(a) Acid rain is the outcome of air pollution. Air pollution affects inanimate objects like stone and metallic structures, idols concrete, brick walls, paintings etc. Acid rain has caused significant damage to the once snow white marble with which the Tajmahal was built. It is a pity that the beauty of this wonderful monument is being withered away. Acid rain can contaminate surface water and ice and turn soil infertile. It can turn evergreen grassland into desert.
(b) Lichens is a special kind of small plant that grows on rocks, tree trunks and bare soil. They flourish in places where the air is unpolluted. It means that lichens are specially sensitive to air pollution. Therefore, the presence or absence of lichens can indicate the degree of air pollution in a locality.