BiologyICSE Class 10 · Pollution

Greenhouse Effect, Global Warming, Acid Rain and Ozone Depletion, with Control Measures (ICSE Class 10)

Updated 16 October 2026 · Fact-checked

Greenhouse gases such as carbon dioxide and methane trap the earth's heat; extra amounts cause global warming. Sulphur dioxide and nitrogen oxides dissolve in rain to form acid rain, which corrodes buildings and harms lakes, soil and forests. Chlorofluorocarbons thin the ozone layer, letting in more ultraviolet rays. CNG, emission norms, social forestry and sewage treatment help control pollution.

Notice that sunlight gets in easily, but the greenhouse gas layer traps part of Earth's outgoing heat, warming the planet.

Illustration drawn for QuestionBuddy.

Understand Greenhouse Effect, Acid Rain and Ozone Depletion

1. Greenhouse effect and global warming.

Sunlight passes through the atmosphere and warms the earth. The warm earth gives out heat (infrared rays).
Greenhouse gases, mainly carbon dioxide (CO₂), methane (CH₄), nitrous oxide and chlorofluorocarbons (CFCs), let sunlight in but trap part of this outgoing heat, like the glass of a greenhouse. This is the greenhouse effect.
The natural greenhouse effect is useful: without it the earth's average temperature would be about −18 °C instead of about 15 °C.
Human activities add extra greenhouse gases: burning coal, oil and gas (CO₂), deforestation (fewer trees to absorb CO₂), paddy fields, cattle and garbage dumps (methane). More heat is trapped and the average temperature rises: global warming.
Effects: melting of glaciers and polar ice, rise in sea level (flooding of coasts and islands), changes in rainfall, more floods and droughts, crop failures, spread of some diseases, loss of species. Long-term changes of this kind are called climate change.

2. Acid rain.

Sulphur dioxide (SO₂) from burning coal and oil in industries and power plants, and nitrogen oxides from vehicle engines, dissolve in rainwater to form sulphuric acid and nitric acid.
Normal rain is slightly acidic (pH about 5.6) because it dissolves a little CO₂; rain with a lower pH is called acid rain. Each fall of 1 in pH means the rain is 10 times more acidic.
The gases can travel hundreds of kilometres with the wind, so acid rain may fall far from the source.
Effects: corrosion of buildings, marble monuments, statues and metal structures; damage to leaves and forests; acidification of lakes and rivers (fish and their eggs die); leaching of nutrients from soil, lowering fertility.

3. Ozone layer depletion.

Ozone (O₃) high in the atmosphere forms a layer that absorbs harmful ultraviolet (UV) rays from the sun. Near the ground, ozone is a poisonous pollutant; high up, it is a shield.
Chlorofluorocarbons (CFCs), used in refrigerators, air conditioners, aerosol sprays and fire extinguishers, are very stable. They drift up to the ozone layer, where UV rays break them down and release chlorine, which destroys ozone; one chlorine atom can break down many ozone molecules.
Effects of more UV: skin cancer, cataract (eye damage), weaker immunity, damage to crops and to plankton in the sea.
Control: in 1987, under the United Nations Environment Programme, countries agreed first to freeze and then to cut CFC production; CFC-free refrigerators are now made.

4. Measures to control pollution (syllabus list).

Measure	How it helps
Unleaded petrol / CNG (compressed natural gas)	no lead in exhaust; CNG burns cleaner, with far less smoke and soot
Switching off engines at traffic signals	no fuel burnt while waiting; less exhaust
Social forestry	planting trees on common land; trees absorb CO₂ and dust and reduce noise
Sewage treatment plants	sewage is treated before it reaches rivers
Ban on polythene and plastics	less non-biodegradable waste choking drains and soil
Organic farming	manure and natural pest control instead of chemicals
Euro / Bharat Stage (BS) norms	legal limits on vehicle emissions; BS-VI applies across India from April 2020

5. Swachh Bharat Abhiyan. A national campaign for a Clean India, launched on 2 October 2014. Its objectives: end open defecation by building household and community toilets; scientific management of solid and liquid waste; keep streets, roads and public places clean; and change people's habits through awareness of sanitation and hygiene.

