Cambridge IGCSE0680

The atmosphere

Environmental Management 0680 Chapter Notes

What this chapter covers

The atmosphereAtmospheric pollution and its causesImpact of atmospheric pollutionManaging atmospheric pollution
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In this chapter

  1. 1The Atmosphere's Makeup and Layers
  2. 2The Natural Greenhouse Effect
  3. 3Acid Rain: Causes and Consequences
  4. 4Ozone Depletion vs. Enhanced Greenhouse Effect
  5. 5Strategies for Managing Air Pollution

1. The Atmosphere's Makeup and Layers

The Earth's atmosphere is a vital layer of gases held in place by gravity. It's densest at sea level and thins out with altitude. The air we breathe is a mixture of several gases. Nitrogen (N₂) is the most plentiful, making up about 78% of the atmosphere. Oxygen (O₂), essential for respiration, accounts for about 21%. Argon (Ar), an inert gas, makes up almost 1%. The remaining fraction includes variable gases like water vapour (H₂O), carbon dioxide (CO₂), and ozone (O₃), whose concentrations change with location and time. The atmosphere is structured into four main layers based on how temperature changes with altitude: 1. Troposphere: The lowest layer (0-12 km), where we live and where all weather happens. Temperature decreases with height. 2. Stratosphere: From 12-50 km. It contains the ozone layer, which absorbs harmful UV radiation from the sun, causing the temperature to increase with height. 3. Mesosphere: From 50-80 km. Temperature decreases again, reaching the coldest points in the atmosphere. 4. Thermosphere: Above 80 km. Temperature rises dramatically due to absorption of intense solar radiation.

Nitrogen (N₂): ~78%

Oxygen (O₂): ~21%

Argon (Ar): ~0.9%

Carbon Dioxide (CO₂): ~0.04%

Key term

Troposphere: The lowest layer of Earth's atmosphere, where all weather phenomena occur and where temperature generally decreases with altitude.

Examiner insight

Marks are awarded for knowing the correct order of the atmospheric layers and the corresponding temperature trend in each layer.

Common pitfall

Confusing the order of the atmospheric layers, or incorrectly assuming that temperature consistently decreases with altitude.

Fun fact

If the Earth were the size of an apple, the breathable part of the atmosphere would be thinner than its skin.

Worked example 14 marks

The following table shows the composition of dry air. Complete the table with the missing information. [4 marks]

  1. 1

    Step 1: Identify the most abundant gas. This is Nitrogen with the formula N₂ and abundance of 78.09%.

  2. 2

    Step 2: Identify the second most abundant gas, which is essential for respiration. This is Oxygen. Its formula is O₂ and its abundance is approximately 20.95%.

  3. 3

    Step 3: Identify the main inert gas. This is Argon. Its formula is Ar and its abundance is 0.93%.

  4. 4

    Step 4: Identify the key greenhouse gas used by plants. This is Carbon Dioxide. Its formula is CO₂ and its abundance is approximately 0.04% (or 0.03% as often quoted in older texts).

Worked example 24 marks

Draw a simple graph with 'Altitude (km)' on the y-axis and 'Temperature (°C)' on the x-axis. Sketch and label the temperature profile through the four main layers of the atmosphere. [4 marks]

  1. 1

    Step 1: Draw and label the axes. Y-axis: Altitude (km) from 0 to 100. X-axis: Temperature (°C) from -100 to 40.

  2. 2

    Step 2: In the first layer (Troposphere, 0-12 km), draw a line showing temperature decreasing from about 15°C at the surface to -60°C.

  3. 3

    Step 3: In the second layer (Stratosphere, 12-50 km), draw the line showing temperature increasing from -60°C to about 0°C. Label the 'Ozone Layer' in this section.

  4. 4

    Step 4: In the third and fourth layers (Mesosphere, 50-80 km and Thermosphere, 80km+), draw the line decreasing again to about -90°C and then increasing sharply.

