Question: Why is the brightness of historical monuments made of marble stone like the Taj Mahal gradually decreasing? What is the possible remedy?
Causes of the discolouration of the Taj Mahal
SO2 gas emitted from acid factories located around the Taj Mahal and also SO2 emitted from the Mathura oil refinery oxidizes in the atmosphere to SO3 and mixes with water vapour or rainwater to produce H2SO4. This acid forms a coating of CaSO4 on the marble Taj Mahal. As a result, the brightness of the Taj Mahal is gradually decreasing.
CaCO3 + H2SO4 = CaSO4 ↓ + CO2 ↑ + H2O
How to protect the Taj Mahal from dimming?
To protect historical monuments like the Taj Mahal, there should be a ban on setting up factories around them. Industries like oil refineries should be built outside 100 km. Excessive vehicular movement in the vicinity of monuments should be controlled. Only then all these monuments can be saved.