Cambridge IGCSE Environmental Management (0680): The atmosphere and human activities – Study Guide

The atmosphere is the layer of gases that makes life on Earth possible, and it is also the part of the environment that human activities can change most visibly. This topic asks you to describe how the atmosphere is made up, then to explain three separate problems that people have caused in it: climate change, acid rain and ozone depletion. These three are often muddled in answers, so a large part of scoring well is keeping their causes, effects and solutions apart.

Where this fits in the course

In Cambridge IGCSE Environmental Management (0680) this topic sits alongside the topics on water, land and natural hazards, and it feeds the extended questions that ask you to evaluate a management strategy. It has four sub-topics: the atmosphere, climate change, acid rain and ozone depletion. Questions range from one-mark recall (name a gas) to longer responses where you weigh up one approach against another, so you need both facts and the ability to judge.

The atmosphere

Dry air is mostly nitrogen, roughly 78 per cent by volume, with about 21 per cent oxygen, just under 1 per cent argon and a tiny but important amount of carbon dioxide, around 0.04 per cent. Water vapour varies from place to place. Nitrogen is largely unreactive; oxygen supports respiration and combustion; carbon dioxide is used in photosynthesis and traps heat.

The lowest layer, the troposphere, holds most of the air and is where weather happens. Above it lies the stratosphere, which contains the ozone layer. Ozone absorbs much of the harmful ultraviolet radiation from the Sun, so the same gas is helpful high up and a pollutant at ground level.

Natural greenhouse effect

Some gases, including carbon dioxide, methane, water vapour and nitrous oxide, absorb heat radiated from the Earth’s surface and send some of it back down. This natural greenhouse effect keeps the average surface temperature high enough for liquid water and life. It is not the problem in itself; the problem is its enhancement.

Climate change

The enhanced greenhouse effect happens when human activities add extra greenhouse gases, so more heat is retained and the average global temperature rises.

Gas	Main human sources
Carbon dioxide	Burning coal, oil and gas; deforestation; cement production
Methane	Rice paddies, cattle digestion, landfill, leaks from gas extraction
Nitrous oxide	Nitrogen fertilisers, burning of biomass

Impacts

• Rising sea level, from thermal expansion of seawater and melting land ice, floods low-lying coasts and contaminates freshwater with salt.
• Changing rainfall patterns bring more frequent droughts in some regions and floods in others.
• Crop yields and growing seasons change, which affects food security.
• Habitats shift, and species that cannot move or adapt may decline.
• Heatwaves and some extreme weather events become more likely.

Management

Strategies fall into two groups. Mitigation reduces the cause: switching to renewable energy, improving energy efficiency, planting trees, reducing deforestation, and cutting methane from farming and waste. Adaptation copes with the effect: sea walls, drought-tolerant crops, water storage and early warning systems. Good answers say which group a measure belongs to and note its limits, such as cost, or the fact that countries must cooperate for mitigation to work.

Acid rain

Natural rain is slightly acidic, with a pH of about 5.6 because carbon dioxide dissolves in it. Acid rain has a lower pH than this. It forms when sulfur dioxide, released mainly by burning fossil fuels containing sulfur and by smelting metal ores, and nitrogen oxides, formed in vehicle engines and power stations at high temperature, dissolve in water droplets to make weak acids.

Impacts

• Lakes and rivers become acidic, harming fish eggs and invertebrates and reducing biodiversity.
• Soil loses nutrients and aluminium may be released, damaging tree roots; leaves can be damaged directly.
• Limestone and marble buildings and metal structures corrode faster.

Acid rain often falls far from where the gases were produced, because winds carry them, so it becomes an international problem.

Management

• Fit flue-gas desulfurisation (scrubbers) to power stations to remove sulfur dioxide.
• Use low-sulfur fuels or switch to renewables.
• Fit catalytic converters to vehicles to reduce nitrogen oxides.
• Add lime to acidified lakes as a short-term treatment of the effect.

Liming treats the symptom rather than the cause and has to be repeated, which makes it a good point for evaluation.

Ozone depletion

The ozone layer thins when chlorine and bromine from human-made chemicals reach the stratosphere. The main culprits are chlorofluorocarbons (CFCs), once widely used in aerosol sprays, refrigerators and foam packaging. Ultraviolet light breaks these molecules apart in the stratosphere, releasing chlorine atoms that destroy ozone repeatedly.

