formation of fines in a fluidized catalytic cracker unit (FCCU) due to catalyst attrition and fracture is a major source of catalyst loss. in addition to the generation of fine particles, a significant amount of aerosols have been identified in the stack emission of FCCUs. To determine the source of these aerosols, samples of fresh and equilibrium (c-cat) type catalysts were heated up to 600 degreesC and mixed with cold samples, simulating the thermal shock and particle fracture, which occurs inside an FCCU when catalyst is added. The thermal shock in the experiments produced fine particles and aerosols, which were captured on filters and analyzed using scanning electron microscopy (SEM) imaging and atomic absorption tests. It was found that significant quantities of metal rich aerosols were generated by the thermal shock. This production of fine particles and aerosols is a new phenomenon that can help explain excessive catalyst emissions from operating FCCUs. (C) 2003 Elsevier B.V. All rights reserved.