The objectives of this research are to develop experimental and theoretical procedures for online measurement and analysis of combustion, ammonium sulphate and nitrate particles formed in dry scrubbing processes, and silicon particles from the pyrolysis of silane. In silicon production, conditions are chosen to prevent cluster formation by operating at temperatures below where homogeneous nucleation occurs and with low concentration of nuclei. In the electron beam scrubbing processes, operating and installation costs are so expensive that short irradiation times at high doses are mandated. These conditions yield comparatively high water vapor concentrations will at least partially compensate, and a compact particle can be expected. The soot structures are extended chain-like structures. The specific research areas are: (1) the experimental measurement of the aerodynamic diameter of clusters and their correlation with primary particle size and fractal dimension; (2) the development of a coagulation model based on the Kaplan lattice approach; and (3) the diffusional charging of clusters and especially their role as a sink for ions.