The white marble domes of the Taj Mahal, an iconic image of India attracting millions of visitors every year, have lost their color several times over the last decades. The discoloration is linked with poor air quality; however, the specific components responsible have not been identified, so far.

M. H. Bergin, Georgia Institute of Technology, Atlanta, GA, USA, S. N. Tripathi, Indian Institute of Technology, Kanpur, India, and colleagues have collected ambient particulate matter (PM) samples over a one-year period. They found high concentrations of light absorbing particles including black carbon (BC), light absorbing organic carbon (brown carbon, BrC), and dust to be responsible for the surface discoloration of the Taj Mahal. BC and BrC result from the combustion of fossil fuels and biomass. Both organic carbon and dust have the potential to preferentially absorb solar light in the blue region of the spectrum. This can give the atmosphere a brown tone and has thus been called the Atmospheric Brown Cloud.

The team developed a measurement/modeling approach which allows surface color changes to be estimated based on the relative amounts of light absorbing particles deposited to surfaces. This can be used to develop future control strategies to prevent the discoloration of the environment by particle deposition.

• The Discoloration of the Taj Mahal due to Particulate Carbon and Dust Deposition,
  M. H. Bergin, S. N. Tripathi, J. Jai Devi, T. Gupta, M. Mckenzie, K. S. Rana, M. M. Shafer, Ana M. Villalobos, J. J. Schauer,
  Environm. Sci. Technol. 2014.
  DOI: 10.1021/es504005q