Why is it advised that industries should switch over to cleaner fuels such as CNG and LPG in the Taj Mahal zone in Agra?

Industries should switch over to cleaner fuels such as CNG and LPG in the Taj Mahal Zone in Agra because by using fossil fuels they release sulphur dioxide and nitogen dioxide gas into the atmosphere which causes acid rain.

Acid rain reacts with the carbonates present in marble (calcium carbonate) and limestone of a monument and corrodes it slowly (dissolve it slowly).