Ancient stones meet modern pollutants: How air pollution is eroding India’s heritage monuments

The implications of air pollution on health, education and work productivity dominate the headlines every winter, when air quality levels deteriorate to hazardous levels over north India. However, new research reveals that these pollutants are also slowly corroding the symbols of our past and putting our heritage at risk.

In a scientific study on the Red Fort, scientists have found that chemical interactions between pollutants and the monument's stone surface are slowly destroying its distinctive red façade and turning it black.

It confirms what was already known about how pollution chips away at a monument's integrity, when it was discovered decades ago that pollution was behind the Taj Mahal's changing appearance. Despite protections, this “wonder of the world” continues to find itself in the news for foul smells and its marble turning green.

The Red Fort has been a lasting political symbol and has served as the backdrop of every Prime Minister's Independence Day speech since 1947. But political will is failing to save the fort – and hundreds of other monuments in the region – from the ill-effects of air pollution. The Red Fort study is the first to attribute the formation of black crusts on its surface to emissions from cement factories, thermal power plants, and vehicles.

“Indian monuments are already losing their settings because of rampant encroachment and unauthorised construction. It's sad to see policymakers believe there is a Planet B. Otherwise, there would have been some concrete measures to reduce air pollution,” says Abha Narain Lambah, a UNESCO award-winning conservation architect.

Not all is lost, however. Early interventions can prevent airborne damages to heritage buildings, the researchers of the Red Fort study say.

Most of the world's ancient monuments are made of limestone and marble, which studies say were favoured materials for their local availability, durability, and ease of extraction. The historic Mughal structures in Delhi, including the Red Fort, Qutub Minar, and Humayun's Tomb, are made of Vindhyan sandstone and Makrana marble.

These materials are now facing a test of endurance amid rapid industrialisation. High levels of particulate matter and atmospheric nitrogen dioxide from traffic and factory emissions have initiated a sulfation process on the Red Fort's sandstone surface. This causes a thin layer of gypsum (calcium sulphate) to form, which, over time develops into a black crust, trapping dust and other particles, the study revealed.

“Even at low levels, the presence of nitrogen dioxide in the atmosphere accelerates the sulfation phenomenon as it acts as an oxidising agent in the degradation process,” says the study. In addition to the visible damage, erosion diminishes the cultural and aesthetic value of heritage sites, the study adds.

However, early restoration interventions can go a long way in preventing degradation. “We always begin the conservation process using non-abrasive methods that don't damage the fabric of the stone,” explained Lambah. “Gentle water misting under guided pressure, or techniques like multani mitti or paper poultices are also included. Chemical peeling is used only when we see a persistent accumulation of grime, and that too under supervision.”

Sanjay Kumar Manjul, Additional Director General at the Archaeological Survey of India and an author of the Red Fort study, says the ASI has already begun restoration work on the Fort. “Every product has a chemical compound. What we have to be careful about is the dosage, how much of the chemical we are using and how that quantity will react with the surface. Even a safe material like multani mitti has mineral compounds,” he says.

The ASI is now studying the impacts of air pollution on the Konark Sun Temple in Odisha, which is made of chlorite, laterite and the khondalite stones.

For MC Mehta, the lawyer who fought to protect the Taj Mahal from pollution, restoration can only go so far if emission sources are not controlled. “Even after 40 years since my case highlighted the monument's slow deterioration due to air pollution and several hearings later, nothing much has changed,” the lawyer, whose case was responsible for setting up the Taj Trapezium Zone, a defined area around the monument to protect it from pollution, in 1996, told Mongabay-India.

The Taj Trapezium Zone prohibits the operation of coal and coke-based industries within a 10,400 square kilometre area, covering the districts of Agra, Mathura, Etah, Hathras, and Firozabad in Uttar Pradesh, and Bharatpur in Rajasthan. The idea was to reduce the Taj's exposure to air pollution by pushing industries outside this boundary.