Greenhouse Effect, Acid Rain and Ozone Depletion: key facts

Cause and effect: Greenhouse effect CO₂, methane, nitrous oxide, CFCs trap heat
Acid rain SO₂ and nitrogen oxides form sulphuric and nitric acids
Ozone depletion chlorine from CFCs destroys ozone; One gas list for each problem.
Effects: Global warming melting ice, rising sea level, changing rainfall
Acid rain corroded monuments, dead fish, leached soil, damaged forests
More UV skin cancer, cataract, weak immunity; Give specific effects.
Control measures: Unleaded petrol/CNG
Engines off at signals
Social forestry
Sewage treatment plants
Ban on polythene
Organic farming
Euro/Bharat Stage norms; Swachh Bharat: toilets, waste management, clean public places.
Expansions: CFC chlorofluorocarbon
CNG compressed natural gas
BS Bharat Stage; Learn them exactly.

Greenhouse effect	CO₂, methane, nitrous oxide, CFCs trap heat
Acid rain	SO₂ and nitrogen oxides form sulphuric and nitric acids
Ozone depletion	chlorine from CFCs destroys ozone

Global warming	melting ice, rising sea level, changing rainfall
Acid rain	corroded monuments, dead fish, leached soil, damaged forests
More UV	skin cancer, cataract, weak immunity

CFC	chlorofluorocarbon
CNG	compressed natural gas
BS	Bharat Stage

How to answer Greenhouse Effect, Acid Rain and Ozone Depletion questions

Keep the three global problems apart: each has its own gases and its own effects.

1Identify the problem from the clue: trapped heat (greenhouse), acids in rain (acid rain), more UV (ozone depletion).
2Name the gases correctly: CO₂ and methane; SO₂ and nitrogen oxides; CFCs.
3Give specific effects, such as corrosion of marble monuments or skin cancer, not 'harms environment'.
4For control, choose the syllabus measure that removes that pollutant at its source.
5For Swachh Bharat, give objectives (toilets, waste management, cleanliness, awareness), not anti-smoke measures.
6For pH questions, remember that each unit lower is 10 times more acidic.

Greenhouse Effect, Acid Rain and Ozone Depletion in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

A car parked in the sun

Suppose a car is left with its windows shut in the afternoon sun. When you open it, the inside is much hotter than the air outside.

How is this like the greenhouse effect?

Try it first, then show the solutionSolution

Sunlight passes through the glass and warms the seats.
The warm seats give out heat that cannot easily pass back out through the glass.
Greenhouse gases act like the glass, letting sunlight in but trapping the earth's heat.

Answer: The glass traps heat as greenhouse gases do.

Memory hook: Light gets in, heat can't get out.

Scrapping an old refrigerator

Imagine your family replaces a very old refrigerator, and the scrap dealer is told to recover the gas from its cooling pipes rather than cut them open.

Why does this matter?

Try it first, then show the solutionSolution

Old refrigerators often contain CFCs.
Released CFCs drift up to the ozone layer, where their chlorine destroys ozone.
Thinner ozone lets more UV reach the earth, raising the risk of skin cancer and cataract.

Answer: To stop CFCs escaping and damaging the ozone layer.

Memory hook: Keep the CFCs in the pipe, keep the ozone in the sky.

Tricks to remember Greenhouse Effect, Acid Rain and Ozone Depletion

Short memory aids. Say each one aloud once, then use it on a question the same day.

Three problems, three gas sets
Greenhouse: 'CO₂ and Cows' (methane). Acid rain: 'SO-NO'. Ozone: 'CFCs Chew'.
Use it when: Naming the right gases.
Up good, down bad
Ozone up high shields; ozone near the ground poisons.
Use it when: Ozone questions.
One pH step, ten times
pH 4.6 is ten times as acidic as pH 5.6.
Use it when: Comparing acid rain samples.

Greenhouse Effect, Acid Rain and Ozone Depletion: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Not a greenhouse gas · 1 mark · MCQBoard level

Which of the following is NOT a greenhouse gas?
(a) carbon dioxide
(b) methane
(c) nitrogen
(d) chlorofluorocarbons

Try it first, then show the solutionSolution

Nitrogen, the main gas of the air, does not trap heat; the others do.

Answer: (c) nitrogen

Example 2: Greenhouse effect versus global warming · 2 marks · Short answerBoard level

Distinguish between the greenhouse effect and global warming. Is the greenhouse effect harmful?

Try it first, then show the solutionSolution

Greenhouse effect: the trapping of the earth's heat by gases such as CO₂ and methane; it is natural and keeps the earth warm enough for life (about 15 °C instead of about −18 °C). (1)
Global warming: the rise in the earth's average temperature because human activities have added extra greenhouse gases. The natural effect is useful; only its increase is harmful. (1)

Answer: The natural greenhouse effect is useful; global warming is the harmful rise caused by extra gases.

