Abstract: A method and apparatus for dispersing a substance, in particular a fragrant or disinfectant substance, into a volume of air comprises a first step of circulating a volume of air inside a conduit and a second step of liberating the substance into the conduit. Circulation of the volume of air ensures ventilation for example of a vehicle, a restaurant, a cinema, or furthermore, a hospital. The substance liberated into the conduit is dispersed in the volume of air by forced convection and leads to a perfumed environment or to air containing an active disinfectant principle. A cylinder is positioned outside the conduit containing the substance to be dispersed and a compressed propellant gas, and the propellant gas is expanded so as to inject the substance into the conduit.