Class 8 SCIENCE Chapter 18 Air and water pollution notes and NCERT QUESTIONS AND ANSWERS, NOTES

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Air And Water Pollution

NCERT QUESTION ANSWERS AND LESSON SUMMARY NOTES

Question 1:

What are the different ways in which water gets contaminated?

Answer :

Water gets contaminated by the addition of:
(i) Agricultural chemicals: Farmers use excessive amounts of pesticides and fertilizers to increase crop production. These chemicals get carried away to the water bodies due to rains and floods which lead to water pollution.
(ii) Industrial wastes: Industries release harmful chemical wastes into water sources, thereby polluting them.
(iii) Sewage wastes: Waste materials from kitchens, toilets, and laundry sources are also responsible for contaminating water.

 

Question 2:

At an individual level, how can you help reduce air pollution?

Answer :

An individual can reduce air pollution by:
(i) Avoiding the use of cars as much as possible and by using public transport whenever possible.
(ii) By not using vehicles for short distances.
(iii) By using clean fuels such as LPG and CNG instead of diesel and petrol.
(iv) Always disposing the garbage properly and not burning it.
(v) Controlling the emissions from vehicles and household chimneys.

Question 3:

Clear, transparent water is always fit for drinking. Comment.

Answer :

No. Clear and transparent water is not always fit for drinking. Water might appear clean, but it may contain some disease causing micro-organisms and other dissolved impurities. Hence, it is advised to purify water before drinking. Purification can be done by water purifying systems or by boiling the water.

Question 4:

You are a member of the municipal body of your town.
Make a list of measures that would help your town to ensure the supply of clean water to all its residents.

Answer :

To ensure the supply of clean water to all residents the following steps must be taken:
(i) The main water source must be built in clean surroundings and should be maintained properly.
(ii) Chemical methods such as chlorination must be used for purifying water.
(iii) The area around water pipes must also be clean.

Question 5:

Explain the differences between pure air and polluted air.

Answer :

Pure air contains around 78% nitrogen, 21% oxygen, and 0.03% carbon dioxide. Other gases such as argon, methane, ozone, and water vapours are also present in small quantities. When this composition of air is altered by the addition of harmful substances or gases such as nitrogen dioxide, sulphur dioxide, carbon monoxide, and particulate matter, then the air is said to be polluted.

Question 6:

Explain circumstances leading to acid rain. How does acid rain affect us?

Answer :

Burning of fossil fuels such as coal and diesel releases a variety of pollutants such as sulphur dioxide and nitrogen dioxide into the atmosphere. These pollutants react with water vapours present in the atmosphere to form sulphuric acid and nitric acid respectively. These acids come down with the rain, thereby resulting in acid rain.
Effects of acid rain:
(i) Acid rains damage crops.
(ii) Acid rains corrode buildings and structures especially those made of marble such as Taj Mahal.

Question 7:

Which of the following is not a greenhouse gas?
(a) Carbon dioxide
(b) Sulphur dioxide
(c) Methane
(d) Nitrogen

Answer :

(d) Nitrogen

Question 8:

Describe the ‘Greenhouse Effect’ in your own words.

Answer :

Greenhouse effect may lead to global warming, i.e., an overall increase in the average temperature of the Earth. Greenhouse effect is caused by greenhouse gases. Examples of greenhouse gases include carbon dioxide, methane, and water vapour. When solar radiations reach the Earth, some of these radiations are absorbed by earth and then released back to the atmosphere. Greenhouse gases present in the atmosphere trap these radiations and do not allow heat to leave. This helps in keeping our planet warm and thus, helps in human survival. However, an indiscriminate increase in the amount of greenhouse gases can lead to excessive increase in the Earth’s temperature leading to global warming.

 

Question 9:

Prepare a brief speech on global warming. You have to deliver the speech in your class.

