IIT team tracks brown carbon’s effect on atmospheric warming

  • The effect of biomass burning in increasing atmospheric aerosols and in turn atmospheric warming through light absorption has been highlighted in a study by a team of researchers from the Indian Institute of Technology (IIT) Kanpur.
  • While the role of black carbon produced by biomass burning in increasing atmospheric warming has already been well established, this study highlights the lesser-known role of brown carbon.
  • Compared with earlier studies carried out in the U.S, absorption of light of 365 nanometre wavelength was found to be five times higher in Kanpur, which has a high biomass burning area.
  • Also, brown carbon accounts for about 30 % of light absorption in Kanpur.
  • What is seen in Kanpur can be generalised for the entire Indo-Gangetic Plain because the sources of aerosol remain the same throughout the region.
  • Though brown carbon is 10 times more than black carbon in terms of mass, the absorption capacity of black carbon is 50 times more than brown carbon.
  • As a result, up to about 70 per cent of light absorption during 24 hours is by black carbon. Brown carbon (when present independently) has nearly 15 per cent potential to warm the atmosphere by absorbing light.
  • Additionally, depending on the spectrum of light, the light absorption capacity of brown carbon is 15-30 per cent when present as a coating (shell) over a black carbon core. This is because the brown carbon coating behaves like a lens and focuses light towards the black carbon core.
  • The lensing (concentration of light on the core) is dependent on three parameters — ratio of the diameter of the shell to the diameter of the core, wavelength of light and the scattering or absorbing property of the coating.

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