Is Delhi's iconic Red Fort turning black? What the latest study tells?
The Red Fort in India's capital New Delhi is turning black. According to a study, "black layers" have formed on the walls of the Red Fort due to air pollution.
Researchers found that this black layer is formed due to chemical reaction between the fort walls made of red sandstone and pollutants. Its thickness is said to be 0.05 mm to 0.5 mm.
According to the study, these black layers can damage the fine carvings of the fort. This is the first such study, which has understood the effect of air pollution on this 17th century monument.
The research was conducted this year by scientists from Indian Institute of Technology-Roorkee, Indian Institute of Technology-Kanpur, Ca’ Foscari University of Venice and Archaeological Survey of India (ASI) as part of a collaboration between the Department of Science and Technology of India and the Ministry of Foreign Affairs of Italy.
Thickness of the black layers varied
The team analysed sandstone and black layer samples collected from various areas of the Red Fort complex, including the Zafar Mahal. The findings showed that the thickness of the black layers varied from thin deposits of about 0.05 millimetres in residential areas to thick layers of 0.5 millimetres on the walls of high-traffic areas. These thick layers are firmly attached to the stone surface, making the surface prone to chipping and destruction of intricate carvings.
According to the researchers, the black layers mainly consist of gypsum, basanite, weddellite and small amounts of heavy metals such as lead, zinc, chromium and copper. These pollutants are not naturally found in the sandstone but are deposited from external sources, such as vehicular emissions, cement factories and construction activities in the city.
Chemical reactions between pollutants lead to formation of gypsum layers
The study highlights how chemical reactions between pollutants such as sulphur dioxide and nitrogen oxides lead to the formation of gypsum layers, which eventually cause damage during rainfall. After obtaining air quality data from the Central Pollution Control Board for the years 2021 to 2023, the researchers confirmed that the concentration of fine particles was two and a half times higher than the national limit, while coarse particles were three times higher than the limit. Nitrogen dioxide levels also exceeded safe limits, causing the stone to rot slowly, while ammonia and sulfur dioxide levels were within limits.
Delhi is one of the most polluted cities in the world. During the winter season, Delhi often remains in the headlines for its poor air quality.