By Cherylann Mollan

Copyright bbc

The researchers studied Delhi’s air quality data between 2021 and 2023. Then they scraped off the black crust found on various walls of the fort and examined its composition.

They found that particulate matter and other pollutants in the air had caused the black sediment to form on the fort’s walls and also damaged other architectural elements such as vaults, arches and delicate stone carvings.

The researchers also found evidence of blistering and flaking on the walls.

“PM2.5 and PM10 [types of particulate matter] are widely recognised as significant contributors to the soiling of surfaces exposed to ambient air. This phenomenon occurs when particulate matter settles and accumulates over time, leading to visible discolouration and blackening of these surfaces,” the study notes.

The study recommends the timely implementation of conservation strategies to protect the fort.

“The formation of a black crust is a progressive phenomenon that usually begins with a thin black layer or deposit, which can be removed, at least in the early stages,” the study notes.

It also says that stone protectives or sealants could be applied to highly-affected areas to slow down or prevent the formation of black crusts.