Abstract: A system capable of detecting low-level releases of bio-agents and other harmful substances contained in air concentrates and recycles exhaust air from a collector in order to entrain and retain more particles from an aerosol release event. The system ensures that particles that were not initially entrained or subsequently retained will have successive opportunities to be entrained within the collection solution. The system also optionally utilizes concentrators in series and a collector to ensure that the particle content of air entering the collector is maximized.