Pollution leaves two different marks on the marble
The Taj Mahal’s discoloration is not caused by one stain spreading across the monument. Airborne dust and pollution particles settle on its white marble, dulling its surface and contributing to a yellow cast. Pollutants can also react with moisture and the stone, making the damage more than a layer of dirt that rain can simply wash away.
The river can affect the walls, too
Green patches have a different suspected source: tiny insects that breed around the Yamuna River, beside the monument. Their droppings can land on the marble and leave greenish marks. The river’s degraded water quality is part of this local environmental problem, though the green staining is not simply algae growing on the building.
These processes show how the Taj’s setting connects its appearance to both the air over Agra and the condition of the nearby river. Cleaning can restore the marble’s brightness for a time, but fresh deposits keep returning as long as the sources of pollution remain. The discoloration is a visible record of environmental pressures acting on the monument’s surface.
