Overview of aerosol growth by coagulation and sintering showing the evolution of primary particle (PP) diameter, dp (blue solid line), and agglomerate collision diameter, dc (blue dashed line), with a typical temperature profile (red dash-dot line) (127) along with the relative magnitude of the characteristic times of coagulation, τc, and sintering, τs. The evolution can be divided into three stages: full coalescence (τc >> γs), aggregation (τc ~ τs), and agglomeration (τc << τs); the first and second stages determine the PP and average aggregate sizes, whereas the second and third stages determine the agglomerate size (64). The length of the middle stage (τc ~ τs) determines if agglomerates of aggregates (top, upper path) or of spherical particles (top, lower path) are formed---in other words, the extent of aggregate formation and hard bonding between PPs (dcH/dpH). For dcH/dpH → 1, few, if any, aggregates are formed.