Nonspherical aerosols can be encountered in postulated severe core damage accidents in nuclear reactors. Aerosol behavior equations are thus modified to account for the departure from spherical shapes by the introduction of a range of “shape factors,which are defined in terms of a specified characteristic dimension or property of the particles. These factors are then introduced into the aerosol behavior equation by modifying the normalized collision kernel. When gravitational effects alone are considered, the kernel is reduced to the gravitational collision kernel, and shape factors for individual particles are typically defined in terms of the dynamic shape factor, which is the ratio of the Stokes settling velocity to the aerodynamic settling velocity, and the collision shape factor (the ratio of the collision diameter to the volume equivalent diameter). Due to the inconsistencies and ambiguities of current usage, separate effects information on the collision shape factor is unavailable. A new shape factor, β, is introduced to clarify the definitions and relationships between the collision efficiencies of nonspherical and “equivalent” spherical particles. The shape factor, β, can be obtained from mechanistic considerations.