Answer :

Global warming is an increase in the average temperature of the Earth’s surface. It occurs as a result of an increased concentration of greenhouse gases in the atmosphere. The greenhouse gases include carbon dioxide, methane, and water vapour. These gases trap solar radiations released back by the Earth. This helps in keeping our planet warm and thus, helps in human survival. However, an increase in the amount of greenhouse gases can lead to an increase in the Earth’s temperature leading to global warming.

Question 10:

Describe the threat to the beauty of the Taj Mahal.

Answer :

Acid rain is a major threat to the beauty of the Taj Mahal. When acid rains fall on the monument (that is completely made of marble), they react with marble to form a powder-like substance that is then washed away by the rain. This phenomenon is known as marble cancer. Also, the soot particles emitted from the Mathura oil refinery located near Agra is leading to the yellowing of the marble.

Question 11:

Why does the increased level of nutrients in the water affect the survival of aquatic organisms?

Answer :

An increase in the level of nutrients in a water body leads to an excessive increase in the population of algae in the water body. When these algae die, they serve as food for decomposers. A lot of oxygen is utilised in this process, consequently leading to a decrease in the level of oxygen dissolved in the water body. This in turn causes fishes and other aquatic organisms to die.

 

Substances that cause harmful changes in the air are called pollutants. Air pollution is caused due to the presence of pollutants in the air.
Air pollution is caused by burning fossil fuels, like coal and petroleum, in industries, power plants and vehicles, and by burning of firewood and dung cakes. Pollutants are also released into the air by natural events like a dust storm, forest fire or volcanic eruption.
Incomplete burning of fossil fuels, like petrol and diesel, results in the production of colourless, odourless and toxic carbon monoxide gas.
Smog is a mix, in the air, of smoke and chemicals with fog.
The chemical components of smog can include ozone, sulphur dioxide, nitrogen dioxide and carbon monoxide.
Smog can trigger breathing difficulties like asthma and coughing.
Pollutants like sulphur dioxide and nitrogen dioxide are released in large quantities by petroleum refineries.
These emissions can cause respiratory problems and also permanent lung damage.
CFCs or chlorofluorocarbons are synthetic products that contain carbon, chlorine and fluorine. They were formerly used as a refrigerant and as a propellant in aerosol or air sprays.

CFCs contribute to the depletion of the ozone layer that protects us from the harmful ultraviolet rays of the sun.
Soot is released when automobiles burn fossil fuels, like petrol and diesel.
Pollutants like sulphur dioxide and nitrogen dioxide, which are produced by industries like rubber processing, automobile chemicals and the Mathura oil refinery near Agra, are responsible for the decolourisation of the Taj Mahal.
These gases react with water vapour in the atmosphere and form sulphuric acid and nitric acid. Precipitation carries these acids back to the earth as acid rain.
The corrosion of the Taj Mahal due to acid rain is called ‘marble cancer.’
Global warming has already started melting the polar ice caps, which has resulted in a rise in the global sea level.
Gases, like methane, nitrous oxide and water vapour, also contribute to the greenhouse effect, and, along with carbon dioxide, are collectively called the greenhouse gases.
Steps to prevent air pollution:
Use of fuels like CNG and unleaded petrol in automobiles.
Switching to alternative fuels, like solar energy, hydropower and wind energy.
Planting trees.
Travelling to school on a bicycle or on public transport or car pooling.
Avoiding the burning of leaves, trash and vegetable matter.
Restricting cigarette smoking.
Water covers two-thirds of the earth’s surface and makes up 75 per cent of the human body.
A water body is said to be polluted when toxic substances damage it, making it undrinkable and also dangerous for organisms to live in it.
Harmful substances, like sewage, silt, toxic chemicals and domestic waste, are called water pollutants. They spoil the quality of water by altering its smell and colour, and render it unfit for drinking.
Pollution can enter a body of water in many ways, such as domestic sewage, agricultural run-off containing fertilisers and pesticides, eroded soil, acid rain, chemicals released from industries or other wastes from cities and towns.
At places along the Ganga, people bathe, wash clothes and even defecate in the water. They also throw huge quantities of garbage, flowers, idols of gods and goddesses, untreated sewage, animal carcases and non-biodegradable polythene bags directly into the river.
Chemical contamination of water due to chemicals, such as compounds of arsenic, fluorides and lead, cause plants and animals to die. The soil is also affected by polluted water, causing changes in its acidity, and, therefore, the growth of plant life.
Polluted water is unsuitable for drinking, recreation, agriculture and industry.

