Question 21
State the impact of green house gases on geographic, climatic and agricultural conditions.
Answer
Impact of green house gases on:
- Geographic conditions — Global warming increases melting of ice-caps which results in rising of sea levels causing coastal floating and erosion.
- Climatic conditions — Tropical regions experience more rainfall. Northern latitudes experience shorter and wetter winters.
- Agricultural conditions — Affects due to climatic changes:
- the life cycle of trees and survival and reproduction of plants.
- the soil fertility and amount of soil water retained in the soil.
Answer: Geographic conditions, Climatic conditions, Agricultural conditions
Key Concepts Covered
This question tests your understanding of the following concepts from the chapter Atmospheric Pollution: Question, Impact, Green, House, Gases, Geographic. These are fundamental topics in Chemistry that students are expected to master as part of the ICSE Class 9 curriculum.
A thorough understanding of these concepts will help you answer similar questions confidently in your ICSE examinations. These topics are frequently tested in both objective and subjective sections of Chemistry papers. We recommend revising the relevant section of your textbook alongside practising these solved examples to build a strong foundation.
How to Approach This Question
Read the question carefully and identify what is being asked. Break down complex questions into smaller parts. Use the terminology and concepts discussed in this chapter. Structure your answer logically — begin with a definition or key statement, then provide supporting details. Review your answer to ensure it addresses all parts of the question completely.
Key Points to Remember
- Balance chemical equations before solving numerical problems.
- Learn the periodic table trends and exceptions.
- Understand reaction mechanisms, not just outcomes.
- Use correct IUPAC nomenclature in your answers.
Practice more questions from Atmospheric Pollution — Chemistry, Class 9 ICSE
Chapter Overview: Atmospheric Pollution
This chapter examines the causes, effects, and prevention of atmospheric pollution. The atmosphere is composed of nitrogen (78%), oxygen (21%), argon (0.93%), carbon dioxide (0.04%), and trace amounts of other gases and water vapour. Air pollution occurs when harmful substances (pollutants) contaminate the atmosphere. Major air pollutants include carbon monoxide (CO), sulphur dioxide (SO2), nitrogen oxides (NOx), particulate matter, and chlorofluorocarbons (CFCs). Acid rain forms when SO2 and NOx dissolve in rainwater to form sulphuric acid and nitric acid. The greenhouse effect is the trapping of heat by gases like CO2, CH4, and N2O, leading to global warming. Ozone depletion is caused by CFCs breaking down the ozone (O3) layer in the stratosphere. Students must understand the sources of each pollutant, its harmful effects on health and environment, and measures to control pollution. This chapter connects chemistry concepts to real-world environmental issues.
Key Concepts
| Pollutant / Issue | Details |
|---|---|
| CO (Carbon Monoxide) | From incomplete combustion; binds to haemoglobin, reducing O2 transport |
| SO2 | From burning fossil fuels with sulphur; causes acid rain and respiratory problems |
| Acid Rain | SO2 + H2O → H2SO3; 2NO2 + H2O → HNO3 + HNO2; pH < 5.6 |
| Greenhouse Effect | CO2, CH4, N2O trap infrared radiation, warming Earth's surface |
| Ozone Depletion | CFCs release Cl atoms that destroy O3: Cl + O3 → ClO + O2 |
| Global Warming | Rise in Earth's average temperature due to enhanced greenhouse effect |
| Smog | Smoke + fog; photochemical smog contains O3, NO2, and organic compounds |
Must-Know Concepts
- Composition of clean air: N2 (78%), O2 (21%), Ar (0.93%), CO2 (0.04%)
- CO is a silent killer - colourless, odourless, and highly toxic
- Acid rain (pH < 5.6) damages buildings (especially marble: CaCO3 + H2SO4 → CaSO4 + H2O + CO2), kills aquatic life, and harms vegetation
- Greenhouse gases in order of impact: CO2 > CH4 > N2O > CFCs
- Montreal Protocol (1987) aims to phase out CFCs to protect the ozone layer
- Control measures: catalytic converters in vehicles, using clean fuels, afforestation, emission regulations
Greenhouse Effect vs Ozone Depletion
| Feature | Greenhouse Effect | Ozone Depletion |
|---|---|---|
| Cause | Excess CO2, CH4, N2O | CFCs and halons |
| Location | Lower atmosphere (troposphere) | Upper atmosphere (stratosphere) |
| Effect | Global warming, sea level rise | More UV radiation, skin cancer |
| Prevention | Reduce fossil fuel use, afforestation | Ban CFCs (Montreal Protocol) |
Important Diagrams to Practice
- Greenhouse effect diagram showing incoming solar radiation and trapped infrared radiation
- Acid rain formation cycle (from factory emissions to acid precipitation)
- Ozone layer depletion mechanism (CFC breakdown and ozone destruction cycle)
Common Mistakes
- Confusing greenhouse effect (lower atmosphere, warming) with ozone depletion (upper atmosphere, UV radiation)
- Saying the greenhouse effect is entirely bad (it is natural and essential; the problem is the enhanced effect)
- Calling CO2 a pollutant in all contexts (it is a natural atmospheric component; excess is the problem)
- Confusing ozone at ground level (harmful pollutant in smog) with stratospheric ozone (protective)
Scoring Tips
- For essay-type questions, organise into: causes → effects → prevention
- Include chemical equations wherever possible (acid rain formation, ozone destruction)
- Mention specific international agreements: Montreal Protocol, Kyoto Protocol, Paris Agreement
- Use specific data: normal rain pH = 5.6, acid rain pH < 5.6; CO2 level now ~420 ppm
Frequently Asked Questions
Is the greenhouse effect good or bad?
The natural greenhouse effect is essential - without it, Earth's average temperature would be about −18°C instead of the current +15°C. The problem is the enhanced greenhouse effect caused by human activities increasing CO2 and other greenhouse gases, leading to global warming.
Why is the ozone hole mainly over Antarctica?
The extreme cold of the Antarctic winter creates polar stratospheric clouds where CFCs accumulate. When spring sunlight returns, UV light breaks CFC molecules, releasing chlorine atoms that rapidly destroy ozone. One chlorine atom can destroy up to 100,000 ozone molecules.
How does acid rain damage buildings?
Acid rain reacts with marble and limestone (CaCO3) in buildings: CaCO3 + H2SO4 → CaSO4 + H2O + CO2. This dissolves the stone surface, causing the "stone cancer" effect. The Taj Mahal is a famous example of acid rain damage.