ICSE Class 9 Chemistry Chapter 10 Atmospheric Pollution

10 Atmospheric Pollution

Scope Of Syllabus

Acid Rain - composition, cause and its impact.

Sulphur in fossil fuels giving oxides of sulphur when burnt. High temperatures in furnaces and internal combustion engines produce oxides of nitrogen. (Equations to be included). Acid rain affects soil chemistry and water bodies.

Global Warming

Greenhouse gases-their sources and ways of reducing their presence in the atmosphere. (water vapour, carbon dioxide, methane and oxides of nitrogen)

Ozone Depletion

Formation of ozone - relevant equations.

Function in the atmosphere.

Destruction of the ozone layer - chemicals responsible for this to be named but reactions not required.

Important Points To Remember

1. The gaseous envelope surrounding the earth is called as atmosphere. The atmosphere extends about 50 km above the sea level.

2. The atmosphere of the earth may be divided into several distinct layers.

The Troposphere

The Stratosphere and the ozone layer

Troposphere - lowest portion of earth's atmosphere. It contains approximately 75% of earth's atmosphere more and 99% of its water vapour and aerosol.

Stratosphere is the second major layer of earth's atmosphere, just above the troposphere. It is situated between about 10 km and 50 km above the sea level.

3. Ozone layer absorbs 97-99% of sun's UV light, which is damaging the life on earth. It is mainly located in the lower portion of the stratosphere from approximately 13 to 40 km above the sea level.

4. The tropospheric pollution or the air pollution is caused by the following pollutants:

Gaseous air pollutants: This includes mainly oxides of sulphur, oxides of nitrogen, oxides of carbon, ozone, hydrogen sulphide etc.

Particulate air pollutants: This includes smoke, dust, fumes etc.

5. Sulphur dioxide is one of the major atmospheric pollutants.

6. Sulphur dioxide is added into our environment by various activities like by burning of sulphur containing fuels, by burning of oils and during the roasting of sulphide ore in metallurgy.

Teacher's Note

Air pollution from vehicle emissions and industrial burning is visible as smog in cities - we can see its direct impact on air quality and visibility on hazy days.

7. The presence of sulphur dioxide in the atmosphere badly affects the human physiology. It causes severe headache, nausea, vomiting and in some cases it can prove fatal.

8. Sulphur dioxide is oxidized by atmospheric oxygen to form sulphur trioxide which combines with water to form sulphuric acid. This acid gets washed down with the rain and causes acid rain.

\[2\text{SO}_2 + \text{O}_2 \longrightarrow 2\text{SO}_3\]

\[\text{SO}_3 + \text{H}_2\text{O} \longrightarrow \text{H}_2\text{SO}_4\]

The acid corrodes the limestone and metals of the buildings and bridges etc.

9. Oxides of nitrogen are another major air pollutants which are introduced into the atmosphere by the burning of the fossil fuels in internal combustion engines produces a very high temperature and thus nitrogen and oxygen of air combine to form nitric oxide.

\[\text{N}_2 + \text{O}_2 \longrightarrow 2\text{NO}\]

(Nitric oxide)

Nitric oxide further combines with atmospheric oxygen to form nitrogen dioxide.

\[2\text{NO} + \text{O}_2 \longrightarrow 2\text{NO}_2\]

Nitrogen dioxide combines with rain water and oxygen to form nitric acid which comes to the earth in the form of acid rain.

\[4\text{NO}_2 + 2\text{H}_2\text{O} + \text{O}_2 \longrightarrow 4\text{HNO}_3\]

10. Nitrogen dioxide is a major atmospheric pollutant and adversely effects the human beings, plants and animals. The adverse effects of NO₂ are as follows -

It causes irritation in mucous membrane.

Large quantities of NO₂ can lead to serious lung congestion and in same cases can prove fatal.

The presence of nitrogen dioxide severely damages the leaves of the plants.

Nitrogen dioxide in the presence of light oxidizes hydrocarbon leading to the formation of photo chemical smog which cause irritation in eyes, asthma attack and other respiratory tract infections.

11. Acid rain has a very adverse affect on the soil chemistry, the water bodies, buildings and the vegetation -

Acid rain removes the basic essential nutrients from the soil.

Acid rain increases the acidic character of the water bodies and thus the water becomes unfit for the survival of the aquatic animals like fishes.

Acid rain basically damages the leaves of the plants.

It has harmful effect on the sculptures monument and buildings made of limestone, marbles and metals.

