Chapter 18 Pollution of Air and Water notes class 8th science

Introduction

→ 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.

Air pollution

→ 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

Types of air pollutants

(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.

Acid rain

→ 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

Water pollution

→ 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.

Types of water pollutants

→ 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.

Methods of preventing water pollution

→ 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.

Conservation of water

→ 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.

Potable water

→ 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

Greenhouse effect

→ 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.

Global warming

→ 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.