The determination, in terms of priorities, of actions to be conducted in order to lower the odour nuisances in the vicinity of an industrial plant, requires the establishment of a hierarchy of the different sources, and to the end, the evaluation of malodorous compounds emitted by the various types of structures. To answer this problem, it is necessary to develop, on one hand, very sensitive physicochemical analytical methods, with privileging the continuous analysis on the site, in order to evidence the nature of responsible malodorous compounds and the evolution of their emission with time and, one the other hand, protocols of specific air sampling, for determining the pollutant loads emitted into the atmosphere, specially from surface sources, The general methodology for sources characterisation is described and examples of applications in various types of Industrial plants are presented