Infrared extinction spectra in the 2-12 μm region have been obtained for smokes of wood, polystyrene foam, polyvinyl chloride and kerosene.
Spectra were found to depend on smoke generating condition (smouldering of flaming) rather than on the sort of combustibles. In the 2-5 μm region, extinction coefficients for white smokes from smouldering solid combustibles were inversely proportional to the cube or fourth power of wavelength, while those for black smokes by flaming combustion were approximately proportional to the inverse of wavelength. In the 5-12 μm region, the extinction characteristics showed some irregularities probably due to selective absorption by water vapour and other gaseous combustion products.
Experimental results with smouldering smokes were compared to calculated extinction characteristics based on the Mie theory to estimate smoke particle sizes. These were, in diameter, 1.2-1.3 μm for wood, 0.6-0.7 μm for polystyrene foam, and 0.7-0.8 μm for polyvinyl chloride, and were in good agreement with values formerly obtained by sedimentation method.