Some types of lichens only grow in places where there is little or no contamination. By simply observing what types of lichen grow in an area scientists can determine the level of contamination and the air quality of an area.

Lichens do not grow in places where there are high levels of contamination. Only onw or two types of lichen grow in places where there are medium levels of contamination. A large variety of lichens grow in places where there are low levels of contamination.