They may have stood the test of time, but Delhi’s monuments could now be affected by the city’s highly polluted air.

While some experts believe that a spurt in air pollution levels may cause historical structures to erode, others say it may take another century for the monuments to get corroded. With several monitoring stations across Delhi reporting “severe” pollution warnings, the poor air quality has caught the attention of conservationists.

A retired Archaeological Survey of India official said that vehicular emissions in Delhi would have long-term impact on the monuments. “But more alarming would be if we had acid rain, as sulphur dioxide has a dissolution effect on marble,” said the official.

The combined assault of air pollution and acid rain would be more pronounced on monuments with a white façade, according to AGK Menon, the convenor of INTACH’s Delhi chapter.

“Structural damage to the Taj Mahal’s white surface is more visible, unlike the damage done to the surface of Humayun’s Tomb or the Parliament,” he said.

However, a section of experts say that Delhi’s monuments, which are mostly built with long-lasting materials, cannot be eroded just by air pollution alone.

“It is the limestone structures of Europe that are susceptible to damage from air pollution. In Delhi, the monuments, including Humayun's Tomb, are built to last,” said Ratish Nanda, a conservation architect and the projects director for the Aga Khan Trust for Culture.

He added that the particulate matter that harms humans the most can easily be washed off buildings, which is something the management of the Lotus Temple does.

The National Green Tribunal is currently hearing a petition filed by lawyer Sanjeev Ailawadi, who had said that vehicular emissions were turning the white marble façade of the Lotus Templte yellow. Arguments are on in the case.

Meanwhile, there is a growing demand for the need to protect monuments. The NGO Itihaas organised its seventh annual summit on Tuesday to focus on preserving cities’ heritages. The speakers addressed about 125 educationists on the need to get students involved with conserving heritage.