The invention relates to a method and a device for disinfecting the air of an air flow (2) inside an air supply duct (1) with a nontoxic disinfectant. The disinfectant is sprayed and injected in the injection direction (31) by means of at least one injection nozzle (30) of an injection device (3), the injection direction (31) approximately corresponding to the direction of the air flow (2). The injection in the region located after a contraction (12) in the duct and the related flow acceleration enables an absorption of the particles on the inner walls (100) of the air supply duct (1), over the entire length of the air supply duct (1).