Thinner ozone lets more ultraviolet radiation reach the surface, which increases the risk of skin cancer and cataracts in people, and can harm plankton and crops.

The Montreal Protocol, agreed in 1987, committed countries to phase out CFCs and similar substances, and it is widely cited as an example of successful international cooperation. Replacement chemicals have been introduced, and the ozone layer is slowly recovering. Remember that ozone depletion is not the main cause of global warming, even though the two are often confused.

Worked example 1: a change in carbon dioxide

A monitoring station in a fictional region records carbon dioxide at 316 ppm in one decade and 389 ppm several decades later. Calculate the percentage increase.

1. Increase = 389 - 316 = 73 ppm.
2. Percentage increase = 73 / 316 x 100 = 23.1 per cent (to 3 significant figures).

If asked for the average annual rise over 45 years, divide 73 by 45 = 1.62 ppm per year.

Worked example 2: scrubbers and pH

A power station emits 9,600 tonnes of sulfur dioxide a year. Fitting scrubbers removes 92 per cent.

1. Removed = 9,600 x 0.92 = 8,832 tonnes.
2. Remaining emission = 9,600 - 8,832 = 768 tonnes per year.

A lake falls from pH 6.6 to pH 4.6. The pH scale is logarithmic, so each unit is a tenfold change in acidity. Two units down means 10 x 10 = 100 times more acidic.

Common mistakes

• Confusing the ozone hole with global warming, or saying that CFCs cause acid rain.
• Saying the greenhouse effect is harmful in itself; only the enhanced effect is a problem.
• Writing “pollution” or “the environment” without naming the gas, the process or the habitat affected.
• Listing management measures without stating what each one does to the cause or the effect.
• Forgetting that pH 5.6 is normal rain, not acid rain.

Exam technique

Command words matter. Describe asks what something is like; explain asks for a reason, so use “because” or “which leads to”; suggest asks you to apply knowledge to an unfamiliar situation; evaluate or assess needs a judgement supported by advantages and disadvantages. For a calculation, show your working and include units. For a management answer, name the measure, state how it works and add one limitation, and link each clearly to the problem it solves.

Check your understanding

1. Name the two most abundant gases in dry air and give their approximate percentages. (Nitrogen, about 78 per cent; oxygen, about 21 per cent.)
2. Distinguish the natural greenhouse effect from the enhanced greenhouse effect. (The natural effect keeps the Earth warm enough for life; the enhanced effect is the extra warming caused by added greenhouse gases from human activities.)
3. Give one mitigation and one adaptation response to climate change. (For example, renewable energy as mitigation; sea walls as adaptation.)
4. Which two gases are the main cause of acid rain, and where do they come from? (Sulfur dioxide from burning sulfur-containing fuels and smelting; nitrogen oxides from vehicle engines and power stations.)
5. Why is liming a lake only a partial solution? (It treats the effect, not the cause, and must be repeated.)
6. How does ozone depletion harm people? (More ultraviolet radiation reaches the surface, raising the risk of skin cancer and cataracts.)
7. A power station emits 5,000 tonnes of sulfur dioxide a year and scrubbers remove 90 per cent. What is emitted? (500 tonnes.)
8. Why is acid rain an international problem? (Winds carry the gases across borders, so it falls in countries that did not produce it.)

Frequently asked questions

What is the difference between the natural and enhanced greenhouse effect? The natural greenhouse effect is the warming caused by gases such as carbon dioxide, methane and water vapour absorbing heat radiated from the Earth, and it keeps the planet warm enough for life. The enhanced greenhouse effect happens when human activities add extra greenhouse gases, so more heat is trapped.

What is the pH of normal rain? Natural rain is slightly acidic, with a pH of about 5.6, because carbon dioxide dissolves in it. Rain at pH 5.6 is normal rain, not acid rain.

Why is acid rain an international problem? Winds carry the gases that cause acid rain across borders, so it often falls in countries far from where the gases were produced.

Is the ozone hole the same as global warming? No. Ozone depletion is caused by chlorine and bromine from human-made chemicals thinning the ozone layer, which lets more ultraviolet radiation reach the surface. Confusing it with global warming is a common mistake.

What did the Montreal Protocol do? The Montreal Protocol, agreed in 1987, committed countries to phase out CFCs and similar ozone-depleting substances.