OPTICAL-CROSS-SECTIONS OF SOOT AGGLOMERATES - THE MODEL OF THE VIRTUAL REFRACTIVE-INDEX AND FIRST-ORDER MULTIPLE-SCATTERING

A new technique for the calculation of the optical properties of agglo merated spherical primary particles is presented. By means of the so-c alled virtual refractive index, the multiple scattering within the agg lomerate is described by a modified Mie solution, thus avoiding restri ctions with respect to the primary particle size. An additional benefi t of the method is the small numerical expense required, permitting pr actical use for complex agglomerate structures such as real combustion aerosols. Utilizing this method, attention is focused on the calculat ion of the extinction cross-section of real combustion aerosols in ord er to discuss the results of multiple-wavelength extinction measuremen ts within combustion systems. It is found that approximately the prima ry particle diameter is determined. Furthermore, the error that occurs can be avoided by means of the method presented without a detailed kn owledge of the agglomerate size. Thus, the present work eliminates som e current uncertainties inherent in optical combustion aerosol charact erization.