Not Just Lungs, Red Fort Turning Black In Delhi’s Toxic Air

Last Updated:September 16, 2025, 21:57 IST

As per a study, black crusts of pollutants are forming on the red sandstone walls of the Red Fort

The study termed this a “wake-up” call, and Red Fort and other heritage sites should be cleaned regularly. (Photo: PTI file)

The severe air pollution in Delhi is not just choking the lungs of residents but has now started to damage the iconic structures that symbolise the capital.

As per a study, black crusts of pollutants are forming on the red sandstone walls of the Red Fort, a place from where the Prime Minister of India delivers the Independence Day address every year.

Samples of sandstone and black crust were collected from different areas of the Mughal-era complex, including Zafar Mahal.

The study, titled “Characterisation of red sandstone and black crust to analyse air pollution impacts on a cultural heritage building: Red Fort, Delhi, India”, found 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.

The research was conducted by scientists from IIT Roorkee, IIT Kanpur, Ca’ Foscari University of Venice, and the Archaeological Survey of India (ASI) as part of a collaboration between India’s Department of Science and Technology and Italy’s Ministry of Foreign Affairs (MAECI).

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.

The study termed this a “wake-up” call, and Red Fort and other heritage sites should be cleaned regularly. It asked authorities to undertake stricter pollution control measures to protect these sites.

Red Fort

Mughal emperor Shah Jahan started the construction of the Red Fort in 1639 after he shifted his capital from Agra to Shahjahanabad, now known as Old Delhi. Opened in 1648, the structure was built mainly of red sandstone using Persian, Timurid, and Indian architectural styles. In 2007, it was inscribed on the UNESCO World Heritage list.

(with inputs from PTI)

About the Author

Saurabh Verma

Saurabh Verma covers general, national and international day-to-day news for News18.com as a Senior Sub-editor. He keenly observes politics. You can follow him on Twitter –twitter.com/saurabhkverma19

Saurabh Verma covers general, national and international day-to-day news for News18.com as a Senior Sub-editor. He keenly observes politics. You can follow him on Twitter –twitter.com/saurabhkverma19

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