Carbon soot and dust behind discoloration of India's iconic Taj Mahal

A new study has revealed that airborne carbon particles and dust are behind discoloration of India's Taj Mahal, giving the gleaming white landmark a brownish cast.

Michael Bergin, a professor in the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology said that their team was able to show that the pollutants discoloring the Taj Mahal are particulate matter: carbon from burning biomass and refuse, fossil fuels, and dust - possibly from agriculture and road traffic and they have also been able to show how these particles could be responsible for the brownish discoloration observed.

To find out what was causing the color change, a team from four different institutions was assembled. In addition to Bergin, it included Sachchida Nand Tripathi and Tarun Gupta from the Indian Institute of Technology in Kanpur, India; K.S. Rana from the Archaeological Survey of India in Delhi; Martin M. Shafer, Ana M. Villalobos, and James J. Schauer from the University of Wisconsin's Environmental Chemistry and Technology Program, and J. Jai Devi and Michael Mckenzie from Georgia Tech.

The researchers used air sampling equipment to measure what was in the air in the Taj Mahal complex from November 2011 through June 2012. Filters from the air-sampling equipment were analyzed for both fine particulate matter (smaller than 2.5 microns in diameter) and total suspended particulate matter. The analysis was done by scientists in both India and the United States.

In addition, the researchers placed small samples of pristine marble onto the Taj Mahal at various locations near the main dome. After exposure to air pollutants over a two-month period, the samples were analyzed using an electron microscope to measure the size and the number of particles deposited on their surfaces as well as their elemental signatures. This information allowed the researchers to determine the likely composition of the particles.

The researchers found particles of dust, brown organic carbon and black carbon in the filters and on the marble samples, Bergin said. The carbon particles come from a variety of sources, including fuel combustion, cooking and brick-making, trash and refuse burning, and vehicle exhaust. The dust may come from local agricultural activities and vehicular traffic - or from distant sources.

The study was published in the journal Environmental Science and Technology.