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.
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)