Revision Notes Class 8 Chapter 18 Pollution of Air and Water

What is air?

Air is a combination of different gases that form the atmosphere of the Earth. The constituents of air are nitrogen (78%), oxygen (21%), water vapour, carbon dioxide and other gases such as helium, ozone, argon etc (0.04%) along with dust particles, pollens and spores. This constituent of air may vary on other planets. However, some planets do not have air. Space contains no air.

     Figure 1 Constituents of air

What is Air Pollution?

According to the World Health Organization, air pollution is defined as the presence of different substances in a certain concentration in the air that causes harm to human beings and the environment.

In other words, when the air gets contaminated due to harmful and unnecessary substances that can affect the living and nonliving things on the earth it is called air pollution.

                                    Figure 2 Pollution of Air due to industries

How does Air get polluted?

Air Pollutants: Any unwanted or harmful substance present in the air that decreases its quality and contaminates it is called air pollutants. For example, smoke is an air pollutant. Air pollutants can be classified into different categories based on their sources.

1. Indoor and Outdoor Air Pollutants
Indoor pollutants
These pollutants are generated indoors in houses, institutions, buildings or commercial facilities. Indoor air pollution may not severely impact people’s health but can certainly affect them in the long run. Different indoor pollutants are:

tobacco smoke

biological pollutants like pet hair, fungi, bacteria, pollens etc

building materials like lead and asbestos (asbestos can cause cancer)

gases such as carbon monoxide

                               Figure 3 Indoor Air Pollutants

What is indoor air quality (IAQ)?

Indoor air quality is defined as the quality of the air within houses, buildings and commercial structures. Low indoor air quality can lead to immediate effects such as irritation in the eyes, redness of eyes, headaches or dizziness. It may also lead to adverse effects in the long run such as the problem of asthma. Air purifiers are used in many houses and offices to ensure clean air in the surroundings.

Outdoor Pollutants

Outdoor air pollution refers to the contamination of the air in the open environment. Outdoor air pollutants generally arise from the burning of fossil fuels, smoke from industries and vehicles. They adversely affect the quality of the air and hence the whole environment of the earth. Different outdoor pollutants are:

a) carbon monoxide

b) nitrogen oxide

c) Sulphur Dioxide

d) hydrocarbons

Figure 4 Outdoor Air Pollution Sources

2. Primary and Secondary Air Pollutants

Depending upon their emission into the air, the air pollutants can be categorized as primary or secondary. Primary pollutants are the ones that are emitted directly in the environment. For example, harmful gases such as carbon monoxide, carbon dioxide, sulphur dioxide, nitrogen oxide etc, are emitted directly from industries and vehicles into the air.

Secondary Pollutants are the ones that get generated due to the reactions between various constituents of the year. For example, acid rain is a secondary pollutant. Nitrogen oxides react with the water vapour present in the air and form nitric acid.

Figure 5 Primary and Secondary Air Pollutants

Causes of Air Pollution

Air pollution from Natural Sources: sometimes forest fires or volcanic eruptions can lead to the release of an excess of smoke and dust in the atmosphere.

Burning of fossil fuels: coal and petroleum used in industries and vehicles when burnt release harmful substances in the air such as carbon monoxide, nitrogen oxides and sulphur dioxide.

Exhaust from factories: many industries release harmful substances like carbon dioxide, hydrocarbons and other harmful chemicals in the air which decrease its quality.

Agricultural activities: usage of insecticides, fertilizers and pesticides lead to release of chemicals in the air. Agricultural activities also lead to the release of ammonia in the atmosphere which is extremely hazardous for us.

Pollution due to households: paints, cleaning products, air conditioners, refrigerators and other appliances used in houses also contribute to air pollution. The air conditioners and refrigerators release chlorofluorocarbons that damage the ozone layer of the earth. Burning of wood and cow dung cakes in rural areas also leads to air pollution.

Mining activities: mining results in the release of a large amount of dust and chemicals in the air.

