Characterization of a Microscale Cascade Impactor

Although a cascade impactor is widely used for bioaerosol sampling and separation, the conventional system has some shortcomings when it is applied for the portable device. In the present study, a microscale cascade impactor system was developed using a soft lithography process to provide good portability and cost efficiency. The system described here included three impaction stages, and a rectangular-shaped jet nozzle was employed with a 0.5 L/min airflow rate. The collection efficiency of each stage was evaluated using polystyrene latex (PSL) (0.2-2.5 mu m) and ammonium sulfate (10-700 nm) particles. The 50% cutpoints of each stage were numerically calculated to be 1.06, 0.55, and 0.26 mu m, and the experimental values were found to be 1.19, 0.51, and 0.27 mu m, respectively. The bounce and re-entrainment in the impaction zone were reduced by spin-coating of silicon oil onto the microchannel surface. The overall particle losses were less than 10% for the 0.2-2.5 mu m particles and 9%-12% for the 0.05-0.20 mu m particles.