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The optical properties of combustion-generated soot, crucial information for quantitative soot emission diagnostics 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 experiment, and quantified using extractive methods coupled with scanning and transmission electron microscopy in conjunction with a detailed uncertainty analysis. The absorption component of the total measured extinction was isolated by calculating the expected scattering contribution, according to the Rayleigh–Debye–Gans approximation for polydisperse 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 …