Air Pollution and the Greenhouse Gases

What this lesson covers in the specification

Incandio is aligned to this specification. It is not published by, endorsed by or affiliated with Pearson, and it reproduces none of Pearson's wording — the statement numbers are given so you can check every lesson against your own copy.

• 4.12 — Biological consequences of air pollution by sulfur dioxide and carbon monoxide
• 4.13 — Water vapour, carbon dioxide, nitrous oxide, methane and CFCs as greenhouse gases
• 4.14 — How human activities contribute to greenhouse gases

Specification section 4(d) Human influences on the environment — also taught in The Carbon and Nitrogen Cycles, Global Warming and Deforestation, Water Pollution and Eutrophication.

1 · Understand it

No exam language yet. The only question this section answers is: do I actually understand what is happening?

Burning fuel releases several gases, and they cause harm in two completely different ways. Sulfur dioxide and carbon monoxide are POISONS — they damage the organisms that encounter them, near where they are released. The greenhouse gases do nothing of the kind: they are harmless to breathe and they act globally, by changing how much energy the Earth retains. Keeping those two mechanisms apart is most of what this page is for.

SULFUR DIOXIDE — a local poison that travels

1. It is released when fossil fuels containing sulfur impurities are burned, chiefly in power stations.
2. In the air it dissolves in water droplets and is oxidised, forming ACID RAIN — rain with a pH well below normal.
3. That rain acidifies lakes and rivers. Fish eggs fail to develop and fish die, so populations fall and some species disappear from affected waters entirely.
4. It damages trees directly, killing leaves and needles, and it also acidifies the soil.
5. Acidified soil dissolves aluminium ions out of the rock, which are toxic to plant roots and are washed into waterways where they damage fish gills.
6. It also leaches away mineral ions such as magnesium and calcium that plants need, so trees are weakened further.

One point makes sulfur dioxide politically difficult as well as biologically important: the rain falls wherever the wind takes it. Sulfur dioxide released in one country acidifies lakes hundreds of miles away in another, which is why acid rain became one of the first environmental problems to require international agreement rather than national law.

CARBON MONOXIDE — a poison that acts inside the body

1. It is produced by the INCOMPLETE combustion of fuels — burning with an insufficient supply of oxygen, as in a badly maintained boiler or a car engine.
2. It is colourless and has no smell, so it cannot be detected by the person breathing it.
3. In the lungs it diffuses into the blood and binds to HAEMOGLOBIN in red blood cells, in the place oxygen would occupy.
4. It binds far more strongly than oxygen does and is not readily released, so that haemoglobin is effectively out of action.
5. The blood therefore carries much less oxygen, so less reaches the tissues, and cells cannot respire aerobically at the rate they need.
6. The effects are headache, dizziness and unconsciousness, and at higher concentrations death.

Now the second problem, which is not a poisoning at all. The GREENHOUSE EFFECT is a natural and necessary process: certain gases in the atmosphere allow short-wavelength radiation from the Sun to pass through to the surface, but absorb the longer-wavelength radiation the warmed Earth emits back outwards, and re-radiate some of it downwards. Without it the Earth's mean surface temperature would be around −18 °C and it would be uninhabitable. The problem is not the greenhouse effect; it is that we are strengthening it.

Think of it like a blanket rather than a poison

A blanket does not warm you. It slows the rate at which the heat you are already producing escapes, so you end up warmer at the same rate of production. Add more blankets and you get warmer still, and it makes no difference whether the blankets are toxic — they are working by trapping, not by touching. That is why carbon dioxide can be entirely safe to breathe and still be the central problem: it is not doing anything to organisms directly, it is changing how much energy the whole planet keeps.

The greenhouse gases, and where the human contribution comes from

1. CARBON DIOXIDE — from burning fossil fuels in power stations, vehicles and industry, and from deforestation, which both releases carbon when trees are burned and removes the photosynthesis that would have absorbed it.
2. METHANE — from cattle and other livestock, which produce it during digestion; from rice paddy fields, where it is produced in waterlogged soil; and from decaying waste in landfill sites.
3. NITROUS OXIDE — from the use of nitrogen fertilisers on farmland, and from vehicle exhausts.
4. CFCs — from aerosols, refrigerants and older manufacturing, now largely banned by international agreement.
5. WATER VAPOUR — the most abundant greenhouse gas of all, and largely outside direct human control; its concentration rises as the atmosphere warms, which amplifies the warming caused by the others.

It is worth being precise about the biggest two, because the arithmetic is not obvious. Carbon dioxide dominates because of the sheer quantity released, not because each molecule is especially effective — methane traps far more heat per molecule but is released in much smaller amounts and breaks down in the atmosphere within a couple of decades, while carbon dioxide persists for centuries. Both quantity and persistence matter, and an answer naming only one of them has half the picture.

