An apparatus for dispersing in the air, in the vapor state, a substance which is in the liquid state at ambient temperature, and is contained in a storage container, the apparatus comprising: - a ventilation system comprising a duct (2, 4, 510) which opens out into the open air, and is configured to permit the passage of a flow of air into the duct; - at least one dispensing unit (8, 208) which is designed to be supplied with a liquid substance by the storage container, the dispensing unit comprising micro-ducts forming an outlet which is provided in the duct in order to constitute an area of evaporation of the substance therein; - at least one storage container (5, 106, 300, 400, 550) which contains the substance and is connected to the dispensing unit (8, 208), wherein the storage container (5, 300, 400, 550) has a discharge orifice which is connected to the dispensing unit, and - a heating unit (11, 211, 132) which is provided on or in the dispensing unit, such as to control a flow of the substance through the dispensing unit, the discharge orifice is oriented downwards when the apparatus is in a position of use, the dispensing unit being below the discharge orifice in the position of use, and in that the substance has a viscosity which is variable according to the temperature, the apparatus being characterized in that said viscosity is such that the substance can not flow through the micro-ducts of the dispensing unit at an ambient temperature lower than a first temperature, the heating unit being configured to heat the dispensing unit to a second temperature higher than the first temperature, such that a flow of the substance through the micro-ducts of the dispensing unit takes place by capillarity in the position of use. - a ventilation system comprising a duct (2, 4, 510) which opens out into the open air, and is configured to permit the passage of a flow of air into the duct; - at least one dispensing unit (8, 208) which is designed to be supplied with a liquid substance by the storage container, the dispensing unit comprising micro-ducts forming an outlet which is provided in the duct in order to constitute an area of evaporation of the substance therein; - at least one storage container (5, 106, 300, 400, 550) which contains the substance and is connected to the dispensing unit (8, 208), wherein the storage container (5, 300, 400, 550) has a discharge orifice which is connected to the dispensing unit, and - a heating unit (11, 211, 132) which is provided on or in the dispensing unit, such as to control a flow of the substance through the dispensing unit, the discharge orifice is oriented downwards when the apparatus is in a position of use, the dispensing unit being below the discharge orifice in the position of use, and in that the substance has a viscosity which is variable according to the temperature, the apparatus being characterized in that said viscosity is such that the substance can not flow through the micro-ducts of the dispensing unit at an ambient temperature lower than a first temperature, the heating unit being configured to heat the dispensing unit to a second temperature higher than the first temperature, such that a flow of the substance through the micro-ducts of the dispensing unit takes place by capillarity in the position of use.