Ozone is a complicated suspect - she is both good and bad. She is a gas which has a blue colour and a funny smell. She occurs naturally, high up in our atmosphere and helps to protect us by removing harmful rays from the sun. But at ground level, she can make breathing difficult. She can also irritate our airways and eyes, as well as damage our lungs.

Most ozone found at ground-level is made in the atmosphere from a reaction with sunlight and other pollutants. Ozone can react with nitric oxide - which is usually found in towns and cities, near to roads. This means that more ozone is usually found in the countryside, away from the busy roads. Levels of ozone are highest on hot, still and sunny days.

Once you've read about all the suspects that cause pollution, take the quiz by clicking below: