Delhi’s worsening air pollution is not only choking its people but also damaging one of its most iconic landmarks, the Red Fort. A new study has shown that toxic deposits are forming on the 17th-century Mughal monument, putting its heritage value at serious risk.

The research, published in the journal Heritage, shows that black crusts of pollutants are settling on the fort’s red sandstone walls. These crusts, varying in thickness from 0.05 mm to 0.5 mm, were found during a study conducted between 2021 and 2023.

The investigation was carried out by experts from IIT Roorkee, IIT Kanpur, Università Ca’ Foscari of Venice, and the Archaeological Survey of India (ASI).

The crusts were found to contain gypsum, bassanite, weddellite, and harmful heavy metals like lead and zinc. Researchers traced these pollutants to vehicular emissions, cement factories, and construction activities in the capital.

Chemical reactions between the pollutants worsen the problem. During rainfall, the gypsum layers erode, increasing the rate of surface decay.

The study noted that PM2.5 and PM10 particulate matter, tiny dust and smoke particles, are among the main reasons for the fort’s darkened appearance. Over time, these particles settle on exposed surfaces, leading to visible discoloration.

Researchers also observed blistering, salt crystallization, dampness-related crumbling, and structural stress near some entrances of the fort. Harmful compounds like nitrates and oxalates were found penetrating the sandstone, triggering biological growth and further weakening the walls.

Commissioned by Mughal Emperor Shah Jahan in 1639 and completed in 1648, the Red Fort has stood as a symbol of India’s history and culture for centuries. It was declared a UNESCO World Heritage site in 2007.

But the study warns that without urgent intervention, the fort’s structural integrity may suffer. Experts recommend timely conservation strategies, including the use of protective coatings or sealants, especially on areas worst affected by pollution.