The TTZ is an area of about 10,400 sq kms spread over Agra, Firozabad, Mathura, Hathras and Etah in Uttar Pradesh and Bharatpur in Rajasthan.
"There is sudden flurry of activities in TTZ. Is there any particular reason for that? Leather industries and hotels are coming up there. Why?" Justices M B Lokur and Deepak Gupta asked Additional Solicitor General of India, Tushar Mehta, who is representing the state.
The top Court had earlier said that "ad hoc" measures were not enough to preserve the Taj Mahal for "a few hundred years" asked the Uttar Pradesh government to prepare a comprehensive design for the protection of the 17th century mausoleum for generations.
The Taj, said to be one of the seven wonders of the world, has been battling too many challenges with pollution being the most devastating. Observers have noticed a yellow-brown layer on the white marble. A team of researchers from India and the US in 2014 found that the browning was mainly due to dust and airborne carbon particles.
Mudpacks are being applied in stages to erase stains but critics say the process is as damaging as bleaching the fine stone. Authorities have, however, rejected the concern.
The Archeological Society of India (ASI), which is in charge of conservation of the monument, has undertaken many projects to clean up the marble. But critics warn that restoration is only half the solution, pointing to the industrial factories across the river that belch out noxious fumes, leaving the air thick with smog.
Efforts to curb these pollutants, including banning motor vehicles within 500 metres of the building, have also failed to clear up the air.
"We have to clean the dome, but the challenge is how to erect the scaffolding," Bhuvan Vikrama, the government archaeologist overseeing restoration efforts, told AFP.
Among other efforts to ease pressure on the monument, the number of local tourists is being capped to 40,000 a day. Right now, an average of 10,000-15,000 visitors come here every day and the number swells to about 70,000 on weekends.
Meanwhile, the state government has filed a separate application asking for permission to cut 234 trees to lay pipelines for water supply in Agra.
The bench, however, asked the state how many trees have already been planted in the TTZ and posted the matter for hearing after four weeks.
The Taj Mahal, built by Mughal emperor Shah Jahan in the memory of his wife Mumtaz Mahal in 1631, is a UNESCO World Heritage Site.
(With inputs from agencies)
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