The goals of the experiments described herein involve determining in real time the size, concentration enrichment, and chemical composition of coarse-mode (> 2.5 μm) and fine-mode (< 2.5 μm) particles within the nonconcentrated and concentrated flows of a coarse particle concentrator used for human exposure studies. The coarse particle concentrator was intended to concentrate ambient particles in the PM_10-2.5 size range before sending them into a human exposure chamber. The aerodynamic size and chemical composition of particles in the upstream and downstream flows of the concentrator were monitored with an aerosol time-of-flight mass spectrometer (ATOFMS) for fixed time intervals over the course of three days. Based on the ATOFMS results, it was found that there was no change in the composition of the ten major particle types observed in the upstream and downstream flows of the concentrator under normal operating conditions. Furthermore, no new particle types were detected downstream that were not detected upstream of the concentrator. A characterization of the aerosol chemical composition and its dependence on sampling conditions is also discussed. Aerosol size distributions were measured with three aerodynamic particle-sizing (APS) instruments sampling simultaneously from different regions of the concentrator. The APS size distributions were used to scale ATOFMS data and measure the ambient concentration factors for the coarse particle concentrator and the exposure chamber. The average concentration factor (ratio of inlet number concentration to the outlet number concentration) for the particle concentrator was 60 ± 17 for the 2.5-7.2 μm size range before dilution and transport to the exposure chamber. It was observed that not only were coarse particles being concentrated but fine (< 2.5 μm) particles were being concentrated as well, with concentration factors ranging from 2-46 for aerodynamic particle sizes from 0.54-2.5 μm.