Helmed by Agra's Commissioner, the Taj Trapezium Zone core body comprises members from multiple departments, including the District Magistrates of all TTZ cities, pollution control board authorities, ASI representatives, and officers from the state ministries of environment and petroleum and natural gas. The Taj Trapezium Zone Authority has the powers to enforce compliance of fuel quality standards, and take preventive measures such as stopping electricity and water supply to polluting industries to ensure environmental protection in this zone.

Every month, a meeting is supposed to be held at the district level to assess vehicular and industrial pollution, construction activities and other related issues. In addition, quarterly Taj Trapezium Zone meetings, led by the Commissioner, add another layer of decision-making and coordination. Despite this long-standing regulatory framework, pollution levels around the Taj have risen. A recent RTI revealed that the high levels of suspended particulate matter around the mausoleum have continued to yellow the marble for almost two decades.

“A major challenge we face is the rapid development around the Taj,” said Amit Mishra, Regional Officer, Uttar Pradesh Pollution Control Board, which is a member of the Taj Trapezium Zone. “Our monitoring systems show a sharp rise in PM2.5 levels, mainly due to vehicular emissions. The number of vehicles has increased in recent years. To reduce that load, construction for the Agra Metro is underway, but that also contributes to dust pollution.”

In May, The National Green Tribunal observed lapses in implementing measures to curb air pollution in Agra. The tribunal pointed out that initiatives like planting trees, launching electric buses and building peripheral highways remained on the paper in the zone.

“Two things are important for execution: Enforcement of the law and the commitment of officials towards safeguarding not just the Taj but the entire TTZ that is home to several heritage monuments,” said Mehta.

Rising vehicular emissions are proving to be a challenge in Delhi too, where more than 7,00,000 new cars were registered in 2024. Across the country, more polluting SUVs have emerged as the preferred choice among customers. Exhaust fumes from combustion engines have contributed to the deposition of heavy metals on the black crusts forming on the Red Fort, including lead, titanium, and nickel.

An analysis by the Centre for Science and Environment found vehicles contributed between 20 and 41 percent of annual PM2.5 levels in Delhi. Other year-round emission sources include industries, coal-based power generation, construction, and waste generation. The analysis is based on studies by the Indian Institute of Technology, Kanpur, The Energy Research Institute, Indian Institute of Tropical Meteorology among other data sources.

Pollution levels have remained stagnant in the National Capital Region despite an increase in consumption, population, and energy demands, says Sunil Dahiya, founder and lead analyst at Envirocatalysts. “That reflects that something has been done, but not aggressively enough to tackle the health emergency.”

Delhi's high pollution load is partly due to its land-locked geography, which makes dispersal of pollutants difficult. “It is very evident that if pollution levels are to be reduced, we have to go for absolute emission load reduction. Till today, there hasn't been any direction or policy that focuses on this aspect. The pollution monitoring bodies have access to all data and tools, but this hasn't translated into effective implementation,” he adds.

Like the Taj Trapezium Zone, the air quality around the Red Fort is also governed by an inter-state body, the Commission for Air Quality Management. Despite having been in force for over four years, the Commission for Air Quality Management's directives have not led to a decisive reduction in pollution loads. A media report found that emissions from vehicles garnered the least attention by the Commission for Air Quality Management, despite it being the biggest year-round source of pollution.

Sohail Hashmi, eminent historian who leads heritage walks to the Red Fort and other historic monuments, says public participation is key to reducing pollution loads and advocating for India's shared history. “If we learn to value our heritage, then both the government and the people must act in an organised manner to contain pollution. An affordable, efficient public transport network is essential, and so is the willingness to embrace carpooling,” he says.

“Unless we know where we have come from, how do we plan, where do we want to go? If we have no idea of our architectural tradition, which has evolved over thousands of years, how will we connect our present life with our tradition?” asks Hashmi.

Source: Scroll
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