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Extreme atmospheric contamination in India's capital city of New Delhi has caused the development of sooty deposits on the walls of the Mughal-era structure, a new study finds.

Scientists discovered that these crusts—formed due to chemical interactions between contaminants and the stone building—were ranging from 0.05mm and 0.5mm deep, and could damage its elaborate designs if preventive steps are taken.

This research is the initial of its category to comprehensively analyze the effects of polluted air on this 17th Century monument.

Heritage advocates have often warned about the damaging impact of environmental degradation on heritage structures in the city and multiple other regions.

A few years ago, courts observed that the Taj Mahal—a well-known historic structure—had yellowed due to environmental factors, prompting timely conservation actions.

The research on the monument, released in a academic journal in mid-2024, was carried out from 2021 and 2023 by specialists in multiple countries.

The historical site, constructed by ruler Shah Jahan, is one of Delhi's most significant tourist attractions.

India's initial leader Nehru unfurled the national flag from the fort on August 16 1947, just after sovereignty from colonial powers was declared. Since then, heads of state have been giving speeches on August 15 from the walls of the structure.

Experts analyzed Delhi's atmospheric data from recent years. They then scraped off the black crust detected on various areas of the fort and examined its content.

They found that pollutants and other elements in the atmosphere had resulted in the dark crust to appear on the structure's exteriors and also harmed other details such as vaults, doorways, and delicate artwork.

The team also found signs of blistering and flaking on the stonework.

"PM2.5 and PM10 are widely recognised as significant causes to the discoloration of surfaces subjected to outside air. This occurrence occurs when particles settle over years, leading to observable discolouration of these surfaces," the paper states.

The research advises the prompt application of preservation methods to preserve the fort.

"Development of a sooty deposit is a ongoing process that typically begins with a slight black layer, which can be removed, especially in the initial phases," the study states.

It also mentions that sealants could be used to severely impacted sections to slow down the growth of black crusts.