Characterization of the University of Toronto Concentrated Aerosol Particle Exposure Facility (CAPEF)—Effects on Fine and Ultrafine Nonrefractory Aerosol Composition

摘要

Virtual impactor-based particle concentrators have been developed to enable the study of biological mechanisms and dose-response relationships of particulate matter (PM) inhalation. The Concentrated Aerosol Particle Exposure Facility (CAPEF) at the University of Toronto houses the Harvard School of Public Health designed coarse, fine, and quasi-ultrafine particle concentrators for such studies. Characterization of the concentration of the non-refractory components of ambient particles was carried out in the winter of 2010. The fine concentrator shows higher mass concentration factors for ambient sulfate than for semi-volatile components, as measured using an Aerodyne aerosol mass spectrometer (AMS). The change in composition is based on the relative size distributions of particulate sulfate, which, compared to particulate organic and nitrate, is more dominant in larger particles more efficiently concentrated due to the physical characteristics of the virtual impactors. The ultrafine concentrator, which requires aqueous condensational growth of particles prior to concentration, shows a large enhancement in organic mass both for ambient particles and for laboratory-generated ammonium sulfate and ammonium nitrate particles added to filtered outdoor air. As suggested previously, changes in the organic mass spectrum and size distributions are consistent with addition of organic mass through reactions of water-soluble volatile organic compounds. Coagulation of particles or droplet coalescence may also account for some of the observed increase in organic mass and nitrate may be lost due to volatilization. While such effects are unlikely to affect refractory species, increased attention should be given to the effect of condensational growth on the composition of concentrated ultrafine particles.