Ejector devices and systems are provided, that entrain ambient air within a primary stream of pressurized air, for use in a variety of applications including aircraft, buildings and other stationary structures. The ejector draws ambient air through an air treatment means such as a filter before its entrainment within the primary stream. The combined streams are then delivered to a ventilation system, an air curtain or other suitable recipient of treated, thermally conditioned air. The systems include diffusers, air curtain systems and variable air volume ventilation systems for aircraft and other vehicles.