 this paper presents the development and evaluation of an ambient particle concentrator for conducting animal inhalation exposure studies . 
 the system utilizes the principle of virtual impactors to concentrate ambient particles in the size range 0.1 - 2.5 microns ( aerodynamic diameter ; dp ) by drawing them through a series of three virtual impactors . 
 each impactor contains the majority of ambient fine mass ( dp < 2.5 microns aerodynamic diameter ) in a bleed flow ( minor flow ) that is 20% of the total flow entering the virtual impactor . 
 the virtual impactors have been characterized using indoor air samples as test aerosols . 
 fine mass and sulfate concentrations at the outlet of the concentrating system were compared to the ambient fine mass and sulfate levels , which were determined using harvard - marple impactors . in each of the stages , 
 particle concentration was increased by a factor of approximately 3 . 
 thus , an overall concentration factor of about 25 - 30 was achieved . 
 the main goal of this study was to demonstrate the feasibility of conducting animal exposures using the newly developed ambient fine particle concentrator.imagesfigure 1.figure 2.figure 3.figure 4.figure 5.figure 6 . 
Images