Effects of physicochemical properties of ultrafine particles on the performance of an ultrafine particle concentrator

Abstract

Condensational growth of ultrafine particles under saturation conditions in conjunction with virtual impaction technology has been used recently as a method to concentrate ultrafine particles for conducting inhalation toxicological studies. The Harvard Ultrafine Concentrated Ambient Particle System (HUCAPS) was challenged with a variety of artificially generated aerosols of different chemistry, solubility, and hygroscopicity as well as by ambient-origin ultrafine particles. The system's ability to concentrate these different particles was evaluated for a wide range of saturation ratios. It was found that hygroscopic particles grow and are concentrated more efficiently than hydrophobic ones. The effect of aerosol-hygroscopicity and water solubility on the overall aerosol concentration enrichment factor diminishes with increasing saturation ratios. Results indicated that a saturation ratio higher than that predicted by theory, with a value of about 3, is needed to assure that all particles grow and are efficiently concentrated by the same enrichment factor, regardless of particle hygroscopicity and solubility. Under such an optimum saturation ratio, the performance of the HUCAPS was evaluated using ambient-origin ultrafine particles. The results show that the HUCAPS concentrates ambient ultrafine particles by a factor of 40-50 with a little size distortion. Its overall low-pressure drop (2.2 kPa) and its high concentration enrichment factor make the HUCAPS a versatile device suitable for in vitro and in vivo inhalation toxicological studies.