New Delhi, Sept. 16 -- Delhi's air quality is threatening Red Fort as it is facing gradual and accelerating damage. A study, titled Characterisation of red sandstone and black crust to analyse air pollution impacts on a cultural heritage building: Red Fort, Delhi, has revealed that black crusts of pollutants are steadily forming on the red sandstone walls of the 17th-century monument, threatening its structural and aesthetic integrity.

Strangely, no studies have focused on characterising its constituent materials or the degradation phenomena taking place. According to the researchers, the black crusts primarily consist of gypsum, bassanite, weddellite, and trace amounts of heavy metals such as lead, zinc, chromium, and copper. These poll...