Example 3: How acidic is the rain? · 3 marks · Short answerHarder board level

Normal rain has a pH of about 5.6. Suppose a sample of rain in an industrial town has a pH of 4.6.
(a) Why is even normal rain slightly acidic?
(b) How many times more acidic is the sample than normal rain?
(c) Name the two acids mainly responsible.

Try it first, then show the solutionSolution

(a) Rain dissolves a little carbon dioxide, forming weak carbonic acid. (1)
(b) The pH is 1 unit lower, so it is 10 times more acidic. (1)
(c) Sulphuric acid (from SO₂) and nitric acid (from nitrogen oxides). (1)

Answer: (a) Dissolved CO₂ (b) 10 times (c) Sulphuric and nitric acids

Example 4: Rising carbon dioxide · 3 marks · Short answerHarder board level

Suppose the CO₂ in the air rose from about 280 parts per million before factories were common to about 420 parts per million today.
(a) Find the percentage increase.
(b) Give two human activities responsible.
(c) State one consequence of this rise.

Try it first, then show the solutionSolution

(a) (420 − 280) ÷ 280 × 100 = 50%. (1)
(b) Burning fossil fuels (coal, petrol, diesel) and cutting down forests. (1)
(c) More heat is trapped: global warming, with melting glaciers and rising sea level. (1)

Answer: (a) 50% (b) Burning fossil fuels; deforestation (c) Global warming

Example 5: Ozone: shield or poison? · 2 marks · Short answerHarder board level

Ozone high in the atmosphere is called a protective shield, yet ozone near the ground is treated as a pollutant. Explain both statements.

Try it first, then show the solutionSolution

High up, the ozone layer absorbs most of the sun's harmful ultraviolet rays, protecting living things from skin cancer and cataract. (1)
Near the ground, ozone is breathed in; it is poisonous and irritates the lungs and eyes, and damages plants. (1)

Answer: Up high it absorbs UV; at ground level it is a poisonous gas.

Example 6: Case study: choosing the right measure · 4 marks · Case-basedHOTS / competency

A city council lists four problems: (a) acid rain caused mainly by traffic; (b) a river turning foul below the city's drains; (c) drains choked by plastic bags in the monsoon; (d) pesticide residues found in vegetables from nearby farms. Choose one syllabus control measure for each and say how it helps.

Try it first, then show the solutionSolution

(a) CNG/unleaded fuel and Bharat Stage emission norms: less nitrogen oxide and sulphur in exhaust. (1)
(b) Sewage treatment plants: sewage is treated before it enters the river. (1)
(c) Ban on polythene and plastics: less non-biodegradable waste in drains. (1)
(d) Organic farming: manure and natural pest control replace chemical pesticides. (1)

Answer: (a) CNG/BS norms (b) Sewage treatment plants (c) Ban on polythene (d) Organic farming

Where students lose marks in Greenhouse Effect, Acid Rain and Ozone Depletion

The slips examiners see most often, and what to write instead.

Mistake: Vague effects of acid rain
CISCE examiners' comments, 2025 Q4(iv): candidates gave vague responses like 'pollution' or 'harms plants' instead of specific effects such as corrosion of monuments or leaching of nutrients.
Wrong working
Acid rain harms plants and causes pollution.
Right working
Acid rain corrodes marble monuments and leaches nutrients from the soil.
Do this: Name the object harmed and how.
Usually costs: 1 mark each.
Mistake: Wrong expansions of CFC and CNG
CISCE examiners' comments, 2025 Q7(iv): candidates expanded CFC as 'compressed fluorocarbons', confused CNG with LPG, or invented terms like 'Carbon Neutral Gas'.
Wrong working
CFC: compressed fluorocarbon; CNG: carbon neutral gas.
Right working
CFC: chlorofluorocarbon; CNG: compressed natural gas.
Do this: Learn each expansion word for word.
Usually costs: 1 mark each.
Mistake: Pollution-control measures given as Swachh Bharat objectives
CISCE examiners' comments, 2024 Q4(iv): candidates listed measures to prevent air pollution instead of objectives; 2025 Q8(iii): they wrote vague objectives like 'to keep clean' without linking them to sanitation or waste disposal.
Wrong working
Objective: use CNG vehicles; to keep clean.
Right working
Objectives: end open defecation by building toilets; manage solid and liquid waste; keep streets and public places clean.
Do this: Objectives are about sanitation, toilets and waste.
Usually costs: 1 mark each.

