Pumped Counter Flow Virtual Impactor: Numerical Evaluation

Counter Flow Virtual Impactors (CVI) of various designs are widely used in laboratory and field research, especially in ice and cloud droplet nuclei studies. A pumped CVI (PCVI), designed for ground operations, does not rely on aircraft flight or supplementary wind tunnel to produce the input flow. Here we present a quasi one dimensional model of a PCVI. The model, albeit a very simple, provides useful insights into the physical processes underling PCVI operation and explains limitations of the apparatus observed in experiments; for instance, why "perfect step function" transmission efficiency cannot be achieved for a PCVI.