Recap

  • The atmosphere is mostly Nitrogen (78%) and Oxygen (21%).
  • The four main layers from the ground up are Troposphere, Stratosphere, Mesosphere, and Thermosphere.
  • All weather occurs in the Troposphere.
  • The ozone layer, which absorbs UV radiation, is in the Stratosphere.
  • Temperature decreases in the Troposphere and Mesosphere, but increases in the Stratosphere and Thermosphere.

Quick check

  1. Name the most abundant gas in the Earth's atmosphere.1 mark
  2. In which atmospheric layer does all weather occur?1 mark

2. The Natural Greenhouse Effect

The natural greenhouse effect is a crucial process that keeps the Earth's surface warm enough to support life. The process works like this: 1. The Sun emits short-wave radiation (like visible light and UV) that passes through the atmosphere. 2. Some of this radiation is reflected, but most is absorbed by the Earth's surface, warming it up. 3. The warmed Earth radiates heat back out as long-wave radiation (infrared). 4. Greenhouse gases in the atmosphere, such as water vapour (H₂O), carbon dioxide (CO₂), and methane (CH₄), absorb some of this outgoing long-wave radiation. 5. This absorbed energy is then re-radiated in all directions, including back down to the Earth's surface, trapping heat like a blanket. This natural process keeps the global average temperature at about 15°C. Without it, the Earth would be a frozen -18°C.

Incoming radiation: Short-wave (from the Sun)

Outgoing radiation: Long-wave / Infrared (from the Earth)

Key Greenhouse Gases: H₂O (Water Vapour), CO₂ (Carbon Dioxide), CH₄ (Methane), N₂O (Nitrous Oxide)

Key term

Greenhouse Gas: A gas in the atmosphere that absorbs and emits long-wave (infrared) radiation, causing the greenhouse effect.

Examiner insight

Students who clearly differentiate between incoming short-wave radiation and outgoing long-wave radiation in their explanations score higher marks.

Common pitfall

Believing the greenhouse effect is entirely a bad thing. The natural greenhouse effect is vital for life; it is the 'enhanced' greenhouse effect caused by human activity that is a problem.

Fun fact

Venus has a runaway greenhouse effect, making its surface hot enough to melt lead (over 460°C), despite being further from the Sun than Mercury.

Worked example 14 marks

Explain how the natural greenhouse effect keeps the Earth warm. [4 marks]

  1. 1

    Step 1: State that the Sun radiates short-wave radiation which passes through the atmosphere and warms the Earth's surface.

  2. 2

    Step 2: Explain that the warmed Earth re-radiates this energy as long-wave (infrared) radiation.

  3. 3

    Step 3: Mention that greenhouse gases (e.g., CO₂ or methane) in the atmosphere absorb this outgoing long-wave radiation.

  4. 4

    Step 4: Conclude by stating that this trapped energy warms the lower atmosphere and the Earth's surface, maintaining a temperature suitable for life.

Recap

  • The Sun heats the Earth with short-wave radiation.
  • The Earth cools by giving off long-wave (infrared) radiation.
  • Greenhouse gases like CO₂ and H₂O trap some of this outgoing long-wave radiation.
  • This natural process is essential for keeping the planet warm enough for life to exist.

Quick check

  1. Name the two most significant natural greenhouse gases.2 marks
  2. Does the greenhouse effect involve trapping incoming short-wave or outgoing long-wave radiation?1 mark

3. Acid Rain: Causes and Consequences

Acid rain is a broad term for precipitation—rain, snow, fog—that has become acidic from atmospheric pollutants. Normal rain is slightly acidic (pH ~5.6) due to dissolved CO₂, but acid rain has a lower pH, typically between 4.2 and 4.4. It forms when primary pollutants, mainly sulfur dioxide (SO₂) and nitrogen oxides (NOx), are released into the atmosphere. The main sources are the burning of fossil fuels in power stations (for SO₂) and vehicle exhausts (for NOx). In the atmosphere, these gases react with water, oxygen, and other chemicals to form sulfuric acid (H₂SO₄) and nitric acid (HNO₃). These secondary pollutants can be carried long distances by wind before falling as acid rain. The impacts are severe: it acidifies lakes and rivers, killing fish and other aquatic life; it damages forests by removing essential nutrients from the soil and harming leaves; and it corrodes buildings and statues made of limestone or marble.