Contaminated water destroys aquatic life and reduces its reproductive ability.
Water pollution drastically reduces the quantity of dissolved oxygen in water, which results in the death of aquatic organisms. Anaerobic micro-organisms release gases like methane and hydrogen sulphide, leaving a foul-smelling, waste-filled body of water.
The large quantities of chemicals that are washed in from the fields are responsible for the excessive growth of algae. Once the algae die, it serves as a food for bacteria. As a result, a lot of oxygen in the water is used up and many aquatic organisms die.
Water that is suitable for drinking is called potable water. Sewage treatment plants treat wastewater to purify it before releasing it back into rivers and lakes. Municipal bodies treat water before supplying it to our households.
Some popular ways of making water potable are:

• Using candle type water filters
• Boiling
• Chlorination

Reduce, reuse and recycle is a popular mantra and one that is so important for us to practise.
Steps to conserve water:
Rain water harvesting
Using drip irrigation method in agriculture
Reusing the water used to wash vegetables
Minimising water consumption

 

Definition: Pollution is the introduction of contaminants into an environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances, or energy, such as noise, heat, or light energy. Pollutants, the elements of pollution, can be foreign substances or energies, or naturally occurring; when naturally occurring, they are considered contaminants when they exceed natural levels. Pollution is often classed as point source or non point source pollution.

Air Pollution

Air pollution is the introduction of chemicals, particulate matter, or biological materials that cause harm or discomfort to humans or other living organisms, or damages the natural environment, into the atmosphere.

The atmosphere is a complex, dynamic natural gaseous system that is essential to support life on planet Earth. Stratospheric ozone depletion due to air pollution has long been recognized as a threat to human health as well as to the Earth's ecosystems.

Causes of Air Pollution:

The substances which contaminate the air are called air pollutants. Sometimes, such substances may come from natural sources like smoke and dust arising from forest fires or volcanic eruptions. Pollutants are also added to the atmosphere by human activities. The sources of air pollutants are factories, power plants, automobile exhausts and burning of firewood and dung cakes.

Vehicles produce high levels of pollutants like carbon monoxide, carbon dioxide, nitrogen oxides and smoke. Carbon monoxide is produced from incomplete burning of fuels such as petrol and diesel. It is a poisonous gas. It reduces the oxygen-carrying capacity of the blood. There is thick fog-like layer in the atmosphere, especially during winters. This is smog which is made up of smoke and fog. Smoke may contain oxides of nitrogen which combine with other air pollutants and fog to form smog. The smog causes breathing difficulties such as asthma, cough and wheezing in children. Many industries are also responsible for causing air pollution. Petroleum refineries are a major source of gaseous pollutants like sulphur dioxide and nitrogen dioxide. Sulphur dioxide is produced by combustion of fuels like coal in power plants. It can cause respiratory problems, including permanent lung damage.

Other kinds of pollutants are chlorofluorocarbons (CFCs) which are used in refrigerators, air conditioners and aerosol sprays. CFCs damage the ozone layer of the atmosphere.

In addition to the above mentioned gases, automobiles which burn diesel and petrol also produce tiny particles which remain suspended in air for long periods. They reduce visibility. When inhaled, they cause diseases. Such particles are also produced during industrial processes like steel making and mining. Power plants give out tiny ash particles which also pollute the atmosphere.

