Which pollutant causes Taj Mahal discoloration?
Sulfur dioxide from refineries, combustion, and other sources around Agra contributes to marble deterioration and discoloration. Atmospheric oxidation produces sulfuric acid and sulfate; these react with calcium carbonate in marble to form gypsum, which is more soluble and traps soot and dust, creating a yellowed or darkened surface. Nitrogen oxides and particulates may contribute, so attributing all damage exclusively to one pollutant is a simplification. Atmospheric inversions can trap contaminants near the surface, while wind, turbulence, precipitation, and chemical transformation determine
Ref: Campbell Biology, Urry et al., 12th Ed., Unit 8 Ecology