between various countries for reducing green house emission.

Answer

→ It is formed when sulphur dioxide and nitrogen dioxide present in air react with water droplets to form nitric and sulphuric acid.

→ When it rains, it brings these acids along with it, which causes damage to plants, animals, and monuments.

→ Acid rain has caused corrosion of the marble of Taj Mahal

Answer

→ The addition of harmful substances to water, as a result of which its physical, chemical, and

biological properties get altered, is called water pollution.

→ Substances that pollute water are called water pollutants.

Sources of water pollution in Ganga river

→ Untreated discharges from textile, paper and sugar mills, and oil refineries.

→ Disposal of agricultural discharge from near-by fields, which are rich in pesticides and weedicides, into the river.

→ Flow of untreated domestic sewage into the river.

→ Cremation of dead bodies into the river.

→ Immersion of idols of gods and goddesses, flowers, garbage, and polythene bags into the river.

→ Ganga Action Plan aimed to reduce the pollution levels in the river.

Answer

→ Domestic sewage

→ It is composed of food wastes, detergents, and disease-causing pathogens.

→ The bacteria present in faecal matter of mammals indicate the pollution levels in a river and if such water is consumed, it may cause various diseases.

Industrial waste

→ It is rich in toxic chemicals such as arsenic, fluorides, and lead.

→ It causes toxicity in plants and animals.

→ It affects the soil by causing changes in acidity and growth of worms.

Agricultural waste

→ It is rich in agricultural pesticides and weedicides.

→ It causes ground water pollution.

→ It causes an increase in the population of algae in water.

→ When these algae die, they are acted upon by decomposers, which use lots of oxygen dissolved in water for this purpose.

→ This results in the death of fishes and other aquatic organisms.

Release of Superheated Water

→ The release of superheated water from some industries and nuclear power plants causes thermal pollution of the water bodies.

→ The abrupt change in the temperature of water body can kill the fish and other organisms adapted to particular temperature range.

Answer

→ Industrial waste must be chemically treated to remove harmful substances before dumping into the water bodies.

→ Disposal of human and animal excreta into water should be avoided.

→ Sewage water must be treated before releasing into the rivers.

Answer

→ Reusing the waste water from the kitchen (water that has been used to wash vegetables, etc.) to water the plants in the garden.

→ Turning the tap off while brushing or shaving.

→ Checking for leaky taps and fixing them up.

Rainwater harvesting

→ Using improved farming and irrigation techniques

→ Preventing pollution of water

→ Conserving and replenishing ground water

→ Proper removal of silt from water bodies

→ Preventing cutting of trees

→ Prevention of water pollution

→ Proper treatment of industrial waste and domestic waste before their disposal into rivers.

→ Strict implementation of environmental laws in industrial units.

→ Reusing water used in kitchens (such as to wash vegetables) for watering plants.

→ Getting the leaky taps checked and preventing wastage of water.

Answer

→ Water that is fit for drinking is called potable water.

Methods of obtaining potable water

(i) Physical methods

→ Boiling of water

→ Use of domestic filters such as candle type filter

(ii) Chemical method

→ Use of chlorine tablets

Answer

→ Trapping of heat by gases (CO2 ) in the atmosphere.

→ Gases that cause the greenhouse effect are responsible for increasing the temperature of the Earth and thus contributing to the phenomenon called global warming.

Causes of Green house effect

→ A part of solar radiations cause warming of the earth’s surface.

→ A part of solar radiation is reflected back, which is trapped by the earth’s atmosphere.

→ This phenomenon is called green house effect.

Green house gases

→ These are the gases, which trap the solar radiations, and in this way, are responsible for the increase in the temperature of Earth.

→ The examples include carbon dioxide, methane, nitrous oxide, and water vapours.

Answer

→ The CO2 level in atmosphere is increasing due to various human activities such as deforestation and burning of fossil fuels.

→ Build up of CO2 in the atmosphere will result in a rise in the average temperature of earth’s atmosphere, leading to global warming.

→ Global warming will lead to melting of glaciers and increase in the sea level.