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Cars and the Environment

A petrol or diesel car burns fuel and sends gases out of the tail pipe. Some gases are harmful: carbon monoxide, nitrogen oxides, unburnt fuel and soot. Carbon dioxide traps heat. A catalytic converter turns the worst gases into less harmful ones. Lighter cars, smaller engines, hybrids and electric cars use less fuel or none at all, so the air stays cleaner. Good maintenance and smooth driving also cut pollution.

🎬 Step-by-step story

  1. This car burns fuel. See the dark puffs? That is exhaust, gas leaving the tail pipe.
  2. Now there are two cars. Twice the cars means twice the puffs. Many cars in a city make the air dirty.
  3. A catalytic converter (orange box) is added. Look: the puffs turn green after it. The worst gases become less harmful.
  4. A lighter car needs less fuel. Burning less fuel means fewer puffs. Slow, smooth driving does the same.
  5. An electric car has no exhaust pipe, so no puffs come out of it. Its power station may still make some pollution.
  6. Your turn. Change the number of cars and switch the converter on or off. Watch the counts change.

Tip: drag the 3D scene to turn it. Use two fingers to zoom.

🤔 Common doubts, cleared

Why do the puffs go away in an electric car?

There is no fuel burning inside the car, so there is nothing to push out of a pipe.

Does a converter make carbon dioxide too?

Yes. It changes CO into CO₂. CO₂ is far less poisonous but still warms the air, so using less fuel matters.

Why does a lighter car pollute less?

It needs less push to move, so the engine burns less fuel and sends out fewer gases.

Do more cars really make worse air?

Yes. Every car adds its own puffs, so the total grows with the number of cars.

Why cars can harm the air

Petrol and diesel are fuels made of carbon and hydrogen. When the engine burns them, it needs air. If burning were perfect, we would only get carbon dioxide and water. But burning in an engine is never perfect.

Cleaning the exhaust

A catalytic converter sits in the exhaust pipe. Inside is a honeycomb coated with rare metals (like platinum). These metals act as a helper (a catalyst) and are not used up. They change gases:

Diesel cars also use a particle filter to catch soot. A converter works only when it is hot, and leaded petrol would spoil it. Regular engine tuning and a pollution check make sure the converter and engine still work well.

Using less fuel

Less fuel burnt means less gas out. Ways to save fuel:

Fuel economy tells how far a car goes on one litre (km/L), or how many litres it needs for 100 km (L/100 km).

Hybrid and electric cars

A hybrid car has a small engine and an electric motor with a battery. At slow speed it uses the motor, so it burns less fuel. An electric car (EV) has only a battery and a motor. It has no tail pipe, so no exhaust in the street. It is also quiet. Its power still comes from a power station, so it is cleanest when the electricity is made from sun, wind or water. Old batteries must be recycled, not thrown away.

Try it: count the puffs

Open the 3D. Predict first: with 2 cars and the converter ON, will there be more green puffs or more dark puffs? Switch it on and check. Then at home, ask an adult whether your family car has a valid pollution check certificate, and note when it is due.

Key formulas and definitions

Worked examples

1. A car goes 180 km on 12 litres. What is its fuel economy?

Fuel economy = 180 ÷ 12 = 15 km/L.

2. How much fuel does the same car need for a 300 km trip?

Fuel = 300 ÷ 15 = 20 litres.

3. Using 2.3 kg of CO₂ per litre, how much CO₂ do 20 litres of petrol give?

20 × 2.3 = 46 kg of CO₂.

4. Car A gives 10 km/L and car B gives 20 km/L. How much petrol does each use for 400 km?

A: 400 ÷ 10 = 40 L. B: 400 ÷ 20 = 20 L. B uses half, so it makes half the CO₂.

5. A converter changes poisonous CO. Write what it becomes.

It becomes carbon dioxide (CO₂), which is not poisonous.

Common mistakes

Practice quiz

1. Which gas from a car is poisonous and has no smell?
2. What does a catalytic converter do?
3. Which car has no tail pipe exhaust?
4. A car goes 100 km on 5 L. Fuel economy is:
5. Which habit saves fuel?

Practice: answer these yourself

Type or choose your answer, then press Check. Use a hint if you are stuck; the full solution appears after you answer.

Frequently asked questions

How do cars pollute the air?

The engine burns fuel and the exhaust carries out gases like carbon monoxide, nitrogen oxides, unburnt fuel, soot and carbon dioxide.

What is a catalytic converter in simple words?

It is a box in the exhaust pipe with special metals inside. They change harmful gases into safer ones without being used up.

Are electric cars really better for the environment?

Yes in most cases. They give no tail pipe gas and are more efficient. They are best when the electricity is made from clean sources and when old batteries are recycled.

Where this is taught

Japan高校（専門学科）1〜3年Automotive Engineering

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