**5. Summary**

412 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

(g) and droplet (d; drop). The droplet breaks when the We number is greater than 12. These

estimates can be validated by combining the observations and CFD simulations.

**Figure 4.** Interior surfaces of the PCVI instrument showing (upper panel) the particle deposition regions. These regions are indicated within CFD predicted velocity pathlines (bottom panel). See text

for details [3].

In this chapter, a technique that separates the cloud forming nuclei from the interstitial aerosols is briefly discussed. The technique is based on the inertia of the particle. Cloud forming nuclei are the residual particles of the droplets and ice crystals. These cloud hydrometeors have high inertia compared to the interstitial aerosols and therefore penetrate the counterflow region of the CVI to be sampled. Two types of CVI instruments are based on this technique: PCVI and ACVI. PCVI is generally used in the laboratory set-up where the particle velocity is achieved by pumping the input flow; whereas, in the ACVI, the particle velocity is generated by aircraft flight.

Transmission efficiency of the particles that are sampled can be theoretically calculated, and it was observed that as particle velocity and/or its diameter increases the efficiency also increases. Several artifacts of the cloud separation technique are described. They include particle losses and imperfect transmission efficiencies, flow turbulence effects on the droplet breakup and shattering, and possibility of scavenging of interstitial aerosols (this needs further investigation). However, many studies have quantified these artifacts and the cloud separation technique is now considered as a must have measurement platform for most of the laboratory and field studies.
