- Delhi's severe air pollution is causing black crusts to form on the 17th-century Red Fort, threatening its intricate carvings and accelerating its decay.
- A study by researchers from multiple institutions found fine particulate matter and nitrogen dioxide are responsible, with crusts up to half a millimetre thick on walls exposed to heavy traffic.
- These crusts are composed of gypsum, bassanite, weddellite, and heavy metals such as lead, zinc and chromium, primarily originating from vehicle emissions, cement plants and construction activity.
- The findings include blistering of plastered walls, dampness, flaking sandstone, salt deposits, and a loss of detail in carvings, with black crusts causing visible discolouration and diminishing the site's cultural value.
- Researchers recommend regular cleaning and the application of protective coatings to mitigate the damage, warning that thicker deposits bond to the stone and risk permanent loss.
IN FULL