new delhi: The iconic Red Fort is facing gradual and accelerating damage due to Delhi’s deteriorating air quality, a recent study has found.
Black crusts of pollutants are steadily forming on the red sandstone walls of the 17th-century monument, threatening its structural and aesthetic integrity, according to a new Indo-Italian study.
The study, titled “Characterisation of red sandstone and black crust to analyse air pollution impacts on a cultural heritage building: Red Fort, Delhi, India”, is the first comprehensive scientific investigation into how urban air pollution is impacting the historic monument built by Emperor Shahjahan between 1639 and 1648.
Developed as part of a collaboration between India’s Department of Science and Technology and Italy’s Ministry of Foreign Affairs (MAECI), the research was conducted by scientists from IIT Roorkee, IIT Kanpur, Ca’ Foscari University of Venice, and the Archaeological Survey of
India (ASI) this year.
The team analysed samples of sandstone and black crust collected from different areas of the Red Fort complex, including Zafar Mahal.
The findings revealed that black crusts varied from thin deposits of approximately 0.05 millimetres in sheltered areas to thick layers of up to 0.5 millimetres on walls facing high-traffic zones.
These thick layers are strongly bonded to the stone surface, posing a risk of surface flaking and loss of intricate carvings.
According to the researchers, the black crusts primarily consist of gypsum, bassanite, weddellite, and trace amounts of heavy metals such as lead, zinc, chromium, and copper. These pollutants are not inherent to the sandstone but are deposited from external sources, including vehicular emissions, cement factories, and construction activities in the city.
The study highlighted how chemical reactions between pollutants like sulphur dioxide and nitrogen oxides lead to the formation of gypsum layers, which eventually erode during rainfall.
Moreover, nitrates and oxalates were found to infiltrate the sandstone, causing internal stress, cracks, and biological growth. The team also observed blistering, salt crystallisation, and dampness-related crumbling near entrances, while interior Makrana marble decorations showed comparatively less damage due to their stronger grain structure.
Accessing air quality data from the Central Pollution Control Board for the years 2021 to 2023, the researchers confirmed that fine particulate matter concentrations remained more than two and a half times above national limits, with coarser particles exceeding the threshold by over three times.
Nitrogen dioxide levels also crossed safe limits, contributing to the stone’s gradual decay, even though ammonia and sulphur dioxide levels were within limits.
“This is a wake-up call. Regular cleaning, protective coatings, and stricter pollution control measures are essential if the Red Fort and other heritage sites are to be preserved for future generations,” the study concluded.
The Red Fort, built between 1639 and 1648 and a UNESCO World Heritage site since 2007, spans one square kilometre with massive red sandstone walls. Originally protected by a moat and the Yamuna, it now faces heavy pollution.