We all need the air around us in the atmosphere to breathe and to live. It can be harmful to us if there are high levels of pollution in the air that we are breathing.
Air pollution can irritate our eyes, throat and lungs. People who already have breathing problems - like asthma or heart or lung diseases - are likely to be very sensitive to air pollution. Other people who might be affected by air pollution are the very young or the very old.
If you are sensitive to air pollution you might start to cough or find it difficult or painful to breathe when air pollution is High, especially if you are running around outside or playing sports. In this case it is best to stay indoors if you can. Some people might not notice any effects at all.
But air pollution isn't only harmful to humans. Some pollutants like nitrogen dioxide and sulphur dioxide contribute to acid rain, which can damage crops, forests and materials, or harm animals and fish.