Air pollution in Delhi accelerating Humayun’s Tomb decay, flags IIT study

To understand how pollution affects the monument, the researchers collected five small black crust samples from rain-sheltered rooftop locations of Humayun’s Tomb under the supervision of a conservator from the Archaeological Survey of India.

4 min readNew DelhiAug 2, 2026 09:37 PM IST

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A layer of haze over Kartavya Path in New Delhi. (Express photo by Anil Sharma)

Air pollution is accelerating the decay of Humayun’s Tomb in Delhi by driving the formation of pollutant-rich black crusts on its sandstone surfaces, according to a joint study by IIT Kanpur and IIT Roorkee of the UNESCO World Heritage Site.’

The study, according to the researchers, “provides a multi-analytical evidence base to inform preventive conservation strategies and the prioritisation of cleaning and monitoring actions at this site and at comparable monuments in similarly polluted urban environments”.

Published in the International Journal of Architectural Heritage, the study was carried out by Gaurav Kumar, Bhola Ram Gurjar and Chandra Shekhar Prasad Ojha from the Department of Civil Engineering at IIT Roorkee, along with Mukesh Sharma from IIT Kanpur.

How pollution affects the monument

To understand how pollution affects the monument, the researchers collected five small black crust samples from rain-sheltered rooftop locations of Humayun’s Tomb under the supervision of a conservator from the Archaeological Survey of India.

No sandstone was removed from the monument because of conservation restrictions. Instead, only the thin black deposits that had accumulated on the stone surface were carefully collected using a scalpel, avoiding mortar joints and repaired areas to ensure that no damage was caused to the structure. The samples were collected from different orientations of the rooftop to capture how prevailing winds and environmental exposure influence pollutant deposition.

The sampling locations were chosen based on Delhi’s long-term weather patterns, explains the study. During the post-monsoon and winter months, prevailing northwesterly and westerly winds transport sulphur dioxide, nitrogen oxides, particulate matter and trace metals across the city.

According to the authors, these winds carry “urban and regional air pollutants like SO₂, NOx, PM2.5, PM10, and trace metals eastward, which favors the accumulation and growth of BC (black crust).”

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Once collected, the samples underwent a comprehensive series of laboratory analyses. The analyses showed that the black crust is dominated by gypsum, a sulphate mineral formed through atmospheric pollution, along with carbon-rich particles embedded within the mineral layer. “Combined evidence from XRF, XRD, FTIR, SEM-EDX, and CHNS analysis identifies carbonaceous rich gypsum as the signature alteration phase, accompanied by trace amounts of heavy metals indicative of atmospheric inputs,” the study said.

According to the researchers, the gypsum does not originate primarily from the sandstone itself. Instead, calcium supplied through road dust and airborne particles reacts with sulphur compounds present in polluted air to form gypsum on the monument’s surface.

The study found that the crust also contains trace metals associated with urban pollution. “Trace-element profiles further suggest regional air pollution markers, consistent with Delhi’s major emission sources, including vehicular traffic, road/soil dust, construction dust, biomass burning, and industrial activities,” the authors wrote.

The study also found that black crust formation varies across different parts of the monument depending on environmental exposure.

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The researchers reported that “gypsum was most abundant at the more wind-exposed, rain-sheltered rooftop locations and comparatively weaker at more protected areas, revealing a clear exposure and orientation related gradient in crust development.”

One of the study’s principal findings is that the “black crust [is] identified as a passive air pollution sampler at the Tomb.” In the conclusion, they write that the results “support the interpretation of BC as a passive sampler of the Delhi ambient pollution scenario”,

Calling for preventive conservation measures, the researchers state that “the formation of BC on heritage stone is a cumulative, long-term process that closely tracks regional air pollution levels. Delhi’s persistently elevated pollution burden has therefore accelerated BC accretion on local monuments.”

They conclude that “this study highlights that the monuments in Delhi require targeted preventive conservation interventions, as the megacity is currently a polluted hotspot.”

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The study recommends periodic removal of black crusts using carefully selected and scientifically established cleaning techniques, evaluation of protective coatings through site-specific trials, continued air-quality monitoring, and the use of atmospheric modelling to assess future deterioration risks.

