State Homogeneous Nucleation Processes - Particle Growth

The large amount of seed presents a high-growth area from the outset of the operation. The initial presence of the seed avoids the issue of when to add it to prevent seed dissolution and homogeneous nucleation. Note that for this process, the size of the particles does not need to decrease, as steady-state particle size distribution is reached at the low but finite natural attrition rate achieved in the pump-around and agitation systems. 

The few observations of nucleation in the free troposphere are consistent with binary sulfuric acid-water nucleation. In the boundary layer a third nucleating component or a totally different nucleation mechanism is clearly needed. Gaydos et al. (2005) showed that ternary sulfuric acid-ammonia-water nucleation can explain the new particle formation events in the northeastern United States through the year. These authors were able to reproduce the presence or lack of nucleation in practically all the days both during summer and winter that they examined (Figure 11.16). Ion-induced nucleation is expected to make a small contribution to the major nucleation events in the boundary layer because it is probably limited by the availability of ions (Laakso et al. 2002). Homogeneous nucleation of iodine oxide is the most likely explanation for the rapid formation of particles in coastal areas (Hoffmann et al. 2001). It appears that different nucleation processes are responsible for new particle formation in different parts of the atmosphere. Sulfuric acid is a major component of the nucleation growth process in most cases. 

Major characteristics of homogeneous dispersions are the dynamic characters of their phase boundaries. There is a continues flux of material from the dissolved state into the solid state, and vice versa. The interfaces are dynamic and changing, with the process of ostwald ripening rapidly eliminating the smaller particles. Surface-active components may influence both the crystal growth and the nucleation. 

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