C11.5 Atmospheric Pollutants

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Pollution from fuels

• Fossil fuels include coal, oil and natural gas.

• When fuels burn, they can make useful energy and pollutants.

• The products depend on:

- the elements in the fuel

- impurities in the fuel

- the amount of oxygen available

Open with the main chemistry idea: products are not random. They depend on composition and conditions.

Complete combustion

• A hydrocarbon is a substance made of carbon and hydrogen atoms only.

• When any fuel burns in plenty of oxygen (air), it undergoes complete combustion.

Methane as an example

For natural gas, which is mainly methane:

CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g)

methane + oxygen → carbon dioxide + water

Remind students that water is written as gas here because it is formed in the flame at high temperature.

What are the main products of complete combustion of methane?

A

carbon dioxide and water

B

carbon monoxide and water

C

sulfur dioxide and water

D

nitrogen oxides and water

Checks the core idea from slides 2 to 5: with plenty of oxygen, a hydrocarbon forms carbon dioxide and water.

Why is carbon dioxide a problem?

Carbon dioxide is a problem because it is a greenhouse gas. It traps heat in the Earth's atmosphere, causing the planet to warm up.

This can lead to:

• Climate change

• Rising sea levels

• More extreme weather, such as floods, droughts, and heatwaves

• Changes to habitats, affecting plants and animals

Not all fuels are pure

• All fossil fuel contain at least some sulfur.

• Reaction with oxygen

  • Sulphur + oxygen → Sulphur dioxide

  • Sulphur dioxide is an acidic and toxic gas.

Acid rain

• Sulphur dioxide and nitrogen oxides can cause acid rain.

• Acid rain damages trees.

• It kills plants and animals in lakes.

• It also attacks limestone buildings and metal structures.

Link back to everyday examples such as statues, old buildings or damaged woodland.

Which pollutant is made when sulfur in fuel burns?

A

carbon monoxide

B

sulfur dioxide

C

nitrogen oxide

D

water vapour

Targets the impurity idea: sulfur in the fuel leads to sulfur dioxide.

Incomplete combustion

When a fuel burns in a limited supply of oxygen, it undergoes incomplete combustion.

• The fuel does not fully oxidise.

• Incomplete combustion may also produce unburnt hydrocarbons and carbon particles.

Stress the link between oxygen supply and products formed. This is a key predictive idea.

Carbon monoxide forms

For methane in limited oxygen:

Methane + limited oxygen → Carbon monoxide + water

This shows incomplete combustion.

Students may expect CO2 every time. Point out that the oxygen supply changes the carbon product.

Why carbon monoxide is dangerous

• Carbon monoxide is toxic.

• It is colourless and odourless.

• People cannot easily tell they are breathing it in.

Effects of carbon monoxide poisoning

Carbon monoxide binds to haemoglobin → less oxygen carried in blood → body cells become starved of oxygen → the person becomes drowsy, may lose consciousness, and can die.

Use the arrow chain because the causal sequence is the whole teaching point here.

What condition causes incomplete combustion?

A

too much sulfur

B

limited oxygen

C

low carbon fuel

D

extra nitrogen

A key predictive rule from slides 11 to 15.

Complete the gap

If there is not enough oxygen, combustion is incomplete. This can produce carbon monoxide, which is poisonous. It binds to haemoglobin so less oxygen is carried around the body.

oxygen

carbon monoxide

haemoglobin

carbon dioxide

sulfur dioxide

plasma

nitrogen

Good for linking the condition, pollutant and danger in one short text.

Nitrogen oxides

• Car engines become very hot when they are running.

  At these high temperatures, nitrogen and oxygen from the air react together to form nitrogen oxides (NOₓ).

• This is a toxic gas.

Students often think nitrogen oxides come from nitrogen in fuel. Emphasise they form from nitrogen in the air.

Problems caused by nitrogen oxides

• Nitrogen oxides can trigger some people's asthma.

• They cause breathing problems.

• Like sulfur dioxide, they also contribute to acid rain.

• Nitrogen dioxide can help give smog a brown colour.

Where do nitrogen oxides in car engines mainly come from?

