IIT Study Reveals Air Pollution Is Damaging Humayun's Tomb Structure Rapidly

Air pollution is accelerating the deterioration of Humayun’s Tomb, with a black crust formed on the monument’s sandstone surfaces weakening the historic structure, according to a joint study by researchers from IIT Roorkee and IIT Kanpur. The study found that years of exposure to polluted air have caused chemical changes on the UNESCO World Heritage Site, threatening the long-term preservation of one of Delhi’s most important architectural landmarks. Published in the International Journal of Architectural Heritage, the research analysed black crust samples collected from different sections of Humayun’s Tomb.

Scientists used laboratory techniques to study the samples’ chemical composition, mineral content and microscopic structure to understand how pollution has affected the monument’s sandstone. The researchers found that the black crust is primarily composed of gypsum, a mineral that forms when sulphur dioxide present in polluted air reacts with calcium-rich dust and moisture on the monument’s surface. This chemical process creates a dark layer over the sandstone, gradually altering the appearance and physical condition of the structure. According to the study, the gypsum layer acts as a trap for soot, dust and tiny metal particles released from various pollution sources, including vehicle emissions, construction activities, road dust, biomass burning and industrial pollutants.

Over time, these materials accumulate and create the black deposits visible on parts of the monument. The researchers highlighted that the black crust is not merely a visual problem or surface discolouration. The chemical reactions involved in its formation gradually weaken the sandstone, making it more vulnerable to weathering and long-term damage. The findings provide scientific evidence linking air pollution with the deterioration of historical structures in urban environments. The study observed that the thickest black crust deposits were found in rain-sheltered areas of Humayun’s Tomb, where pollutants can accumulate for longer periods without being naturally removed.

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In contrast, surfaces more exposed to rainfall showed comparatively thinner deposits because rainwater helps wash away some pollutants from the monument. Researchers said the findings could assist conservation authorities in developing targeted strategies to protect the monument. They recommended regular removal of black crust deposits through scientifically tested conservation methods, continuous monitoring of pollution levels around the site and careful evaluation of protective coatings before their application.

The study also suggested that reducing pollution at its source would be essential for long-term preservation. Measures such as cleaner transportation systems, lower-emission fuels and better control of industrial and construction-related pollution could help slow the formation of harmful deposits on heritage structures. Humayun’s Tomb was built in the 16th century by Empress Bega Begum in memory of Mughal emperor Humayun. Considered India’s first grand garden tomb, the monument introduced several architectural features that later influenced Mughal architecture, including the design elements seen in the Taj Mahal.

The red sandstone and white marble structure was declared a UNESCO World Heritage Site in 1993 and remains one of Delhi’s most visited historical monuments. Its architectural design, garden layout and influence on later Mughal buildings have made it an important part of India’s cultural heritage. The latest research highlights the growing challenge of protecting historic monuments located in heavily polluted urban areas. Experts believe that combining scientific conservation techniques with stronger pollution control measures will be necessary to preserve Humayun’s Tomb and ensure that future generations can continue to experience its architectural and historical significance.

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