Air pollution is deteriorating Delhi’s Humayun’s Tomb, according to a comprehensive study conducted by researchers from IIT Roorkee and IIT Kanpur. The research found that years of exposure to polluted air have led to the formation of a damaging black crust on the UNESCO World Heritage Site, accelerating the decay of its iconic sandstone structure.

Published in the International Journal of Architectural Heritage, the study delivers scientific evidence linking urban air pollution to the long-term deterioration of one of India’s most significant Mughal-era monuments.

IIT Researchers Identify Black Crust as Major Cause of Damage

Scientists analyzed black crust samples collected from different sections of Humayun’s Tomb using advanced laboratory techniques to examine their chemical composition, mineral content, and microscopic structure.

The study found that the crust is primarily made of gypsum, which forms when sulphur dioxide in polluted air reacts with calcium-rich dust and atmospheric moisture. This layer then traps soot, metal particles, and other airborne pollutants, creating the dark coating visible on the monument today.

Key Findings of the Study

Why the Black Crust Is More Than a Cosmetic Problem

Researchers emphasized that the black crust is not simply a surface stain.

• Continuous chemical reactions beneath the deposit gradually weaken the sandstone, making it increasingly vulnerable to weathering, erosion, and structural deterioration.
• The study also observed that crust thickness varies across the monument.
• Areas protected from rainfall accumulate thicker deposits because pollutants remain undisturbed for longer periods, whereas exposed surfaces benefit from natural washing during rains, resulting in comparatively thinner crust formation.

Also Read: Google’s India Data Centre Faces Environmental Obstacles

Pollution Sources Continue to Threaten the Monument

The researchers linked the crust formation to multiple urban pollution sources surrounding Delhi. These include emissions from vehicles, industrial activities, construction dust, biomass burning, and suspended particulate matter.

According to the findings, the combination of these pollutants creates conditions that continuously promote gypsum formation, accelerating the degradation of the monument’s historic sandstone.

Also Read: Canadian Wildfires Were Twice As Likely Due To Climate Change, New Analysis Shows

Recommended Conservation Measures

The study recommends a comprehensive conservation strategy to slow further deterioration.

• Researchers suggest the periodic scientific removal of black crust deposits, continuous air quality monitoring around the monument, and careful evaluation of protective coatings before applying them to heritage structures.
• The team also stressed the importance of reducing pollution at its source through eco-friendlier transportation systems, lower-emission fuels, and stronger air quality management.

These measures would help reduce the formation of damaging deposits over the long term.

Also Read: FAO Report Calls For Stronger Peatland Emissions Monitoring And Better Data

Protecting Landmark Architectures

Air pollution is deteriorating Delhi’s Humayun’s Tomb, but the iconic Mughal monument is far from the only heritage site confronting environmental threats. Across the globe, historic landmarks are increasingly bearing the impact of pollution and climate change.

From air pollution corroding ancient marble structures in Athens to rising sea levels threatening Venice’s centuries-old architecture and extreme weather damaging archaeological sites worldwide, conserving cultural heritage has become far more complex than traditional restoration alone.

While scientists continue to study these environmental risks, protecting historic monuments is evolving into a challenge that calls for both advanced conservation techniques and stronger environmental action.

Also Read: Nationwide Study Reveals Rising Sea Levels Threaten U.S. Coastal Wetlands