Effects of Pollutants on the Environment

Air pollution and the case study of the Taj Mahal

We know that air pollution can severely affect the environment. One great example of the harmful effects of air pollution can be viewed on the Taj Mahal, the most famous and beautiful tourist attraction of India.

The air pollution in that region has led to decolourization of the white marbles of the Taj Mahal.

       Figure 6 Effect of Air Pollution on Taj Mahal

Causes of air pollution in Agra and effects on the Taj Mahal

1. The main sources of pollutants in the air around Taj Mahal are the industries around Agra.

2. The Mathura oil refinery and other industries including automobiles, rubber processing and chemicals are releasing harmful substances in the air.

3. The major pollutants are Nitrogen dioxide and Sulphur Dioxide. These pollutants lead to acid rain in the Agra region.

4. When Nitrogen dioxide combines with water it forms nitric acid and when Sulphur Dioxide combines with water it forms sulphuric acid.

5. The rainwater which falls on the Taj Mahal leads to decay of the marble. This is also called ‘marble cancer’.

6. The Mathura oil refinery is a major source of suspended particulate matter (SPM) in the air around the Taj Mahal which is making the white marble look yellow in colour.

Steps were taken to reduce air pollution in the area near Taj Mahal

1. The industries are switching to clean fuels such as CNG and LPG to prevent air pollution and protect the monument.

2. Also, unleaded petrol should be used in automobiles to prevent harmful smoke from the vehicles near the Taj Mahal area.

The Greenhouse Effect

1. As the sun rays enter the earth’s atmosphere, some of the radiation gets reflected back into space while some of it is trapped inside the earth’s atmosphere.

2. This is possible because of certain greenhouse gases in the earth’s atmosphere which can trap the heat of the sun. For example, carbon dioxide, methane, nitrous oxide and water vapour can trap the sun’s radiation inside the earth. This phenomenon is called the greenhouse effect.

3. Due to this greenhouse effect, the earth has a stable temperature that can support the existence of life on it. The greenhouse effect provides the required warmth to the earth.

4. However, due to excess of carbon dioxide in the atmosphere, the greenhouse effect is becoming a serious trouble for the earth.

5. The excess of greenhouse gases leads to absorption of more heat inside the Earth which further leads to a gradual rise in the temperature of the Earth. This phenomenon of increased temperature of the earth is called global warming.

                            Figure 7 Greenhouse Effect

Sources of carbon dioxide on earth:

1. Human activities such as the burning of fossil fuels and industrial activities etc are causing a release of carbon dioxide in the atmosphere.

2. Cutting of forests imbalances the carbon dioxide and oxygen amounts in the air as plants take up the carbon dioxide from the environment and in return release oxygen. Therefore deforestation leads to increased presence of carbon dioxide in the atmosphere.

Effects of global warming

                                       Figure 8 Effects of Global Warming

Global warming leads to an increased temperature of the Earth which causes the melting of the glaciers and therefore increased sea levels. Hence, it results in flooding the areas around the sea.

It also leads to extreme weather conditions in different places of the earth.

Increased rainfall in different places has occurred due to the higher temperatures of the earth.

Extinction of species or loss of habitats is occurring due to global warming as the animals are not able to adapt to changing climatic conditions of the earth.

What is the Ozone Layer?

The earth’s atmosphere is covered with a layer of ozone gas all around.

This ozone gas prevents the dangerous ultraviolet rays of the sun from reaching the surface of the earth.

The ultraviolet rays of the sun if reach the earth’s surface can cause severe problems.

They can affect the plants, cause cancer in human beings, skin and eye diseases and can harm all other biotic and abiotic components of the earth.

Hence, the ozone layer has a significant role in the environment.

What is the ozone layer depletion?

Ozone layer can be termed as deterioration of the ozone layer due to the presence of harmful substances in the environment. The main cause for the depletion of the ozone layer is CFCs or Chlorofluorocarbons. They react with the ozone gas and form molecular oxygen.

                                    Figure 9 Ozone Layer Depletion

Prevention of Air Pollution

1. Switching to cleaner fuels like CNG and LPG can lead to decreased air pollution.

2. Generating awareness among people about air pollution and its harmful effects will encourage them to participate in preventing it.

