EVERYDAY SCIENCE

Detailed explanation-1: -Sulfur dioxide causes acid rain that can kill plants and aquatic animals [4, 13]. For example if there are no lichens present, the air quality is very poor (lichen desert, critical area of contamination), whilst generally only crusty lichens can tolerate poor air quality (zone of strong pollution).

Detailed explanation-2: -Lichens do not have roots; instead they receive all their nutrients from the atmosphere. Lichens are sensitive to atmospheric pollution such as nitrogen (N) because they receive all their nutrients and water from wet and dry atmospheric deposition (fall out).

Detailed explanation-3: -As a rule of thumb, the smaller the size and less variety of lichens in an area, the more polluted is the environment. Two main air pollutants that affect lichen growth are nitrogen and sulphur dioxide.

Detailed explanation-4: -The algae in lichens photosynthesize (create food from sunlight energy), and both the algae and fungus absorb water, minerals, and pollutants from the air, through rain and dust. Some sensitive lichen species develop structural changes in response to air pollution including reduced photosynthesis and bleaching.

Detailed explanation-5: -Sulfur dioxide, is a pollutant which when mixed with rainwater or air can damage lichens and does not allow them to grow due to which they act as natural indicators of air pollution. Therefore the absence of lichens indicates that the area is heavily polluted with sulfur dioxide.