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Intense atmospheric contamination in India's capital city of Delhi has caused the appearance of dark layers on the walls of the Mughal-era structure, a new study finds.

Scientists discovered that these crusts—produced due to reactions between pollutants and the sandstone structure—were ranging from 0.05mm and 0.5mm thick, and could harm its detailed artwork if no action implemented.

This investigation is the pioneering of its category to comprehensively examine the effects of polluted air on this 17th Century site.

Heritage advocates have frequently cautioned about the detrimental influence of contamination on cultural sites in the capital and multiple other states.

Previously, courts remarked that the Taj Mahal—similarly iconic historic building—had changed color due to pollutants, prompting immediate conservation steps.

The study on the Red Fort, shared in a scientific publication in June, was carried out from 2021 and 2023 by specialists in multiple countries.

The historical site, constructed by ruler Shah Jahan, is a key India's most prominent cultural landmarks.

India's first leader Nehru hoisted the flag from the monument on August 16 1947, following freedom from British rule was announced. To this day, prime ministers have been giving addresses on August 15 from the ramparts of the monument.

Researchers reviewed Delhi's pollution data from 2021 to 2023. They then sampled the sooty layer detected on multiple surfaces of the fort and tested its content.

They determined that pollutants and other elements in the atmosphere had led to the black sediment to develop on the monument's exteriors and also harmed other architectural elements such as arches, openings, and intricate stone carvings.

The experts also found evidence of peeling and erosion on the stonework.

"PM2.5 and PM10 are well-known as major causes to the darkening of materials subjected to outside air. This phenomenon occurs when particles build up over years, leading to noticeable blackening of these surfaces," the paper explains.

The analysis advises the early implementation of conservation strategies to protect the monument.

"Appearance of a sooty deposit is a gradual process that usually begins with a fine dark film, which can be removed, especially in the beginning," the paper notes.

It also mentions that stone protectives could be applied to severely impacted surfaces to prevent the growth of dark deposits.