Development of a High Volume Cascade Impactor for Toxicological and Chemical Characterization Studies

This paper presents the design and development of a compact high volume cascade impactor (HVCI). The HVCI operates at a  ow rate of 900 l/min and consists of 4 impaction stages equipped with circular slit-shaped acceleration nozzles and a backup Ž lter. The backup Ž lter is placed downstream of the fourth stage and is used to collect the ultraŽ ne particles (dp < 0.1 1m). The major feature of this novel sampler is its ability to collect relatively large amounts of particles (mg–g levels) onto relatively small polyurethane foam substrates without using adhesives. As previously reported, the capacity of the impaction substrate is 2.15 g of collected particles per cm of foam. Although the impaction substrates are not coated with adhesives such as grease or mineral oil, particle bounce and re-entrainment losses were found not to be signiŽ cant. Particles can be easily recovered from the foam substrates using aqueous extraction. The impactor was calibrated using polydisperse particles. The 50% cutpoints of the 4 stages were 9.90, 2.46, 1.0, and 0.1 1m, respectively. Interstage losses of ultraŽ ne and Ž ne particles were <10% and for coarse particleswere<20%. The pressure drop across the 4 stages and the backup Ž lter were 0.25, 0.75, 1.25, 19.9, and 3.3 kPa, respectively.