Taj Mahal is one of the strongest monument and is made up of white marble. It is damaged due to acid rain. This phenomenon is called:
Marble cancer
Oxides of Nitrogen and Sulphur form acids when reacted with water vapour present in the atmosphere. Nitrogen dioxide forms Nitric acid whereas Sulphur dioxide forms Sulphuric acid on reaction with water vapour. This results in acid rain. Acid rain corrodes white marble of Taj Mahal. This phenomenon is called Marble cancer.