DEVELOPMENT AND EVALUATION OF A PROTOTYPE AMBIENT PARTICLE CONCENTRATOR FOR INHALATION EXPOSURE STUDIES

A number of studies have underlined the importance of the acute and chronic effects of ambient particles on respiratory health. Because fine particles are capable of penetrating deeply into the respiratory system, most of the health studies have focused on the respirable portion or the particle size spectrum. Previous studies to examine exposure/response relationships between particle exposure and adverse respiratory effects have been based on artificial preparations, or collected and resuspended ambient particles, rather than the natural material found in ambient air. Artificial particles may not be representative, and collected particles may be difficult to redisperse. In addition, the chemical and physical characteristics of ambient particles may change upon resuspension. We have developed a new technique that enables us to increase the concentration of ambient particles to levels about 10 times higher (or more, if desirable) than their ambient values and supply them to an exposure chamber. Ambient aerosol containing particles in the size range 0.1-2.5 mu m can be concentrated using a series of two slit-nozzle virtual impactors. The intake flow rates are 1 m(3)/min and 200 L/min in the first and second virtual impacters, respectively. The virtual impacters were characterized in terms of their cutpoints and interstage losses using artificial monodisperse fluorescent aerosols as well as indoor ambient aerosols. Since the concentrated particles are maintained airborne, they can be supplied to a human or animal exposure chamber for conduction of exposure studies. The supply flow rate in the prototype concentrator is 40 L/min. Higher flow rates can be achieved by using more than one such system in parallel.