ShakshiThe Red Fort, known worldwide for its majestic red sandstone walls, is facing a shocking transformation. Recent scientific studies reveal that the monument is slowly losing its signature red colour and turning black. The reason is clear and deeply concerning, as air pollution is damaging Red Fort at an alarming pace. The toxic air that already harms Delhi’s residents is now eating away at one of India’s most treasured heritage sites. As leaving behind black crusts and erodes its historic beauty.
This is concerning news because air pollution in Delhi is typically associated with respiratory problems, cardiovascular diseases, and environmental harm. However, it is becoming increasingly clear that polluted air is also accelerating the decay of cultural heritage sites. The Red Fort’s transformation from vibrant red to dark black is a warning sign that air pollution’s impact extends beyond human health. As it is affecting our shared history and architectural legacy.
How is air pollution damaging the Red Fort?
A collaborative study between Indian and Italian scientists has confirmed that pollutants in Delhi’s air are contributing to the formation of black crusts on the walls of the Red Fort. The research, which involved institutions like IIT Roorkee, IIT Kanpur, and Ca’ Foscari University of Venice, analysed the sandstone surface of the monument as well as air quality data from 2021 to 2023.
The study found that concentrations of fine particulate matter (PM2.5 and PM10) were more than two and a half times above the limits set by India’s National Ambient Air Quality Standards. Elevated levels of nitrogen dioxide were also recorded, contributing to the faster decay of the red sandstone structure.
Laboratory analysis showed that the black crusts on the Red Fort’s surfaces composed of pollutants. Such as gypsum, quartz, and heavy metals like lead, copper, and zinc. These crusts particularly thick in areas exposed to vehicular emissions, construction dust, and industrial pollutants. Measurements revealed that the black layer could range from 0.05 mm in sheltered sections to as much as 0.5 mm in highly trafficked zones.
What is causing air pollution, and is that affecting the Red Fort’s colour?
Do you know what is causing the red fort to turn black? The major reason is pollution, but from where this pollution is coming, and what major parts of pollution are causing it to turn black? The primary contributors to the worsening air quality around the Red Fort include:
- Vehicular Emissions
These are major sources of nitrogen dioxide, carbon monoxide, and particulate matter. Delhi’s growing number of vehicles adds heavily to the pollution load. - Industrial Activities:
Industries around Delhi release sulfur dioxide, heavy metals, and other harmful gases into the atmosphere. This settles on buildings and monuments. - Construction Dust
Ongoing construction projects in and around Delhi lead to increased dust levels, which contribute to particulate pollution. - Biomass Burning:
During certain seasons, agricultural fires and other forms of biomass burning release fine particles that further degrade air quality.
How air pollution is damaging the Red Fort and resulting in blackening?
These are findings specifically relating to pollution & damage to the Red Fort or similar monuments, or how pollutant levels correlate with decay.
| Finding | Details |
| Black crusts composed of pollutants | The study “Characterisation of Red Sandstone and Black Crust to Analyse Air Pollution Impacts on a Cultural Heritage Building: Red Fort, Delhi, India” finds that black crusts are forming on red sandstone. These crusts contain gypsum, quartz, and heavy metals (lead, copper, zinc). |
| Exceeding pollutant standards | PM2.5, PM10 and NO₂ levels around Red Fort exceed the National Ambient Air Quality Standards (NAAQS). Even though SO₂ and NH₃ were somewhat better, even relatively low SO₂ contributes to stone damage. |
| Types of damage observed | Loss of fine details in carvings due to surface soiling and black crust formation.Blistering of plastered walls and vaults.Dampness inside arches, salt efflorescence (salt deposits) inside inner parts.Patinas (surface changes/film) on entrance doors. |
| Chemical effects | Sulphur dioxide (SO₂) and nitrogen oxides (NOₓ) react with rain or moisture to form acids (sulphuric acid, nitric acid) that erode the sandstone. Gypsum layers form and are washed off, causing surface loss. Nitrates and oxalates infiltrate stone, causing internal stress and cracking. |
| Extent relative to national standards | Pollutant levels are more than 2.5 times above national limits for fine particles. Coarser particles (PM10) exceed thrice the safe thresholds in many cases. |
Why Protecting Heritage Sites Matters and Are Other Monuments in Danger?
The Red Fort is not just a tourist attraction. It represents centuries of India’s history, culture, and architectural brilliance. When air pollution blackens and erodes its sandstone walls, the loss goes far beyond appearance. It weakens the structural integrity of a monument that has stood for more than three centuries.
Once the damage caused by pollution becomes irreversible, restoration work becomes far more complex and costly. Continuous exposure to particulate matter, sulfur dioxide, and nitrogen oxides means that if immediate action is not taken, monuments like the Red Fort will suffer permanent damage.
This issue is not limited to Delhi. India’s cultural heritage spans thousands of sites across the country. And many are located in cities struggling with poor air quality. According to AQI.in’s 2024 report, 94 Indian cities are among the top 100 most polluted globally in the list of the world’s most polluted. This places countless heritage monuments under constant environmental stress.
The Taj Mahal in Agra, for example, has faced visible yellowing and brown discolouration of its marble due to pollution and soot deposition. Other historic structures in cities such as Varanasi, Jaipur, and Lucknow also face risks as rising levels of fine particulate matter and industrial emissions accelerate the wear and tear of delicate carvings, murals, and stonework.
Protecting these heritage sites is not only about preserving tourist attractions. But also about safeguarding cultural memory, identity, and history for future generations. India risks losing some of its most important symbols of heritage to the invisible but powerful force of polluted air. Because of the lack of stronger pollution control measures and conservation strategies.
How Much are the Restoration Costs for Heritage Sites in India?
1. Taj Mahal, India
The Archaeological Survey of India (ASI) has undertaken significant restoration projects at the Taj Mahal. For instance, the estimated cost for replacing 400 decorative stones around the main dome was approximately ₹22 lakh. Additionally, repairs to the minarets and the Shahi mosque’s finial, damaged during a storm, were estimated at ₹60 lakh.
2. Red Fort, Delhi
The ASI allocated over ₹15 lakh for the restoration of Rang Mahal within the Red Fort. This included removing dust and dirt from the monument’s surface and preserving existing paintings with lime wash removal.
3. Kundrandar Temple, Tamil Nadu
In 2023, ₹12 lakh was allocated for the maintenance of the ancient Kundrandar rock-cut cave temple in Pudukottai district, Tamil Nadu. The Archaeological Survey of India (ASI) carries out periodic maintenance based on available resources and legal provisions outlined in the Ancient Monuments and Archaeological Sites and Remains Act, 1958.
Final Thoughts
The transformation of the Red Fort from red to black is not just a local issue or a concern for historians. It is a reflection of how air pollution is quietly affecting cultural landmarks and endangering our shared heritage. As Delhi’s air quality remains in the moderate to poor range, action is needed now to safeguard not only public health but also historical treasures that define the identity of the nation.
Monitoring air quality through platforms like AQI.in helps raise awareness and provides actionable insights for policymakers, conservationists, and the general public. Together, informed choices can help to reduce pollution and ensure that future generations can admire the Red Fort in its original glory.
Manasvi Kumar
Deepshikha Deb
Shikhar Verma
Poorna Khanna
Livia Machado
Gyane Haobijam
Divya Singh