One of India’s most treasured monuments, the Red Fort, is under threat from Delhi’s toxic air, according to a groundbreaking study that has revealed the formation of “black crusts” on the fort’s historic red sandstone walls.
The peer-reviewed research, published in the journal Heritage, is the first comprehensive scientific examination of how severe air pollution is affecting the 17th-century Mughal-era fort, which is both a UNESCO World Heritage site and a symbol of India’s independence.
Researchers from India and Italy studied air quality data between 2021 and 2023 and conducted on-site inspections, scraping off black deposits to analyze their composition. The findings are alarming: the crusts, ranging from 0.05mm to 0.5mm in thickness, are the result of chemical interactions between Delhi’s airborne pollutants — including PM2.5 and PM10 particulate matter — and the fort’s sandstone.
These deposits not only discolor the monument but could also damage intricate carvings, arches, and vaults if no action is taken soon. The study also observed flaking and blistering on several sections of the walls, signaling progressive deterioration.
“PM2.5 and PM10 are significant contributors to the soiling of surfaces exposed to ambient air,” the study notes. “This occurs as particulate matter settles and accumulates over time, leading to visible blackening and surface damage.”
The Red Fort, commissioned by Mughal Emperor Shah Jahan in 1638, is not just an architectural marvel but also a site of national pride. India’s first Prime Minister, Jawaharlal Nehru, hoisted the national flag from its ramparts on August 16, 1947 — a tradition that continues every Independence Day.
Experts say the findings underscore an urgent need for intervention. “The formation of a black crust is a progressive phenomenon that usually begins with a thin deposit that can be removed in the early stages,” the study’s authors recommend, adding that protective sealants and targeted conservation measures could help slow the damage.
This revelation comes after similar concerns about the Taj Mahal, where India’s Supreme Court in 2018 warned that the marble mausoleum had turned yellow and greenish-brown due to air and water pollution.
Conservationists are now calling on both the central and Delhi governments to act swiftly. “If we don’t implement robust conservation strategies soon, we risk losing the original character of one of India’s most important monuments,” said a heritage expert not involved in the study.
The report highlights the broader challenge of protecting India’s cultural heritage in one of the world’s most polluted cities, where air quality routinely dips to hazardous levels, especially in winter.