Case Study: - The Taj Mahal

Over the past 2 decades, India’s most famous tourist attraction, Taj Mahal located in Agra, has become a matter of concern. Experts have warned that pollutants in air are discolouring its white marble. So, it is not only living organisms that get affected by polluted air but non-living things like buildings, monuments and statues also get affected. The industries located in and around Agra like rubber processing, automobile, chemicals and especially the Mathura oil refinery, have been responsible for producing pollutants like sulphur dioxide and nitrogen dioxide. These gases react with the water vapour present in the atmosphere to form sulphuric acid and nitric acid. The acids drop down with rain, making the rain acidic. This is called acid rain. Acid rain corrodes the marble of the monument. The phenomenon is also called “Marble cancer”. Suspended particulate matter, such as the soot particles emitted by Mathura oil refinery, has contributed towards yellowing of the marble.

Greenhouse Effect

We know that the sun’s rays warm the earth’s surface. A part of the radiation that falls on the earth is absorbed by it and a part is reflected back into space. A part of the reflected radiation is trapped by the atmosphere. The trapped radiations further warm the earth. The trapped heat warms the green house. The trapping of radiations by the earth’s atmosphere is similar. That is why it is called the greenhouse effect. Without this process, life would not have been possible on the earth. But now it threatens life. CO2 is one of the gases responsible for this effect.

Global Warming

CO₂ is continuously being released because of human activities. On the other hand, area under forests is decreasing. Plants utilize CO₂ from the atmosphere for photosynthesis, thereby decreasing the amount of CO₂ in the air. Deforestation leads to an increase in the amount of CO₂ in the air because the number of trees which consume CO₂ is reduced. Human activities, thus, contribute to the accumulation of CO₂ in the atmosphere. CO₂ traps heat and does not allow it to escape into space. As a result, the average temperature of the earth’s atmosphere is gradually increasing. This is called global warming.

Water Pollution

Water pollution is the contamination of water bodies such as lakes, rivers, oceans, and groundwater caused by human activities, which can be harmful to organisms and plants that live in these water bodies. It occurs when pollutants are discharged directly into water bodies without treating it first.

Causes of Water Pollution

There are many causes for water pollution but two general categories exist: direct and indirect contaminant sources. Direct sources include effluent outfalls from factories, refineries, waste treatment plants etc. that emits fluids of varying quality directly into urban water supplies. In the United States and other countries, these practices are regulated, although this doesn't mean that pollutants can't be found in these waters.

Indirect sources include contaminants that enter the water supply from soils/groundwater systems and from the atmosphere via rain water. Soils and groundwaters contain the residue of human agricultural practices (fertilizers, pesticides, etc.) and improperly disposed of industrial wastes. Atmospheric contaminants are also derived from human practices (such as gaseous emissions from automobiles, factories and even bakeries).

Contaminants can be broadly classified into organic, inorganic, radioactive and acid/base.

Effects of Water Pollution

The effects of water pollution are varied. They include poisonous drinking water, poisonous food animals (due to these organisms having bioaccumulated toxins from the environment over their life spans), unbalanced river and lake ecosystems that can no longer support full biological diversity, deforestation from acid rain, and many other effects. These effects are, of course, specific to the various contaminants.

Corrective Actions Required

Science provides many practical solutions to minimizing the present level at which pollutants are introduced into the environment and for remediating (cleaning up) past problems. All of these solutions come with some cost (both societal and monetary). In our everyday lives, a great deal can be done to minimize pollution if we take care to recycle materials whose production creates pollution and if we act responsibly with household chemicals and their disposal. Additionally, there are choices we make each day that also can affect the quantity of pollutants our actions will introduce into the environment.

Heavily packaged foods, for instance, contain boxes, cartons, bottles etc. made with polluting dyes, many of which are released from groundwater at municipal land fills. Whether we choose to drive to the corner store rather than walk or ride a bicycle will determine how much we personally contribute to acid and hydrocarbon emissions to the atmosphere (and ultimately to global fresh water supplies).

Potable Water & Purification of Water

Water which is suitable for drinking is called potable water. Various physical and chemical processes in the sewage treatment plants help to clean water before discharging it into water bodies. Similarly, municipal bodies treat the water before supplying it to households.

Water can be made safe for drinking:

• Water is filtered. This is a physical method of removing impurities. A popular household filter is a candle type filter.

