Abstract: A device for atomizing a liquid composition serves to treat a premises and equipment contained therein. The device is equipped with an atomizing nozzle including: a) a secondary duct (102) supplied with liquid and having an element (1) for effecting a first fractionation of the liquid inside an expansion chamber (2); b) a principle duct (101) flowed through by a gas stream and having an element (3) for effecting a second fractionation of the liquid, and; c) connecting element (5) for connecting a) and b). The nozzle can also be equipped with an ultrasonic resonator (21) and with a resonance chamber (22) situated in front of the discharge opening (4). Also disclosed is an atomizing method during which a first fractionation of the liquid is effected by suction through a first venturi (6), a second fractionation of the liquid is effected by suction into the gas stream while leaving a second venturi and, optionally, a third fractionation is effected by ultrasonic vibration.