"Damage to the Ashoka Pillar is a serious matter and our team of experts is exploring various reasons which may have led to the erosion," said V K Saxena, director, ASI's Science division, in Lucknow on Sunday for an official meeting. He added, "Though it is difficult to say anything concrete right now, we are looking at different causes, including air pollution."

Level of air pollution in Delhi is among the highest in the world and Supreme Courthas expressed concern over the matter. The impact of air pollution on health and environment is much discussed, while its effect on monuments is still coming up for discussion. If it is proved that air pollution caused the layer bearing text on the Ashoka Pillar, environment activists may get another big reason to battle pollution.

Saxena said he believed in the scientific principle that everything happening is some kind of a chemical reaction. "As of now, a cumulative effect caused by the rock's composition, environmental factors like microbial growth and chemical reactions in air are among factors that may have caused erosion. But anything concrete can be said once the experts present their report," he stated.

There is no dearth of material suggesting how air pollution puts cultural heritage at risk. According to a study shared by United Nations Economic Commission for Europe (UNECE), "Air pollution is a key factor in degrading of surfaces of historical buildings and monuments. The impact of pollutants emitted is enormous and often irreversible. Corrosion caused by chemicals and soiling caused by particles can not only lead to economic loss but also damage cultural heritage."

A 2015 study led by the Italian Institute for Environmental Protection and Research (ISPRA) and the Institute for Conservation and Restoration of Heritage (ISCR) noted that in Rome, about 3,600 cultural heritage properties made of limestone and 60 cultural heritage objects made of bronze are at risk of deterioration. The loss of material as a result of air pollution in Rome was estimated between 5.2 and 5.9 microns per year for marble and between 0.30 and 0.35 microns per year for bronze. In response to the threat, Italy has been engaged in development of strategies and technologies to safeguard cultural heritage assets for many years.

'No chemicals used to clean Ashok pillar in 15 yrs'

ASI chief of the science division V K Saxena denied chemical cleaning had led to the erosion of the Ashoka Pillar. "We got our records examined and found no chemical cleaning activity has taken place on the said monument in the past 15 years," he said. Saxena also claimed that chemical cleaning was a globally accepted, scientifically tested and reliable method used for conservation of heritage monuments.

"Experts all over the world have been using for decades the method that ASI uses for monuments including the Taj Mahal across three divisional and 14 zonal offices as and when required," he stated. Explaining that chemical cleaning may involve 3-4 stages, he said, "It is assumed that chemical cleaning is for face-lift of monuments but actually it contributes towards strengthening the monument and preparing it to battle environmental hazards."