Sulfur Dioxide Source: S (in fuel) + O₂ → SO₂

Nitrogen Oxide Source: N₂ + O₂ → 2NO (at high temp, e.g., in engines)

Acid Formation (simplified): SO₂ + H₂O → H₂SO₃ (Sulfurous Acid)

Acid Formation (simplified): 2NO₂ + H₂O → HNO₃ + HNO₂ (Nitric and Nitrous Acid)

Key term

Acid Rain: Precipitation that is unusually acidic (low pH) due to contamination by pollutants like sulfur dioxide and nitrogen oxides.

Examiner insight

Examiners look for specific sources of pollutants (e.g., coal power stations for SO₂) and specific, explained impacts (e.g., leaching of toxic aluminium from soil into lakes).

Common pitfall

Thinking acid rain is acidic enough to cause immediate burns to skin. Its damage is environmental and occurs over long periods.

Fun fact

Some of the acid rain that falls in Scandinavia originates from industrial pollution produced in the UK and Germany, highlighting its transboundary nature.

Worked example 15 marks

Explain the formation of acid rain and describe two of its environmental impacts. [5 marks]

  1. 1

    Step 1 (Formation): State that acid rain is caused by sulfur dioxide (SO₂) and nitrogen oxides (NOx) released from burning fossil fuels.

  2. 2

    Step 2 (Formation): Explain that these gases react with water vapour in the atmosphere to form sulfuric and nitric acids.

  3. 3

    Step 3 (Formation): Mention that these acids then fall to the ground as acid rain.

  4. 4

    Step 4 (Impact 1): Describe one impact, for example, the acidification of lakes, which can kill fish and other aquatic organisms.

  5. 5

    Step 5 (Impact 2): Describe a second impact, such as damage to forests by leaching essential nutrients from the soil or damaging leaves.

Recap

  • Acid rain is caused by sulfur dioxide (SO₂) and nitrogen oxides (NOx).
  • The main sources of these pollutants are power stations and vehicle exhausts.
  • The pollutants react with atmospheric water to form sulfuric and nitric acid.
  • Impacts include killing aquatic life, damaging forests, and corroding buildings.
  • Pollutants can travel long distances, causing a transboundary pollution problem.

Quick check

  1. Name the two primary pollutants responsible for acid rain.2 marks
  2. State one major source of sulfur dioxide pollution.1 mark

4. Ozone Depletion vs. Enhanced Greenhouse Effect

It is crucial not to confuse ozone depletion and the enhanced greenhouse effect. They are two separate environmental problems that occur in different parts of the atmosphere and have different causes and effects.

Ozone Depletion:

  • Where? Occurs high up in the Stratosphere.
  • What? The thinning of the ozone layer (O₃).
  • Cause? Primarily caused by man-made chemicals called Chlorofluorocarbons (CFCs), previously used in refrigerators and aerosols.
  • Mechanism? CFCs release chlorine atoms in the stratosphere, which act as catalysts to break down ozone molecules.
  • Consequence? A thinner ozone layer allows more harmful ultraviolet (UV-B) radiation from the sun to reach the Earth's surface.
  • Impact? Increased risk of skin cancer, cataracts, and damage to crops and marine life.

Enhanced Greenhouse Effect (Global Warming):

  • Where? Occurs lower down in the Troposphere.
  • What? The trapping of excess heat.
  • Cause? An increase in the concentration of greenhouse gases like carbon dioxide (CO₂) from burning fossil fuels and methane (CH₄) from agriculture.
  • Mechanism? These gases are very effective at absorbing outgoing long-wave (infrared) radiation from the Earth, preventing it from escaping to space and re-radiating it back to Earth.
  • Consequence? The average temperature of the Earth's atmosphere and oceans increases (global warming).
  • Impact? Climate change, including rising sea levels, more extreme weather events, and shifts in ecosystems.

