Study Finds Delhi Air Pollution Coating Red Fort in 'Black Crusts'
Researchers warn that toxic air in Delhi is forming damaging black deposits on the 17th-century Red Fort’s sandstone walls.
Air Pollution Leaves Black Deposits on Red Fort
Severe air pollution in Delhi has led to the formation of black crusts on the walls of the Red Fort, one of the city’s most iconic Mughal-era monuments. Researchers say the crusts, measuring 0.05–0.5mm thick, result from chemical reactions between pollutants and the fort’s red sandstone. Without intervention, this build-up could erode its intricate carvings.
First Comprehensive Study
Between 2021 and 2023, a team from India and Italy analysed air quality data and scraped deposits from various sections of the 17th-century monument. Their findings, published in the journal Heritage, reveal that particulate matter (PM2.5 and PM10) and other airborne contaminants accelerate surface soiling and damage structural elements like vaults and arches.
Heritage at Risk
Conservation experts warn that Delhi’s heritage sites are under threat. A similar case led India’s Supreme Court in 2018 to urge measures to protect the Taj Mahal from discolouration caused by pollution.
Conservation Strategies
The study recommends early-stage cleaning of thin crust layers and the application of sealants or stone protectives to slow future deposits. Timely action could help preserve the fort’s historic carvings and facades.


The study shows that Delhi’s air pollution is actively corroding the Red Fort’s sandstone, threatening its historic carvings without immediate conservation efforts.
This topic was reported by BBC News.
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