Taj: the pollutants causing discoloration identified
Source: The Hindu, Date: December , 2014
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.