NEWS

Finally, the specific pollutants in the air that are responsible for the discoloration of the white marble of Taj Mahal have been identified. Particulate carbon and fine dust particles that are deposited on the marble are responsible for its browning. Carbon is of two types — black carbon and light absorbing organic carbon or brown carbon. The results from a study were published a few days ago in the journal Environmental Science & Technology. Besides studying air samples collected from the area, the authors used marble samples on the building to collect the pollutants. They also undertook computer modelling to study the colour change brought about by reflectance of the particles. Both organic carbon and dust particles have the ability to preferentially absorb light in the blue region of the spectrum. The absorption of blue light by these pollutants in turn gives the marble surface a brown hue.

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http://www.thehindu.com/sci-tech/energy-and-environment/taj-the-pollutants-causing-discolouration-identified/article6701369.ece