As threat to the Taj Mahal due to harmful gases emanating from nearby industries continue, green activists are now emphasising the need for implementation of a 'clean air action plan' to save the Mughal-era structure.

Though environmentalists have been raising a hue and cry time and again, this time they have rung the alarm bell by flagging concerns over emissions from vehicles due to uninterrupted flow of traffic.

Industrial pollution is increasingly "threatening the environmental equilibrium" around the epitome of Mughal heritage, they say and suggest that a cap on the number of visitors should be introduced at the monument.

Currently, 25,000 to 42,000 people visit the monument every day.

"Agra should have a clean air action plan. The traffic in the city is a nightmare. Air pollution, vehicular pollution is very high in the city. Green fuel like CNG should be introduced in Agra," Chandra Bhushan, Deputy Director General of Centre for Science and Environment (CSE), a leading green NGO, said.

He, however, dismissed the argument that the opening up of Yamuna Expressway may be posing a fresh threat to the monument.

"I think, it is a temporary phenomenon," he said.

Former Director General of National Museum, C V Ananda Bose said, "It is common knowledge that any increase in humidity in temperature will affect the environmental balance" and the Archaeological Survey of India, which is responsible for protection of the monument, should take steps to protect the the structure.

"We should not forget that Taj is the symbol of India's pride. We have inherited this monument from our forefathers and we should retain it for our children. If we fail in this, it is a sin against our children," Bose said.