A

nitrogen in diesel

B

nitrogen in the air

C

carbon in fuel

D

sulfur in oil

Addresses the common misconception flagged in the teacher note on slide 16.

Particulates

• Diesel engines burn hydrocarbons with bigger molecules than petrol engines.

• Tiny solid particles containing carbon and unburnt hydrocarbons are produced.

• These particles are called particulates.

Problems caused by particulates

• Particulates are carried into the air.

• They can travel into the upper atmosphere.

• They reflect sunlight back into space.

• This can cause global dimming.

Particulates and health

• Scientists think particulates may damage cells in the lungs.

• They may increase the risk of cancer.

• So particulates are both an environmental and a health problem.

Which pollutant is most linked to global dimming?

1

particulates

2

carbon monoxide

3

sulfur dioxide

4

water vapour

Complete or incomplete?

Complete combustion

• plenty of oxygen

• mainly carbon dioxide + water

Incomplete combustion

• limited oxygen

• carbon monoxide, particulates, and unburnt hydrocarbons may form

How conditions change products

Fuel composition + burning conditions decide the products:

• carbon in fuel → carbon dioxide

• hydrogen in fuel → water

• sulfur impurity → sulfur dioxide

• limited oxygen → carbon monoxide

• high engine temperature → nitrogen oxides

• incomplete burning of large molecules → particulates

This is the key summary logic of the lesson and links directly to the learning objective.

Pollutant and problem

Main problem

Greenhouse effect and climate change

Acid rain; toxic gas

Poisonous; stops blood carrying enough oxygen

Breathing problems; acid rain

Global dimming; lung damage

Carbon dioxide

Sulfur dioxide

Carbon monoxide

Nitrogen oxides

Particulates

Pollutant

Useful consolidation slide before the glossary.

Vehicles and real emissions

• Motor vehicles are a major source of air pollution.

• Modern engines are improving to meet legal limits.

• Real driving can produce higher levels of pollutants such as nitrogen oxides.

This provides contemporary context from the source material without drifting away from chemistry.

Power stations and pollution

• Old coal-fired power stations can release large amounts of pollutants.

• Acid rain and tiny acidic particles can be carried long distances.

• Pollution can be deposited on land and in waterways far away.

Which pair best predicts pollutants from burning fuel?

A

colour and smell

B

mass and volume

C

fuel and conditions

D

speed and cost

Checks the central model from slides 22 to 27.

Complete the gap

To predict atmospheric pollutants, ask what is in the fuel and how it is being burnt. Limited oxygen can form carbon monoxide, while high engine temperature can form nitrogen oxides.

fuel

burnt

carbon monoxide

water

cooled

sulfur dioxide

air

A compact summary task using the final key idea slide.

How are complete and incomplete combustion different?

Accept answers that compare complete combustion with incomplete combustion using oxygen supply and products.

One thing you will remember from this lesson

Use as a quick plenary mind-map starter. Invite students to explain one frequent word from the cloud.

What helped you understand this topic best?

Reflection only. Encourage students to mention a slide, example, equation, gap-fill, discussion or summary table that supported them.

Which part of this lesson felt hardest?

Reflection only. Useful for planning retrieval or reteaching next lesson.

Glossary

combustion - a reaction in which a substance burns in oxygen

complete combustion - burning in plenty of oxygen to form carbon dioxide and water

incomplete combustion - burning in limited oxygen, which can form carbon monoxide and particulates

hydrocarbon - a compound made only of hydrogen and carbon

impurity - an unwanted substance mixed with a fuel

pollutant - a substance that causes harm in the environment

flue gas - waste gas released from a power station or furnace

Glossary

sulfur dioxide - an acidic, toxic gas made when sulfur impurities burn

carbon monoxide - a poisonous gas formed by incomplete combustion

nitrogen oxides - toxic gases formed when nitrogen and oxygen react at high temperatures

particulates - tiny solid particles, often carbon and unburnt hydrocarbons

acid rain - rain made acidic by pollutants such as sulfur dioxide and nitrogen oxides

greenhouse gas - a gas that absorbs energy leaving Earth

global dimming - reduced sunlight reaching Earth because particles reflect sunlight back into space