New Delhi, August 2 - A collaborative study conducted by the Indian Institutes of Technology (IIT) in Roorkee and Kanpur has revealed that air pollution is accelerating the deterioration of the sandstone used in the Humayun's Tomb, a UNESCO World Heritage Site. The findings were published in the 'International Journal of Architectural Heritage'. The research involved analyzing samples of the black layer collected from various sections of the tomb using laboratory techniques to understand their chemical composition, mineral content, and microstructure.

The research team discovered that the black layer primarily consists of gypsum, which forms when sulfur dioxide from polluted air reacts with moisture and calcium-rich dust. According to the study, this gypsum layer traps soot, dust, and fine metal particles emitted from vehicle exhaust, construction activities, road dust, agricultural waste burning, and industrial pollution, gradually creating a black coating on the sandstone. The study indicated that the thickest black layer formed in areas of the monument that were sheltered from rain, where pollutants accumulate over time, while more exposed surfaces had thinner layers due to natural washing away of some pollutants by rain.

Researchers emphasized that the black layer is not merely a surface stain. The chemical reactions that create this layer gradually weaken the sandstone, making it more vulnerable to weathering and long-term damage. They stated that the study scientifically establishes a link between air pollution and the degradation of Humayun's Tomb, which could assist authorities in implementing preservation measures for this historic site.

The study recommends periodically removing the black layer using scientifically validated conservation methods, continuously monitoring pollution around the monument, and assessing protective coatings before application. It also suggests limiting pollution sources through clean transportation systems and low-emission fuels to prevent harmful deposits from forming. The tomb was commissioned in the 16th century by Begum Bega in memory of Mughal Emperor Humayun.