New Delhi, Oct. 6 -- Delhi's iconic 17th-century Red Fort, a UNESCO World Heritage Site and symbol of India's rich Mughal heritage, is showing signs of distress, and the culprit is the city's worsening air pollution. Scientists have found that the monument's signature red sandstone is gradually turning black due to a chemical reaction triggered by pollutants in the air.

A joint study by Indian and Italian researchers has revealed that 'black crusts', layers of pollution deposits containing compounds like gypsum, quartz, and heavy metals such as lead, copper, and zinc, are forming on the fort's surface. These crusts not only darken the walls but also erode the stone, threatening the monument's long-term stability.

The study, conducted be...