Brown Carbon and Dust Gives Taj Mahal The Blues and Discolouration Hues

Brown Carbon and Dust Gives Taj Mahal The Blues and Discolouration Hues

A study published by Indian scientists in collaboration with Americans has revealed the reason behind the discolouration of the white marble of the Taj Mahal. It is specifically the blue light absorbing dust particles and carbon particles which plays a major role in causing the Taj Mahal to lose its beautiful colouring.

How the Taj Mahal Lost Its Shine?

Particulate carbon and fine dust particles are causing the marble to become brown. Specific pollutants in the air have led to the discolouration of the white marble of which the Taj Mahal is composed. Specifically, the particulate carbon and fine dust particles deposited on the marble lead to its browning.

A Tale of Two Carbons

Specifically, carbon is of two types namely black carbon as well as light absorbing carbon/brown carbon. The results of this study were also published in the journal entitled Environmental Science & Technology. Apart from studying air samples which are collected from the area, the research scientists conducting the study also used marble samples on the buildings for collecting the pollutants. Computer modelling was also undertaken to study the colour change which has been brought about by reflectance of the particles.

Organic carbon as well as dust particles contain the capability to specifically and preferentially taken in light from the blue region of the spectrum. Absorption of the blue light by these pollutants causes the marble surface to change into its current brown colour.

How The Taj Mahal Got the Blues?

“There is one group of organic carbon which absorbs light in the blue region of the spectrum and this is called brown carbon. Discolouration is because of what is happening to reflectance, and reflectance is in turn influenced by these particles,” Prof. S.N. Tripathi, who is one of the study’s lead authors and part of the Department of Civil Engineering and Centre for Environmental Science and Engineering, Indian Institute of Technology (IIT), Kanpur has been quoted as saying.

Haematite Spurs Blue Light

The ability of fine dust particles to product a brown hue is a well established fact in India. It is the presence of a substance known as haematite which is responsible for the brown hue in the dust. “If haematite is not present in the dust then the dust would be only scattering in nature,” Tripathi also said. Haematite is an ingredient which absorbs the blue wavelength of the spectrum.

The absorption of the blue light by independent dust particles is smaller than that of brown carbon, but given that the dust of two micron size found in this matter increases the absorption rate more than brown carbon, it is obvious that the combination of the two will prove deadly for Mumtaz Mahal’s final resting place.

The study also showed that particles bigger than 2 micron in size constituted about 70% of the deposited particle surface area. The mostly coarse particles are the dust particles which are causing the damage. Pure dust particles lack the capability to stick to the surface.

“But what we see is a potpourri of particles. The organic carbon is very sticky,” he also said,

Combined Effect of Dust and Carbon

As against the dust particles, carbon particles are within 100 nanometre to 1 micron size. The basic sources of brown as well as black carbon are burning of biomass, crop and trash residue. In other words, fossil fuel combustion leading to production of toxic gases is causing the national heritage building to lose its brilliant white hue.

Researchers who studied the marble samples found black carbon resulted in a greyish discolouration while brown carbon and dust combined to produce the yellow brown hues characteristic of the discolouration of the Taj Mahal.

“We found the colour of surrogate marbles matched well with model results. Modelling showed the combined effect of dust and carbon in discolouration of the marble samples,” Tripathi said.

Institutions Behind this Landmark Study

The Georgia Institute of Technology, the University of Wisconsin as well as IIT-K and Archaeological Survey of India have joined hands to collaborate for this unique study.

"Our team was able to show that the pollutants discolouring the Taj Mahal are particulate matter: carbon from burning biomass and refuse, fossil fuels, and dust - possibly from agriculture and road traffic," Georgia Tech School of Earth and Atmospheric Sciences’ Michael Bergin was quoted as saying.

About the Historic Taj Mahal

The Taj Mahal was constructed in the 1600s by Mughal Emperor Shah Jahan for honouring his wife Mumtaz Mahal. This marble structure is her final resting place. The historic Taj Mahal has a marble dome which measures 115 feet in height with minarets that are 130 feet in height.

The Taj Mahal has become a UNESCO World Heritage Site since 1983. It was during the 1970s that there came to be a brownish hue on the white marble of the structure. For cleaning this so far, a mud pack therapy is being used. While air pollution was always suspected to be a culprit, no studies have been done for confirming this till now.

From White Marble to Brown Discolouration

The present research study was conducted using special equipment and air samples surrounding the Taj Mahal from the month of November in 2011 to the month of June in 2012. Small samples of fresh marbles were also placed at various points of the Taj Mahal.

The air sampling filters and samples of marble taken from the heritage building indicated that the Taj Mahal was exposed to dust as well as black and brown carbon. The researchers hold that the dust came from agricultural activities as well as traffic and carbon emanated from various sources such as car exhaust and burning of trash.

No Solution in Sight

The Archaeological Survey of India has said that the mud pack therapy is conducted on the Taj Mahal each year instead of 5 to 6 years now. But this poses a problem as the building has to be closed from public viewing during this process. Moreover, too frequently done, this mud pack therapy can permanently ruin the original colour of the building.

Unless the issue is resolved, the Archaeological Survey of India said that it might have to do the mud-pack therapy on the Taj Mahal yearly, when it was only previously done once every five to six years. While the therapy is currently effective, the process takes days to complete, wherein the Taj Mahal is closed to visitors. In addition, repeated usage of the process could permanently remove the original colour of the Taj Mahal.