The submicron particles have a higher
probability of escaping conventional PECD than the other coarse
particulates. Once emitted in the environment, these submicron
particles exhibit lengthy atmospheric residence time and are
capable of deep pulmonary ingestion [33]. The formation of regular
spherical shape of submicron particles can be explained by
a mechanism of nucleation–condensation–coagulation after its
evaporation from its solid matrix under high temperature [34]. In
detail, the metals in ash matrix is firstly released and evaporated in
flame zone (more than 1100 C). In post-combustion zone, homogeneous
nucleation occurs and forms submicron particles due to
the reduction of temperature, and then heterogeneous condensation
of metal vapor onto submicron particles occurs in flue gas.