What explains the absence of lichens in parks and forests located near large industrial centers?

In fact, there will be a lot more lichens in industrial areas, near roads and in polluted areas. Lichens do not grow in ecologically clean areas. Moreover, they serve as a kind of indicators. Where the air is polluted, there are many lichens on trees and rocks. If the factories threw out especially hazardous chemical waste, then the trees would be the first to suffer, and only then the lichens. Since they have a low growth rate and defense mechanisms. Research has shown that lichens can survive for two weeks without an atmosphere.