Ozone Depletion (simplified): Cl + O₃ → ClO + O₂

Greenhouse Gases: CO₂, CH₄, N₂O, CFCs

Key term

CFCs (Chlorofluorocarbons): Man-made chemical compounds that are the primary cause of ozone depletion in the stratosphere.

Examiner insight

A table comparing the two phenomena is a highly effective way to structure an answer. Examiners specifically reward clear distinctions between the locations, pollutants, radiation types, and effects.

Common pitfall

The single biggest mistake is confusing the two issues, often by thinking the ozone hole traps heat or causes global warming. It does not; it lets in UV radiation.

Fun fact

The 'ozone hole' isn't a literal hole but a severe seasonal thinning of the ozone layer over Antarctica.

Worked example 16 marks

Complete the table to compare the enhanced greenhouse effect and ozone depletion. [6 marks]

  1. 1

    Row 1 (Type of radiation involved): Enhanced greenhouse effect involves trapping outgoing long-wave/infrared radiation. Ozone depletion involves allowing more incoming short-wave/UV radiation.

  2. 2

    Row 2 (Atmospheric layer): Enhanced greenhouse effect occurs in the Troposphere. Ozone depletion occurs in the Stratosphere.

  3. 3

    Row 3 (Pollutant gas): Enhanced greenhouse effect is caused by gases like CO₂ and CH₄. Ozone depletion is caused by CFCs.

  4. 4

    Row 4 (Action of pollutant): Greenhouse gases absorb infrared radiation. CFCs catalytically destroy ozone molecules.

  5. 5

    Row 5 (Main impact): Enhanced greenhouse effect leads to global warming/climate change. Ozone depletion leads to increased UV exposure, causing skin cancer/cataracts.

  6. 6

    Row 6 (International agreement): Enhanced greenhouse effect is addressed by the Paris Agreement/Kyoto Protocol. Ozone depletion is addressed by the Montreal Protocol.

Recap

  • Ozone depletion happens in the stratosphere and lets in more UV radiation.
  • The enhanced greenhouse effect happens in the troposphere and traps more heat (infrared radiation).
  • Ozone depletion is caused by CFCs.
  • The enhanced greenhouse effect is caused by gases like CO₂ and methane.
  • The Montreal Protocol successfully tackled ozone depletion; the Paris Agreement addresses climate change.

Quick check

  1. Which problem is caused by CFCs?1 mark
  2. Which layer of the atmosphere is warmed by the enhanced greenhouse effect?1 mark

5. Strategies for Managing Air Pollution

Managing air pollution requires action at all levels, from international cooperation to individual choices. Strategies can be grouped by scale:

1. International Level: Global problems require global solutions. International agreements bring countries together to commit to targets.

  • Montreal Protocol (1987): An incredibly successful treaty that phased out the production and use of CFCs to protect the ozone layer.
  • Paris Agreement (2015): A framework for countries to reduce greenhouse gas emissions to limit global warming.

2. National & Local Level: Governments use a mix of legislation and technology.

  • Legislation: Setting legal limits on the amount of pollutants that can be released from factories, power plants, and vehicles.
  • Technology: Requiring the use of pollution-reducing devices. For example, catalytic converters in car exhausts convert toxic gases (like carbon monoxide and nitrogen oxides) into less harmful substances. Flue-gas desulfurisation (FGD or 'scrubbers') in power station chimneys removes SO₂ before it enters the atmosphere.
  • Economic Policies: 'Carbon taxes' make pollution more expensive, while subsidies encourage investment in renewable energy (solar, wind, hydro).
  • Infrastructure: Investing in public transport to reduce the number of cars on the road.

