Development and performance evaluation of a high-volume ultrafine particle concentrator for inhalation toxicological studies

This article presents the development and performance evaluation of a high-volume ultrafine particle concentrator. The ultrafine particle concentrator consists of several units, including a size-selective inlet; a condensational growth unit; a series of two virtual impactors (concentrators); a thermal size restoration device; an air cooler; and a size-selective outlet. Ambient ultrafine particles are condensationally grown to supermicrometer sizes and then are concentrated by a factor of 40 to 50 using a two-stage virtual impactor. Subsequently, ultrafine particle size distribution is restored, using a thermal method. The Harvard ultrafine concentrated ambient particle system (HUCAPS) delivers 58 lpm of concentrated aerosol that can be used for in vivo or in vitro inhalation toxicological studies. Overall, pressure drop through the system is only 2.2 kPa, which is adequately low for inhalation toxicological exposure tests. The performance of this system was evaluated using single-component artificial aerosols with a variety of physicochemical properties as well as ambient air. These experiments showed that for an optimum supersaturation ratio of 3.0, all ultrafine particles grow and get concentrated by about the same enrichment factor, regardless of their composition and surface properties.