Abstract: This invention is embodied in an apparatus for assessing the effects of controlled amounts of well-characterized ionic or other particles on the reliability of electronic components. The chamber includes a high efficiency filter that purifies the input air and a recirculating system which ensures substantially laminar, constant velocity air flow, controllable humidity, and steady state conditions throughout at least a portion of the chamber. Particles are introduced into the chamber from a particle generator through a series of output ports that ensure a uniform concentration of particles throughout at least a portion of the chamber. Substantially constant conditions are achieved by constantly introducing new particles into the chamber, withdrawing a continuous flow of particle-laden air from the chamber, removing essentially all the particles from the particle-laden air withdrawn from the chamber and introducing a continuous flow of filtered air into the chamber.