Dense particles, such as the primary particles in aerosol agglomerates, are formed by coagulation with rapid coalescence, or by condensation-like growth. This latter mechanism is explored in a new model. It uses the discrete-sectional model to describe the evolution of the particle mass distribution. In addition, new equations are used to describe the formation of primary particles. Primary particles are born when a new particle is formed above a critical size D m e l t . Particles smaller than D m e l t are assumed to be liquid-like, sintering rapidly in the available time. Changes in the final primary particle size D p can be attributed to growth from small particle deposition. This growth increases as the monomer source rate decreases. For conditions representative of TiO 2 formation from chloride in a tube reactor, D p /D m e l t ranges from 1.5 to 3. When D m e l t decreases, as would be expected if temperature decreases, D p /D m e l t increases. The result is that sintering models.