Spectrally resolved light absorption properties of cooled soot from a methane flame

摘要

The optical properties of combustion-generated soot, crucial information for quantitative soot emission di agnostics and for climate modeling, have been determined for the particular case of cooled soot from a methane flame. Optical extinction measurements were performed over a wavelength range of 450-750 nm using a novel diffuse-light, spectrally resolved line-of-sight attenuation experi ment, and quantified using extractive methods coupled with scanning and transmission electron microscopy in conjunc tion with a detailed uncertainty analysis. The absorption component of the total measured extinction was isolated by calculating the expected scattering contribution, accord ing to the Rayleigh-Debye-Gans approximation for poly-disperse fractal aggregates. In contrast to the large degree of scatter seen in data previously reported in the literature, a consistent trend of negligible variation of the soot absorp tion refractive index function E(m) with wavelength over the visible was observed (E(m) = 0.35 ± 0.03 at wave lengths of 450-750 nm). These new data are also cast in the form of dimensionless extinction, which is independent of the scatter correction, as well as mass absorption cross sec tion, which is independent of the mass density of soot and is commonly used by atmospheric modelers.