Although the Taj Mahal may appear to the untrained eye almost as perfect as the day it was completed, the marble is undeniably sullen and yellow in parts, and empty casings here and there betray lost precious stones. These are the early effects of the threat posed by pollution from traffic and industry, and the millions of tourists who visit the tomb year-round. While marble is all but impervious to the onslaught of wind and rain that erodes softer sandstone, it has no natural defence against the sulphur dioxide that lingers in a dusty haze and shrouds the monument; sometimes the smog is so dense that the tomb cannot be seen from the fort. Sulphur dioxide mixes with atmospheric moisture and settles as sulphuric acid on the surface of the tomb, making the smooth white marble yellow and flaky, and forming a subtle fungus that experts have named "marble cancer" .

 

The main sources of pollution are the 1700 factories in and around Agra, and the continuous flow of vehicles along the national highways that skirt the city. Chemical effluents belched out of factory chimneys are well beyond safety limits laid down by environmental committees. Despite laws demanding the installation of pollution-control devices, the imposition of a ban on all petrol- and diesel-fuelled traffic within 200m of the Taj Mahal, and an exclusion zone marking 10,400 square kilometres around the complex that should be free of any new industrial plants, pollutants in the atmosphere have continued to rise, and new factories have been set up illegally. In 1993, the Supreme Court finally took action and ordered nearly three hundred plants to shut down until emissions fell to legal limits.

Cleaning work on the Taj Mahal rectifies the problem to some extent, but the chemicals used will themselves eventually affect the marble. Already attendants shine their torches on repaired sections of marble to demonstrate that they have lost their translucency. The doubtful methods of the Archaeological Survey of India, such as scrubbing with toothbrushes, may prove disastrous in the long term. Hopes for proper care of the Taj Mahal have been raised since the government turned its attention to the plight of India's greatest monument, and entry fees for foreign visitors have been increased substantially, amid great controversy, to regulate the flow of tourists and generate much needed income, but the fate of the Taj Mahal hangs in the balance.

For more on the admission fee controversy, see Viewing Practicalities