2 · Grade 9 Notes

A different job from the section above. You have already understood it; this is the precise set of things to LEARN — definitions to reproduce word for word, processes in order, equations with units, and the answers that score full marks.

The two kinds of harm — the distinction this page exists to establish

Statement 4.12 — how sulfur dioxide damages ecosystems, the chain to write

1. Sulfur dioxide is released when fossil fuels containing sulfur are burned.
2. It dissolves in water droplets in the air and is oxidised, forming acid rain.
3. Acid rain lowers the pH of lakes and rivers, so fish eggs fail to develop and fish populations fall.
4. It acidifies the soil, which dissolves aluminium ions out of the rock; these are toxic to roots and damage fish gills when washed into waterways.
5. It also leaches away mineral ions such as magnesium and calcium, so trees are deprived of nutrients and their leaves are damaged.

Statement 4.12 — how carbon monoxide harms a person, the chain to write

1. Carbon monoxide is produced by incomplete combustion, when a fuel burns in an insufficient supply of oxygen.
2. It is colourless and odourless, so it cannot be detected by the person breathing it.
3. It diffuses into the blood and binds to haemoglobin in the place oxygen would occupy.
4. It binds far more strongly than oxygen and is not readily released, so that haemoglobin can no longer carry oxygen.
5. Less oxygen reaches the tissues, so cells cannot respire aerobically at the rate needed — causing headache, dizziness, unconsciousness and, at high concentrations, death.

Statements 4.13 and 4.14 — the five greenhouse gases and the human sources of each

Carbon dioxide

Burning fossil fuels in power stations, vehicles and industry; deforestation, which releases carbon and removes the photosynthesis that absorbed it. Dominant because of the quantity released and because it persists for centuries.

Methane

Cattle and other livestock during digestion; rice paddy fields; decaying waste in landfill. Traps far more heat per molecule than carbon dioxide but is released in smaller amounts and breaks down within decades.

Nitrous oxide

Nitrogen fertilisers used on farmland, and vehicle exhausts.

CFCs

Aerosols, refrigerants and older manufacturing processes, now largely banned by international agreement.

Water vapour

The most abundant greenhouse gas, largely outside direct human control; its concentration rises as the atmosphere warms, amplifying the warming caused by the others.

The greenhouse effect itself — the sequence, and the point most answers miss

• Short-wavelength radiation from the Sun passes through the atmosphere and warms the Earth's surface
• The warmed Earth emits longer-wavelength radiation back outwards
• Greenhouse gases ABSORB that longer-wavelength radiation and re-radiate some of it back towards the surface
• Less energy therefore escapes to space, and the surface is warmer than it would otherwise be
• The effect is NATURAL and NECESSARY — without it the mean surface temperature would be about −18 °C. The problem is the ENHANCED effect caused by rising concentrations

Two things that are constantly confused

A. THE GREENHOUSE EFFECT is natural and keeps the Earth habitable. Its ENHANCEMENT by rising gas concentrations is what causes global warming.

B. CFCs damaging the OZONE LAYER is a separate problem with a separate mechanism — that is about ultraviolet radiation reaching the surface, not about trapping heat.

Not this: Carbon dioxide is the worst greenhouse gas because each molecule traps the most heat.

This: Methane traps far more heat per molecule. Carbon dioxide dominates because it is released in vastly greater quantities and persists in the atmosphere for centuries.

Model answer [4 marks]

Explain how sulfur dioxide released from a power station can reduce fish populations in a lake many miles away. [4]

Sulfur dioxide is released when fossil fuels containing sulfur are burned, and it is carried by the wind before dissolving in water droplets in the air, where it is oxidised to form acid rain. When this rain falls into a lake it lowers the pH of the water. Fish eggs fail to develop in acidic water and adult fish are killed, so the population falls. Acid rain also releases aluminium ions from the soil and rock, which are washed into the lake and damage the gills of fish.

Model answer [4 marks]

Explain why breathing carbon monoxide reduces the amount of oxygen reaching a person's tissues. [4]

Carbon monoxide diffuses from the lungs into the blood and binds to the haemoglobin in red blood cells, occupying the site that oxygen would bind to. It binds far more strongly than oxygen and is not readily released, so that haemoglobin can no longer transport oxygen. The blood therefore carries less oxygen than normal. Less oxygen reaches the tissues, so the cells cannot carry out aerobic respiration at the rate they require.

