New Delhi: The historic Red Fort is experiencing ongoing and increasing damage as a result of the deteriorating air quality in Delhi, according to a recent study. Pollutants are forming black crusts on the red sandstone walls of the 17th-century monument, threatening both its structural stability and aesthetic appeal. This Indo-Italian 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 detailed scientific exploration of the effects of urban air pollution on this landmark, constructed by Emperor Shahjahan between 1639 and 1648.
The research, a collaboration between India’s Department of Science and Technology and Italy’s Ministry of Foreign Affairs (MAECI), involved scientists from IIT Roorkee, IIT Kanpur, Ca’ Foscari University of Venice, and the Archaeological Survey of India (ASI). They analyzed sandstone and black crust samples from various locations within the Red Fort complex, including Zafar Mahal. The results showed that black crusts ranged from thin deposits of about 0.05 millimeters in sheltered areas to thick layers reaching up to 0.5 millimeters on walls exposed to heavy traffic. These thicker layers are firmly attached to the stone surface, risking flaking and damage to intricate carvings.
The researchers found that the black crusts are primarily made up of gypsum, bassanite, weddellite, and small amounts of heavy metals such as lead, zinc, chromium, and copper. These harmful substances are not naturally part of the sandstone but are deposited from external sources like vehicle emissions, cement plants, and construction activities in the area. The study noted that chemical reactions involving pollutants such as sulfur dioxide and nitrogen oxides contribute to the creation of gypsum layers, which are eroded by rain. Additionally, nitrates and oxalates were discovered to penetrate the sandstone, inducing internal stress, cracks, and biological growth.
The team also reported blistering, salt crystallization, and deterioration linked to moisture near entrances, while the interior Makrana marble decorations exhibited relatively less damage due to their denser grain structure. By analyzing air quality data from the Central Pollution Control Board spanning 2021 to 2023, the researchers confirmed that fine particulate matter levels were over two and a half times higher than national limits, with coarser particles exceeding the threshold by more than three times.