Development and Laboratory Performance Evaluation of a Personal Cascade Impactor

Abstract

This paper presents the design and laboratory evaluation of a personal cascade impactor. The system is compact, lightweight, and uses a single battery-operated sampling pump. It operates at a flow rate of 5 L/min and consists of four impaction stages, each equipped with slit-shaped acceleration nozzles, and a backup filter. The impactor was calibrated using polydisperse particles. The 50% cut points of the four stages were 9.6, 2.6, 1.0, and 0.5 μm, respectively. The backup filter is placed downstream of the fourth stage and is used to collect the particles with an aerodynamic diameter smaller than 0.5 μm (d_p < 0.5 μm). The major feature of this novel sampler is its ability not only to fractionate the particles with an aerodynamic diameter smaller than 10 μm to the various size fractions, but also to collect them onto relatively small polyurethane foam substrates without using adhesives. Although the impaction substrates are not coated with adhesives such as grease or mineral oil, particle bounce and re-entrainment losses were found to be insignificant. Interstage losses of particles smaller than 0.5 μm were less than 10%; for fine particles, less than 5%; and for coarse particles, less than 12%. The pressure drop across the four stages and the backup filter were 0.015 kPa (0.153 cm H₂O), 0.025 kPa (0.255 cm H₂O), 0.274 kPa (2.794 cm H₂O), 0.323 kPa (3.294 cm H₂O), and 0.370 kPa (3.773 cm H₂O), respectively. Particles can be easily recovered from the foam substrates using aqueous extraction.