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Severe atmospheric contamination in the nation's capital city of Delhi has resulted in the appearance of dark layers on the walls of the Red Fort, a new study finds.

Scientists found that these deposits—formed due to chemical interactions between contaminants and the sandstone fort—were between 0.05mm and 0.5mm deep, and could harm its detailed artwork if no action implemented.

This research is the first of its category to extensively examine the effects of environmental contamination on this 17th Century site.

Heritage advocates have repeatedly alerted about the damaging influence of contamination on heritage structures in the capital and multiple other regions.

Previously, courts observed that the white marble monument—another 17th Century site—had discolored due to environmental factors, prompting swift restoration actions.

The analysis on the Red Fort, shared in a academic journal in recent months, was performed from 2021 and 2023 by experts in international institutions.

The iconic fort, built by Mughal Emperor Shah Jahan, is one of the city's most prominent cultural landmarks.

India's first Prime Minister Jawaharlal Nehru hoisted the tricolor from the monument on 16 August 1947, a day after sovereignty from Britain was declared. Ever since, heads of state have been giving addresses on Independence Day from the walls of the fort.

Experts analyzed Delhi's air quality data from a three-year period. They then scraped off the black crust present on multiple areas of the fort and tested its composition.

They discovered that particulate matter and other contaminants in the atmosphere had led to the dark crust to develop on the fort's walls and also damaged other details such as vaults, openings, and delicate designs.

The team also identified signs of swelling and chipping on the surfaces.

"PM2.5 and PM10 are well-known as key contributors to the darkening of surfaces subjected to outside air. This occurrence happens when particles accumulate over time, causing observable discolouration of these surfaces," the study notes.

The study recommends the prompt use of protective measures to protect the site.

"The formation of a sooty deposit is a progressive process that often begins with a slight sooty coating, which can be removed, at least in the early stages," the report adds.

It also mentions that stone protectives could be applied to vulnerable surfaces to slow down the development of sooty layers.