Measurement and modeling of the multi-wavelength optical properties of uncoated flame-generated soot: Data from the BC2, BC3, BC3+ and BC4 studies

Optical properties of flame-generated black carbon (BC) containing soot particles were quantified at multiple wavelengths during the BC2, BC3, BC3+ and BC4 campaigns. The particles were produced using two different flames, either an ethylene premixed flame (sampled at multiple heights above the flame front) or a methane diffusion flame. Measurements were made both for size-selected nascent soot particles and for particles that were coated (with either dioctyl sebacate, sulfuric acid or secondary organic aerosol) and then thermally denuded to remove the coating. The coating + denuding process led to a collapse of the soot particles relative to their originally lacy, fractal-like morphology. Observed optical properties for methane diffusion flame-derived particles were similar to those from the ethylene premixed flame-derived particles when sampled 20 cm above the burner. In contrast, the optical properties of particles from the ethylene premixed flame sampled at only 5 cm above the surfa...