Aerosol Dynamics Relation to Characterization

Aerosol characterization as discussed in this chapter provides a snapshot of the aerosol al a given position and time. The snapshot gives information on panicle size and chemical properties that determine many of the effects of aerosols, both desirable and undesirable. However, the size distribution and chemical properties usually change with time and position in industrial process gases or in the atmosphere. 

Consider a small volume of gas and associated particles and follow its motion through the system—that is. the atmosphere or an industrial process. The physical and chemical processes shaping the size distribution are summarized in Fig. 1.7. The change in (u, r, /) with time can be expressed as the sum of two terms  

The first term on the right represents processes occurring inside the element including gas-to-particle conversion and coagulation. The second term represents transport across 

1 Plot (he number of molecules as a function of particle size for silica nanopartides dp 50 nm). On the same (igure, plot the fraction of the molecules that appear in the surface of the particles. This will require certain assumptions that you should state. 

2 Derive an expression for the rate at which the particles of a polydisperse aerosol settle on a horizontal plate from a stagnant gas. Dimensions arc number per unit time per unit area. Assume that Stokes law holds for the terminal settling velocity, and express your answer in terms of the appropriate moments. 

---