Model answer [3 marks]

Describe how human activities have increased the concentration of methane in the atmosphere. [3]

Cattle and other livestock produce methane during digestion, and the number kept for food has risen greatly. Rice is grown in flooded paddy fields, where methane is produced in the waterlogged soil, and the area under rice has increased. Waste decaying in landfill sites also releases methane.

Mark-losing trap. Sulfur dioxide and carbon monoxide are POISONS. Greenhouse gases work by trapping heat and are not poisonous at these levels.

Mark-losing trap. Carbon monoxide binds to HAEMOGLOBIN in place of oxygen. Say the molecule, not 'it stops you breathing'.

Mark-losing trap. The greenhouse effect is natural and necessary. It is the ENHANCED effect that causes global warming.

Mark-losing trap. CFCs and the ozone layer are a DIFFERENT problem from the greenhouse effect. Do not merge them.

Mark-losing trap. Acid rain damages trees through the SOIL as well as directly — aluminium released, and magnesium and calcium leached away.

3 · Prove it — the five questions

The five questions climb Grade 6 → Grade 7 → Grade 8 → Grade 9 → Grade 9 challenge, and are marked inside Incandio on your own device, by rule, with an authored diagnosis of the mistake you actually made. The mark schemes stay in the app so that the practice is worth doing; the questions themselves are here.

1. Grade 6 · Identify [1 mark] — Which gas is released when fossil fuels containing sulfur impurities are burned, and causes acid rain?
2. Grade 7 · Explain [2 marks] — Explain why a person can be poisoned by carbon monoxide from a faulty boiler without noticing anything is wrong.
3. Grade 8 · Explain [5 marks] — A forest downwind of an industrial region shows dying trees and its lake contains almost no fish. Explain how sulfur dioxide released miles away could cause both. Select every statement that belongs in a full-mark explanation.
4. Grade 9 · Calculate [4 marks] — A country releases 4.2 × 10⁸ tonnes of carbon dioxide and 1.4 × 10⁷ tonnes of methane in a year. Methane traps 25 times as much heat per tonne as carbon dioxide. Calculate the total warming effect of these emissions, expressed as tonnes of carbon dioxide equivalent.
5. 9+ · Analyse [5 marks] — A student writes: 'Carbon dioxide is a pollutant just like carbon monoxide, so the solution to both is the same — filter it out of exhaust gases before they leave the chimney.' Select every statement that belongs in a full-mark evaluation.

The people behind this science

Two ways into the same idea — the one who established that pollution has biological consequences, and the one who knew the cost of an industrial process first-hand. Inside Incandio each of them answers knowing exactly which lesson you have just finished.

Rachel Carson — the one who established that pollution has biological consequences

This page asks you to trace a substance released in one place to damage in another, which is exactly the argument Carson had to construct and then defend. Silent Spring assembled evidence from hundreds of separate studies to show that pesticides were reaching organisms that were never the target, and the chemical industry attacked both the science and her personally. The difficulty she faced is the one this page presents in miniature: harm at a distance is real but hard to prove, because the cause and the effect are separated by miles and by years.

• “How do you prove that harm in one place was caused by something released elsewhere?”
• “What made your evidence strong enough to survive the attacks on it?”
• “Why is pollution that travels so much harder to control?”
• “What should be established before a substance is released widely?”

Marie Curie — the one who knew the cost of an industrial process first-hand

Every gas on this page comes from an industrial or agricultural process, and Curie is one of the few figures who did that work with her own hands. To isolate a tenth of a gram of radium chloride she processed tonnes of pitchblende residue in a leaking shed, stirring boiling vats with an iron rod nearly as tall as herself, breathing whatever came off them. She understood better than almost anyone that obtaining something useful means releasing something else, and she paid for it with her life.

• “What was it actually like to process tonnes of ore by hand?”
• “What came off those vats, and did you think about it?”
• “Is there always a cost to extracting something useful?”
• “Should a process be used before its effects are understood?”

Carry on through the course

• Previous lesson: The Carbon and Nitrogen Cycles
• Next lesson: Global Warming and Deforestation
• Populations, Ecosystems and Sampling with Quadrats — Four nested words for where organisms live — and how to count a population you could never count in full.
• Biodiversity, Distribution and Limiting Factors — Why organisms are where they are and not somewhere else — and how to measure the variety of life in a place rather than just its quantity.
• Food Chains, Webs and Pyramids — Who eats whom, drawn three different ways — and why only one of the three can come out upside down.
• Energy Transfer Along a Food Chain — About nine tenths of the energy disappears at every step. Here is exactly where it goes — and what that means for how the world is fed.
• The Carbon and Nitrogen Cycles — The same atoms, used again and again — and the four bacteria that do the work nothing else can.
• All of Biology · Biology key terms · required practicals · Incandio Science · The 4BI1 specification