A high-volume spray aerosol generator capable of producing small droplets for low-pressure applications, hereafter named filter expansion aerosol generator (FEAG), is described and characterized. The potential applications of this spray generator are thin film deposition, aerosol etching, and ultrafine particle preparation by spray pyrolysis at reduced pressure. The FEAG is mainly composed of a pneumatic nozzle for dispersing liquid, a porous glass filter with 80 mm diameter, and a vacuum pump (600 1 min(-1)). The liquid Row rate through the filter was 3 cm(3) cm(-2) h(-1). The mean droplet size was estimated to be 2.1 mu m with a geometric standard deviation 1.76. In principle, this generator can be scaled up by increasing vacuum pump capacity and filter area.