Chuck Bednar for redOrbit.com – Your Universe Online
The white marble that has helped make India’s Taj Mahal such an iconic structure has been turning yellowish brown in recent years, and now researchers have discovered the cause – black carbon and brown carbon resulting from the burning of trash, fuels and other materials.
Writing in a recent edition of the journal Environmental Science & Technology, scientists from Georgia Tech, the University of Wisconsin-Madison, the Indian Institute of Technology and the Archaeological Survey of India found that these pollutants are responsible for the grime that has forced workers to apply a clay mask to the structure every few years.
In a statement, the American Chemical Society (which publishes the journal in which the new paper appears) said that the findings “could help inform efforts to protect the mausoleum and other surfaces from pollution.”
The authors of the study note that Indian officials have tried to reduce the effects of these airborne pollutants on the archaeological wonder by limiting nearby traffic and placing strict limits on local industrial emissions. Even so, the domes and minarets at the Taj Mahal have continued to collect soot, yet there had been no research into the pollutants responsible.
Michael H. Bergin, a professor at the Georgia Tech Schools of Civil and Environmental Engineering and Earth and Atmospheric Sciences, Sachchida Nand Tripathi, a professor in the Department of Civil Engineering and adjunct Professor in the Department of Earth Sciences at Indian Institute of Technology, and their colleagues set out to change that.
They analyzed particles in the air and on marble samples near the main dome at the Taj Mahal over the course of several months to find out what was causing it to appear yellow. Using a novel method they developed, the researchers estimated how those speck reflected light and altered the building’s color.
Specifically, they collected samples of ambient particulate matter and found that they contained relatively high concentrations of light-absorbing particles capable of potentially discoloring the Taj Mahal’s marble surfaces. The substances they found included black carbon and brown carbon (also known as light-absorbing organic carbon) and dust.
“Analyses of particles deposited to marble surrogate surfaces at the Taj Mahal indicate that a large fraction of the outer Taj Mahal surfaces are covered with particles that contain both carbonaceous components and dust,” the study authors wrote.
“We have developed a novel approach that estimates the impact of these deposited particles on the visible light surface reflectance, which is in turn used to estimate the perceived color by the human eye,” they added. Their results indicated that “deposited light absorbing dust and carbonaceous particles,” including black carbon and brown carbon from the combustion of fossil fuels and biomass, were responsible for the landmark’s surface discoloration.
Specifically, UPI reports indicate that approximately 30 percent of the pollutants on the marble surface of the Taj Mahal were organic carbon released by the burning of trash. Roughly three percent were black carbon, which is typically found in automobile exhaust – a surprising find, since motor vehicles are not allowed within 500 meters (1,640 feet) of the landmark.
“Overall, the results suggest that the deposition of light absorbing particulate matter in regions of high aerosol loading are not only influencing cultural heritage but also the aesthetics of both natural and urban surfaces,” Bergin, Tripathi and their colleagues wrote. They believe that their findings could be used to address the chronic yellowing and improve overall air quality.
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