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 ch ronic effects of ambient particles on respiratory health. Because fine particles are capable of penetrating deeply into the respiratory syst em, most of the health studies have focused on the respirable portion or the particle size spectrum. Previous studies to examine exposure/re sponse 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 co llected particles may be difficult to redisperse. In addition, the che mical and physical characteristics of ambient particles may change upo n resuspension. We have developed a new technique that enables us to i ncrease the concentration of ambient particles to levels about 10 time s higher (or more, if desirable) than their ambient values and supply them to an exposure chamber. Ambient aerosol containing particles in t he size range 0.1-2.5 mu m can be concentrated using a series of two s lit-nozzle virtual impactors. The intake flow rates are 1 m(3)/min and 200 L/min in the first and second virtual impacters, respectively. Th e 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 a re maintained airborne, they can be supplied to a human or animal expo sure chamber for conduction of exposure studies. The supply flow rate in the prototype concentrator is 40 L/min. Higher flow rates can be ac hieved by using more than one such system in parallel.