It also suggests that reducing emissions through measures such as greater adoption of electric vehicles and lower-emission fuels could help reduce the pollutant load that contributes to black crust formation around vulnerable heritage monuments.

Vidheesha Kuntamalla

Vidheesha Kuntamalla is a Senior Correspondent at The Indian Express, based in New Delhi. She is known for her investigative reporting on higher education policy, international student immigration, and academic freedom on university campuses. Her work consistently connects policy decisions with lived realities, foregrounding how administrative actions, political pressure, and global shifts affect students, faculty, and institutions. Professional Profile Core Beat: Vidheesha covers education in Delhi and nationally, reporting on major public institutions including the University of Delhi (DU), Jawaharlal Nehru University (JNU), Jamia Millia Islamia, the IITs, and the IIMs. She also reports extensively on private and government schools in the National Capital Region. Prior to joining The Indian Express, she worked as a freelance journalist in Telangana and Andhra Pradesh for over a year, covering politics, rural issues, women-centric issues, and social justice. Specialisation: She has developed a strong niche in reporting on the Indian student diaspora, particularly the challenges faced by Indian students and H-1B holders in the United States. Her work examines how geopolitical shifts, immigration policy changes, and campus politics impact global education mobility. She has also reported widely on: * Mental health crises and student suicides at IITs * Policy responses to campus mental health * Academic freedom and institutional clampdowns at JNU, South Asian University (SAU), and Delhi University * Curriculum and syllabus changes under the National Education Policy Her recent reporting has included deeply reported human stories on policy changes during the Trump administration and their consequences for Indian students and researchers in the US. Reporting Style Vidheesha is recognised for a human-centric approach to policy reporting, combining investigative depth with intimate storytelling. Her work often highlights the anxieties of students and faculty navigating bureaucratic uncertainty, legal precarity, and institutional pressure. She regularly works with court records, internal documents, official data, and disciplinary frameworks to expose structural challenges to academic freedom. Recent Notable Articles (Late 2024 & 2025) 1. Express Investigation Series JNU’s fault lines move from campus to court: University fights students and faculty (November 2025) An Indian Express investigation found that since 2011, JNU has appeared in over 600 cases before the Delhi High Court, filed by the administration, faculty, staff, students, and contractual workers across the tenures of three Vice-Chancellors. JNU’s legal wars with students and faculty pile up under 3 V-Cs | Rs 30-lakh fines chill campus dissent (November 2025) The report traced how steep monetary penalties — now codified in the Chief Proctor’s Office Manual — are reshaping dissent and disciplinary action on campus. 2. International Education & Immigration ‘Free for a day. Then came ICE’: Acquitted after 43 years, Indian-origin man faces deportation — to a country he has never known (October 2025) H-1B $100,000 entry fee explained: Who pays, who’s exempt, and what’s still unclear? (September 2025) Khammam to Dallas, Jhansi to Seattle — audacious journeys in pursuit of the American dream after H-1B visa fee hike (September 2025) What a proposed 15% cap on foreign admissions in the US could mean for Indian students (October 2025) Anxiety on campus after Trump says visas of pro-Palestinian protesters will be cancelled (January 2025) ‘I couldn’t believe it’: F-1 status of some Indian students restored after US reverses abrupt visa terminations (April 2025) 3. Academic Freedom & Policy Exclusive: South Asian University fires professor for ‘inciting students’ during stipend protests (September 2025) Exclusive: Ministry seeks explanation from JNU V-C for skipping Centre’s meet, views absence ‘seriously’ (July 2025) SAU rows after Noam Chomsky mentions PM Modi, Lankan scholar resigns, PhD student exits SAU A series of five stories examining shrinking academic freedom at South Asian University after global scholar Noam Chomsky referenced Prime Minister Narendra Modi during an academic interaction, triggering administrative unease and renewed debate over political speech, surveillance, and institutional autonomy on Indian campuses. 4. Mental Health on Campuses In post-pandemic years, counselling rooms at IITs are busier than ever; IIT-wise data shows why (August 2025) Campus suicides: IIT-Delhi panel flags toxic competition, caste bias, burnout (April 2025) 5. Delhi Schools These Delhi government school grads are now success stories. Here’s what worked — and what didn’t (February 2025) ‘Ma’am… may I share something?’ Growing up online and alone, why Delhi’s teens are reaching out (December 2025) ... Read More

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