Loss in details of carvings, blistering of walls: Red Fort facing damage due to air pollution, flags study

The research, published in Heritage journal, has been carried out under a collaboration between India’s Department of Science and Technology and Italy’s Ministry of Foreign Affairs (MAECI) and was conducted by scientists from IIT Roorkee, IIT Kanpur, Ca’ Foscari University of Venice, and the Archaeological Survey of India (ASI).

The study’s aim was to study the chemical composition of the back crusts affecting the conservation of the Red Fort complex and to investigate their likely origin. Black crusts are often considered one of the biggest threats to the degradation of outdoor cultural heritage buildings (CHBs), the study underlined. These, the research has pointed out, are abundantly present around the walls of the monument.

Among the significant findings of the study included the presence of high concentrations of heavy metals in the black crust samples which the researchers said possibly arose from burning of fossil fuels, wear and tear of vehicles, mechanical parts, vehicular traffic, particulate matter and soil or dust.

The samples of red sandstone predominantly consisted of quartz and microcline, while the black crusts mainly consisted of gypsum, bassanite, weddellite, quartz, and microcline. The study linked the formation of gypsum to exogenous sources such as construction activities and cement factory emissions.

The study has emphasised that long-range air pollution datasets, combined with real-world case study applications, are crucial for analysing the impact of air pollution on CHBs.

The formation of a black crust can be removed at least in the early stages without significantly damaging the stone’s integrity— a maintenance cleaning program for the most affected areas and the application of stone protectors could prevent or at least slow down the formation of a black crust, the study has recommended.

To conduct the study, the researchers took samples from the fortification wall, adjacent to the heavily trafficked Mahatma Gandhi Road, and the Zafar Mahal building within the Red Fort complex.

The researchers looked at the pollutant levels from various monitoring stations near to the Red Fort area, as per data provided by the Central Pollution Control Board between 2021 and 2023, noting that the PM2.5, PM10, and NO2 levels exceeded the National Ambient Air Quality Standards (NAAQS). The study emphasised that higher annual average concentrations of PM10 pose ongoing threats to the Fort. The annual average concentration of NH3 and SO2, however, improved, but the researchers noted that even lower levels of SO2 can accelerate the degradation of stone and metal structures.

On soiling of the surfaces exposed to ambient air with PM2.5 and PM10, the study said, “This phenomenon occurs when particulate matter settles and accumulates over time, leading to visible discoloration and blackening of these surfaces. The effect is particularly evident on intricate carvings and architectural details, where particulate matter not only causes visible damage but also diminishes the cultural and aesthetic value of these sites.”

Pollutants deposit on architectural surfaces, blackening and also initiates a sulfation process on the stone’s surface, where calcite reacts with sulfate ions in the atmosphere to create a gypsum layer. NOX acts as a catalyst for oxidation and further accelerates the stone degradation.
The study also highlighted that soluble nitrate can infiltrate the stone during crystallization and cause internal stress leading to cracks within the stone structure.

The Fort’s perimeter was originally protected by a 9 metre moat on three sides, while its eastern side faced the Yamuna River. However, the river’s course has since been altered, and the area is now occupied by the Inner Delhi Ring Road, which experiences heavy traffic.