Tourists and pilgrims are periodically disappointed to find that the Taj Mahal is not the iconic white palace pictured in countless postcards, movies and music videos, but a muddy shade of brown. Sometimes, visitors even find that the walls of the palace are covered in mud—the only cleaning method that seems to restore that architectural wonder to its former state of pearly glory.
Mike Bergin, a researcher at the Georgia Institute of Technology, was one such disappointed tourist. Bergin was surprised to find sections of the UNESCO-listed palace covered in clay, but he was even more shocked to discover that no one knew the source of the pollution it was meant to remove, ScienceNOW writes. Some speculated that the discoloration was caused by sulfurous gas, others pointed to droplets deposited by fog, which then oxidized on the stone's surface. Bergin decided to find out for sure.
For a year, he and several colleagues from Georgia Tech and India measured ambient particle concentrations in the air around the palace and collected samples from its walls, hypothesizing that the pollution must be particulate and water insoluble, given its refusal to budge when sprayed with water or rained on, ScienceNOW describes. Sure enough, the team determined that the particles came from vehicle emissions, cooking smoke, dust and frequent fires set to burn garbage and animal waste. The particles, ScienceNOW adds, absorb UV that turns them a brownish shade, thus marring the Taj Mahal's pristine walls.
The region's heavy air pollution, the team concludes, is "not only influencing cultural heritage but also the aesthetics of both natural and urban surfaces" and, as ScienceNOW adds, human health, too.