3. Individual Level: Personal choices collectively make a big difference.

  • Reduce, Reuse, Recycle: Consuming less reduces the energy needed for manufacturing.
  • Energy Conservation: Using less electricity at home reduces demand on power stations.
  • Transport Choices: Walking, cycling, or using public transport instead of driving a car.
  • Dietary Choices: Reducing consumption of meat, particularly beef, can lower methane emissions from agriculture.

Key term

Catalytic Converter: An exhaust emission control device that converts toxic gases and pollutants in exhaust gas from an internal combustion engine into less-toxic pollutants.

Examiner insight

Examiners reward answers that provide specific, named examples of management strategies at different scales and can explain the mechanism by which they reduce pollution.

Common pitfall

Giving vague answers like 'stop polluting' or 'use less energy'. Answers must be specific, naming a strategy and explaining how it works.

Fun fact

In 2020, due to global lockdowns during the COVID-19 pandemic, levels of nitrogen dioxide pollution fell by as much as 60% in some major cities, showing how quickly air quality can improve when emissions are cut.

Worked example 16 marks

Describe three strategies that can be used to reduce atmospheric pollution, giving one example at a national, one at an international, and one at an individual level. [6 marks]

  1. 1

    Step 1 (International): Name and describe an international agreement. For example, the Montreal Protocol, which was an international treaty to phase out ozone-depleting substances like CFCs.

  2. 2

    Step 2 (International): State its purpose - to allow the ozone layer to recover.

  3. 3

    Step 3 (National): Name and describe a national-level strategy. For example, governments can pass laws requiring cars to be fitted with catalytic converters.

  4. 4

    Step 4 (National): Explain what it does - converts toxic exhaust gases like nitrogen oxides into harmless nitrogen and oxygen.

  5. 5

    Step 5 (Individual): Describe an individual action. For example, a person can choose to use public transport instead of driving a car.

  6. 6

    Step 6 (Individual): Explain how this helps - it reduces the amount of fossil fuels being burned and therefore cuts emissions of CO₂ and NOx.

Recap

  • Pollution can be managed at international, national, and individual levels.
  • The Montreal Protocol is a successful international treaty that tackled ozone depletion.
  • National strategies include laws, promoting renewable energy, and using technology like catalytic converters.
  • Flue-gas desulfurisation 'scrubs' sulfur dioxide from power station emissions.
  • Individual actions like saving energy and using public transport are also important.

Quick check

  1. What international agreement was signed to phase out CFCs?1 mark
  2. Name one technology used to reduce pollution from a coal-fired power station.1 mark

End-of-chapter exercise

Test yourself on the whole chapter. Work through these before moving on.

  1. List the three most abundant gases in the Earth's dry atmosphere, in order of abundance, and state their approximate percentages.3 marks
  2. Name the four main layers of the atmosphere in order, starting from the Earth's surface.4 marks
  3. Explain why temperature increases with altitude in the stratosphere.3 marks
  4. Describe two ways in which agricultural practices can cause air pollution.4 marks
  5. Explain the formation of photochemical smog in urban areas, naming at least one primary and one secondary pollutant involved.4 marks
  6. Suggest four reasons why many people are concerned about the enhanced greenhouse effect and rising global temperatures.4 marks
  7. Explain how a catalytic converter fitted to a car exhaust helps to reduce atmospheric pollution. Name one pollutant it removes.3 marks
  8. Compare and contrast the causes and environmental impacts of acid rain and ozone depletion.6 marks
  9. A graph shows that the atmospheric concentration of CO₂ was 320 ppm in 1965 and 420 ppm in 2025. (a) Describe the trend shown by this data. [1] (b) Calculate the percentage increase in CO₂ concentration over this 60-year period. Show your working. [2] (c) Suggest two human activities responsible for this trend. [2]5 marks
  10. 'International agreements are the only effective way to solve global atmospheric pollution.' To what extent do you agree with this statement? Justify your answer with examples.8 marks

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