Effects of air pollution

In the past, when smoke was the predominant air pollutant, its effects were easy to see. Even today, black incrustations on older buildings in many large cities are still evident. In addition, clothes were soiled, curtains and hangings were blackened and plant growth was affected. City gardeners carefully chose only the most resistant plants. Early last century, the trees around industrial centres became so blackened that light-coloured moths were no longer camouflaged. Melanic (dark) forms became more common because predators could see them less easily. Plants are also very sensitive to SO2 and one of the first effects seems to be the inhibition of photosynthesis.

The traditional smog generated by coal burning contained SO2 and its oxidation product, H2SO4, in addition to smoke. Sulphuric acid is a powerful corrosive agent and rusts iron bars and weathers building stones. Architects sometimes complained of layers of sulphate damage 10 cm thick on calcareous stone through the reaction:

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