3. Increasing the usage of solar energy, wind energy and hydropower.

4. Planting more and more trees around the cities in rural areas. India celebrates ‘Van Mahotsav’ in July every year where people come together and plant trees on a large scale.

5. Instead of burning dry leaves and other organic materials they should be dumped into compost.

6. Using gas stoves instead of burning coal or wood to cook food.

7. Sharing vehicles or using public transport to reduce the number of vehicles on the road and hence the air pollution.

8. Using eco-friendly paints and cleaning products for household and other buildings.

Water Pollution

Water is not only necessary for the existence of life on the earth but it is required to perform several days to day activities like cleaning, washing clothes, bathing, cooking etc.

Due to these activities, several substances get mixed up in water which makes it unsafe for further consumption.

This addition of biological, chemical and physical substances in water is called water pollution.

These substances contaminate water and make it unfit for consumption of human beings and animals are called water pollutants.

                           Figure 10 Sources of Water pollution

How water gets polluted?

A case study of Ganga River
Ganga is one of the most significant rivers of India. It flows through many towns, cities and villages of the northern, eastern and central India.

People living in these regions are dependent upon Ganga water for their livelihood as well as for their day-to-day needs.

But it has been found that Ganga is one of the 10 endangered rivers of the world according to the (WWF) World Wide Fund for Nature. This is because of its extreme pollution. The river has been called in dead at several places as it has no aquatic life there.

Causes of water pollution of Ganga

1. Various towns, villages and cities through which the Ganga River passes release untreated sewage water, garbage, dead bodies and other harmful substances into it.

2. The Ganga River flowing through Kanpur region in Uttar Pradesh is the most polluted part of this river. This is so because of the large population of Kanpur.

3. People use river water for bathing, cleaning, washing clothes and they even defecate in the river. From polythene bags to idols of Gods, flowers and garbage, people through several things in the river. All this leads to its pollution.

4. The flow of river Ganga near Kanpur region is slow which leads to more pollution of it in still water.

5. There are more than 5000 industries in Kanpur including leather, detergent, paint and Fertilizer Industries. All of these released toxic wastes in the river which leads to its pollution.

In order to prevent the river Ganga from getting polluted the Government of India had initiated the Ganga Action Plan in 1985. However, increased industries and growing population of India have damaged the river to use extend. Hence the Government of India has now started another initiative called the National Mission for Clean Ganga in 2016.

What is eutrophication?

Eutrophication is the presence of an excess of nutrients in the water, especially stagnant water.

Eutrophication mainly occurs due to the addition of chemicals in the water bodies.

As a result, a large number of algae and other plants start growing in water.

As they die, decomposers begin to rise in the water. These decomposers take up most of the oxygen of the water.

Hence, the lack of oxygen leads to the killing of aquatic animals in the water body.

                  Figure 11 Eutrophication

Potable Water

Drinking water or the water that is fit for consumption and food preparation is also called Potable water.

How is water purified?

In order to prevent water pollution, water from households, industries and other sources is treated in a sewage treatment plant and then it is released in the water bodies.

Also, water from the water bodies is treated before passing it on to the households and other industries to ensure that it is fit for the usage.

How water is made safe for drinking?

1. Filtration: it is a physical method of removing impurities from water. Many households use water purifiers that can filter water and make it safe for drinking.

2. Boiling: it kills the germs present in the water. Many people boil water before drinking it.​

3. Chlorination: Chlorine is a natural cleaning agent for water which makes it fit for the consumption. Often chlorine tablets are added in water to remove impurities from it.

How to prevent water pollution?

1. Industries should strictly adhere to the laws and do not dispose untreated sewage water into the rivers or any other water body directly.

2. More water treatment plants should be established near the industrial areas.

3. We should save water as much as we can, for example, we can make sure that there are no leaking taps in the houses.

4. We should reuse water if we can, for example, the water that we use for washing clothes can also be used for cleaning the house floors.

                                    Figure 12 Steps to Prevent Water Pollution