Exam tips

Write the gases for each problem: CO₂/methane, SO₂/nitrogen oxides, CFCs.
Say that the natural greenhouse effect is useful; only its increase causes global warming.
Quote control measures in the syllabus wording.
For Swachh Bharat, mention toilets and waste management.

Practice questions on Greenhouse Effect, Acid Rain and Ozone Depletion

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
Which of these gases is both a greenhouse gas and a cause of ozone layer depletion?
(a) methane
(b) chlorofluorocarbons
(c) sulphur dioxide
(d) nitrogen
Hint
Refrigerators and aerosol sprays.
Answer
(b) chlorofluorocarbons
Q2 · 2 marks · Very short answerBoard level
Name one human source each of (a) carbon dioxide and (b) methane in the atmosphere.
Hint
Fuels; farms.
Answer
(a) Burning coal, petrol or diesel (or deforestation). (b) Paddy fields, cattle or rotting garbage.
Q3 · 1 mark · Very short answerBoard level
Why is unleaded petrol better for health than leaded petrol?
Hint
What came out of the exhaust?
Answer
Leaded petrol releases lead, a poisonous heavy metal, in the exhaust; it harms the nervous system, especially in children. Unleaded petrol does not.
Q4 · 2 marks · Short answerHarder board level
Give two ways in which global warming can raise the sea level.
Hint
Ice and water both respond to heat.
Answer
Glaciers and polar ice on land melt and their water flows into the sea; sea water itself expands as it warms.
Q5 · 2 marks · Short answerHarder board level
Rain falling on a town 300 km from the nearest industrial area is found to be acidic, though the town has no factories. Explain.
Hint
Wind.
Answer
Sulphur dioxide and nitrogen oxides from distant industries and vehicles are carried long distances by wind and dissolve in clouds, so the acids fall as rain far from their source.
Q6 · 2 marks · Short answerHarder board level
CFC use has been cut sharply since the late 1980s, yet ozone damage continued for years. Suggest two reasons.
Hint
CFCs are very stable.
Answer
CFCs are very stable and stay in the air for many years, slowly drifting up to the ozone layer; and each chlorine atom released can destroy many ozone molecules.
Q7 · 2 marks · Short answerHOTS / competency
Suppose a lake receives rain of pH 4.2 instead of normal rain of pH 5.6. About how many times more acidic is this rain? Which living things in the lake are harmed first, and why?
Hint
10 raised to the power of the difference.
Answer
10^1.4 ≈ 25 times more acidic. Fish eggs and young fish (and other small aquatic animals) are harmed first, because they are most sensitive to a fall in the pH of the water.
Q8 · 3 marks · Short answerHOTS / competency
A family starts cycling for short trips instead of using the car, and carries cloth bags instead of plastic ones. Link each change to a pollution problem in the syllabus.
Hint
Global and local problems.
Answer
Cycling burns no fuel: less CO₂ (global warming), less nitrogen oxide (acid rain) and less smoke and noise in the street. Cloth bags mean less non-biodegradable plastic waste choking drains and polluting soil.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Approximate average temperature of the earth without the natural greenhouse effect?Show answer
About −18 °C (instead of about 15 °C).
2.Two acids in acid rain?Show answer
Sulphuric acid and nitric acid.
3.Element released from CFCs that destroys ozone?Show answer
Chlorine.
4.Year of the UN agreement to control CFCs?Show answer
1987.
5.When was Swachh Bharat Abhiyan launched?Show answer
2 October 2014.

Greenhouse Effect, Acid Rain and Ozone Depletion: frequently asked questions

Is ozone depletion the cause of global warming?

No. They are separate problems. Ozone depletion lets more ultraviolet rays reach the earth; global warming is caused by extra greenhouse gases trapping heat. CFCs happen to cause both.

Is all rain acidic?

Slightly. Normal rain dissolves a little carbon dioxide and has a pH of about 5.6. Only rain with a lower pH, made more acidic by sulphur dioxide and nitrogen oxides, is called acid rain.

How much of Swachh Bharat Abhiyan does ICSE need?

Only a brief mention: that it is a national campaign for a Clean India, launched in 2014, centred on sanitation, toilets and waste management. Do not confuse its aims with air-pollution control measures.