Research Program Area: Health & Exposure
Topic Areas: Toxic Air Contaminants
Particles in the atmosphere are a complex and heterogeneous mixture that have been difficult to reproduce in the laboratory. As a result, scientists have not been able to conduct toxicological and clinical experiments that replicate realistic conditions in the environment. Investigators have typically generated synthetic atmospheres that differ in significant ways from the true environment. This has made it difficult to address unanswered questions about the true nature and mechanisms of action of atmospheric particles (PM) on human health.
To study the health effect of PM in a realistic setting we designed, built and evaluated a Versatile Aerosol Concentration System (VACES) for testing the toxicological significance of concentrated atmospheric aerosols in animals. The system has been designed for conducting animal exposure studies, but it can be readily scaled-up for human exposures. This report describes the development and bench-testing of a VACES capable of simultaneously concentrating ambient particles of the coarse, fine and ultrafine size fractions for conducting in vivo and in vitro exposure studies to "real" ambient aerosols over a wide dynamic range of concentrations. The VACES consists of three parallel sampling lines (concentrators), each operating at an intake flow rate of 110 LPM. Coarse particles are concentrated using a single round nozzle virtual impactor. Concentration enrichment of PM2.5 and ultrafine particles is accomplished by first drawing air samples through two parallel lines, having 2.5 and 0.18 µm cutpoint pre-impactors, respectively, to remove particles larger than these sizes from the air sample. Both of the smaller PM fractions are drawn through a saturation-condensation system that grows particles to 2-3 mm droplets, which aresubsequently concentrated by virtual impaction. A diffusion dryer is used in the fine and ultrafine concentrators to remove excess vapor and return the concentrated particles to their original size, prior to supplying them for in vivo exposures. The VACES can also provide highly concentrated liquid suspensions of particles of these three modes for in vitro toxicity studies. This is accomplished by connecting the concentrated output (minor) flows of each of the VACES parallel concentrators to a liquid impinger (BioSampler), used in a modified configuration, to collect particles under near-ambient pressure.
Detailed laboratory characterization of the individual components of the VACES are presented in this paper, including evaluation of its ability to preserve particle mass, number, and chemical species during the concentration enrichment process. The experimental characterization of the VACES demonstrated that concentration enrichment is accomplished with very high efficiency, minimal particle losses and without any dependence on particle size or chemical composition.
For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753
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