FY 2002

Spectral dependence of visible light absorption by carbonaceous particles emitted from coal combustion

Bond, T.C.

Geophys. Res. Lett., 28(21), 4075–4078, doi: 10.1029/2001GL013652 (2001)

Optical characteristics of particles that absorb visible light are needed to model their effects on atmospheric radiation. Light absorption by particles emitted from low-technology coal combustion has exhibited a strong spectral dependence. I investigate various explanations for this phenomenon and conclude that a spectrally dependent imaginary refractive index is the most plausible. Following previous work on the structure of amorphous carbon, I propose that both the magnitude and spectral dependence of light absorption are controlled by the size of graphitic clusters within the material, and can be described using the optical band-gap theory. This hypothesis is an alternative to the current measurement divisions of light-absorbing "black carbon" and non-absorbing "organic carbon," and offers an explanation for preferential absorption at blue wavelengths that may extend to ultraviolet wavelengths.