12. Taj Mahal (one of the seven wonders of the world) made of marble which is chemically calcium carbonate is being corroded by the acid rain and if the emission of NO₂ and SO₂ are not stopped in the nearby refineries then it can give a very ugly look to the Taj Mahal.

\[\text{CaCO}_3 + 2\text{HNO}_3 \longrightarrow \text{Ca(NO}_3)_2 + \text{H}_2\text{O} + \text{CO}_2\]

\[\text{CaCO}_3 + \text{H}_2\text{SO}_4 \longrightarrow \text{CaSO}_4 + \text{H}_2\text{O} + \text{CO}_2\]

13. The rise in temperature of the earth's surface is called as global warming. It is caused due to the trapping of sun's radiation by carbon dioxide in the atmosphere. This process is called as greenhouse effect.

14. The gases which causes the greenhouse effect are called as greenhouse gases. Which includes carbon dioxide, methane, water vapour, ozone, chlorofluorocarbon, nitrous oxide etc.

15. The earth surface gets heated up by infrared radiations of the sun rays. Earth surfaces emits the infra red radiations and it escapes the earth's surface. During the process of emission some of the IR rays get absorbed by the greenhouse gases and thus it remains on the earth and these trapped radiations warm the surface of the earth and lower atmosphere.

Teacher's Note

Greenhouse gases trap heat like a blanket around Earth - think of how a car's interior heats up when parked in the sun with closed windows.

16. The various effects of global warming are -

It will lead to the melting of the glaciers and the polar ice caps which would lead to submerging of low lying coastal areas.

Global warming increases the water vapour in the atmosphere which will contribute further in increasing the temperature of the earth.

17. Ways of reducing the greenhouse gases in the atmosphere-

Afforestation-Plant more trees, save forests, increase green cover.

Minimum use of automobiles-use more of public transport, car pools, ride bicycles for shorter distances etc.

Burning of fossil fuels should be minimized.

18. Ozone is formed by the action of UV rays of the sun on oxygen.

\[3\text{O}_2 \xrightarrow{\text{UV rays}} 2\text{O}_3\]

19. Ozone prevents the harmful ultraviolet radiations to reach the earth.

20. Ozone layer protects the life on earth from harmful UV rays which would lead to several skin diseases.

21. Decrease of the ozone in the stratosphere is called as the depletion of the ozone layer or the destruction of the ozone layer.

22. The formation of the holes in the ozone layer causes the harmful UV rays to enter into the earth.

23. The main causes of the depletion of ozone layer are

Excessive use of chlorofluorocarbons. Flying of super sonic planes.

Teacher's Note

CFCs from old refrigerators and air conditioners can damage the ozone layer - which is why we now recycle these appliances properly.

Important Questions

Q1. Name the following:

A gas which contributes towards greenhouse effect.

Two gases which causes acid rain.

The oxide of nitrogen which causes greenhouse effect.

An allotrope of oxygen which causes greenhouse effect.

Another name of greenhouse effect.

Ans. Carbon dioxide

Nitrogen dioxide and sulphur dioxide

Nitrous oxide

Ozone

Global warming

Q2. Write balanced chemical equation for the formation of acid rain.

Ans. \[\text{N}_2 + \text{O}_2 \xrightarrow{\text{Thunder and lightning}} 2\text{NO}\]

\[2\text{NO} + \text{O}_2 \longrightarrow 2\text{NO}_2\]

\[4\text{NO}_2 + 2\text{H}_2\text{O} + \text{O}_2 \longrightarrow 4\text{HNO}_3\]

(Acid rain)

Q3. What are the causes for the destruction of ozone layer?

Ans. The major causes are

Excessive use of chlorofluorocarbon

Flying of supersonic planes.

Q4. What is the full form of CFC?

Ans. Chlorofluorocarbon.

Q5. Give equation for the formation of ozone in the atmosphere.

Ans. \[3\text{O}_2 \xrightarrow{\text{UV rays}} 2\text{O}_3\]

Q6. Fill in the blanks.

Ozone absorbs the harmful - rays coming from the sun.

Carbon dioxide enters into atmosphere due to -.

The rise in the average temperature of earth's surface is called -.

Taj Mahal is made up of - which is chemically -.

The particulate pollutants include -, -, -, -,

and -.

Ans. ultraviolet

burning

global warming

marble, calcium carbonate

dust, smoke, mist, fumes and spray

Q7. Define atmosphere.

Ans. The gaseous envelope surrounding the earth is called as atmosphere.

Q8. What are the ways of reducing greenhouse effect?

Ans. Afforestation - Plant more trees.

Minimum use of automobiles - use public transport.

Burning of fossil fuels should be minimized.

Deforestation should be stopped.

Q9. Define pollution.

Ans. Any undesirable change in our natural environment is called as pollution.

Q10. What is the main source of sulphur dioxide in atmosphere?

Ans. By the burning of fossil fuels.

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