• Many households use boiling as a method for obtaining safe drinking water. Boiling kills the germs present in the water.

• Chlorination is a commonly used chemical method for purifying water. It is done by adding chlorine tablets or bleaching powder to the water.

Water pollution: The contamination of water that changes in the physical, chemical and biological conditions of water is called water pollution. This makes water unfit for human consumption.

Whenever harmful substances such  as sewage, toxic chemicals, silt, etc., get  mixed with water, the water becomes  polluted. 

The substances that pollute  water are called water pollutants.

1.Many industries discharge harmful chemicals into rivers and streams, causing the pollution of water.

2.Use of pesticides and weedicides . These chemicals dissolve in water and are washed into water bodies from the fields. They also seep into the ground to pollute ground water.

3. The bacteria present in the faeces of mammals.

4. Throwing  untreated sewage directly into rivers.

Water which is suitable for drinking is called potable water.

water can be made 

safe for drinking:

1. By filtering water. A popular household filter is a candle type filter.
2. By boiling Water.Boiling kills the germs present in the water
3. Chlorination is a commonly used chemical method for purifying water.It is done by adding chlorine tablets or bleaching powder to the water

WHAT YOU HAVE LEARNT

1. Water pollution is the contamination of water by substances harmful to life.
2. Sewage, agricultural chemicals and industrial waste are some of the major contaminants of water.
3. Water which is purified and fit for drinking is known as potable water.
4. Water is a precious natural resource. We must learn to conserve it.

Air pollution is described as any change in the composition of  air either by physical or chemical methods so as to cause harmful effects on health.

The substances which contaminate the air are called air pollutants. 

Sources of Air Pollution are : 
1. Natural sources 2. Man-made (anthropogenic) sources.
Natural sources: Volcanic eruption, forest fire, sea salt sprays, biological decay, photochemical oxidation of terpenes oil , marshes, pollengrains, spores, etc.,

Man made sources : Industrial emissions, vehicles, aeroplanes, power stations and burning of fuels, etc.,

Mainly air pollution is caused due to burning of fuels to run vehicles, and from chimneys of factories and power stations.
The Green House Effect : Some of the infrared radiation from the earth passes through the atmosphere but most is absorbed and re-emitted in all directions by greenhouse gas molecules and clouds. This warms up the Earth’s surface and the lower atmosphere

Global Warming : CO2 is continuously being released because of human activities. On the other hand, area under forests is decreasing. Plants utilize CO2 from the atmosphere for photosynthesis, thereby decreasing the amount of CO2 in the air. Deforestation leads to an increase in the amount of CO2 in the air because the number of trees which consume CO2is reduced. Human activities, thus, contribute to the accumulation of CO2 in the atmosphere. 

CO2 traps heat and does not allow it to escape into space. As a result, the average temperature of the earth’s atmosphere is gradually increasing. This is called global warming.

Ozone layer is thinning due to the emission of pollutant into the

atmosphere. Holes caused in the ozonelayer allow the harmful UV rays to reach the earth.

Radioactivity: Radio active minerals present in the earth’s crust are the sources of radioactivity in the atmosphere.

Acid Rain : Oxides of nitrogen, sulphur, carbon produced by combustion of coal, petroleum, etc,. dissolve in atmospheric water vapour. They form their corresponding acids like nitric acid, sulphuric acid, etc., and reach the earth’s surface as acid rain.

Effects of acid rain

● It irritates eyes and skin of human beings.

● It inhibits germination and growth of seedlings.

● It changes the fertility of the soil, destroys plants and aquatic life.

● It causes corrosion of many buildings, bridges, etc.,

Control of air pollution :Air pollution can be minimized by the following methods:

1. Use of crude oil should be avoided and use of high quality fuels, unleaded petrol, bio-diesel and compressed natural gas(CNG) should be recommended.

2. Use of automobiles should be minimized.

3. Industrial smokes must be filtered before releasing into the atmosphere.

4. By planting more trees to get pure air (O2) and reduce the CO2 content of the environment.