The analytical difficulties in odour measurements are related to the well known complexity of our olfactory sensory perception. Still the importance of such an analysis in environmental pollution is, in certain fields, of primary importance, and there is a strong need of instrumental analytical technologies to quantify the odour to define objective odour policy criteria. There is a lack in the actual legislation in specific odour control procedure and this paper discusses about the possibility of using instrumental analysis, in conjunction with sensorial analysis, to characterize odour emissions in order to detect malfunctions in the facilities and to prevent air pollution and olfactive nuisance in the environment. We present here results from a study, performed during environmental odour episodes, in the area surrounding a composting plant and a MSW landfill. Odour episodes were perceived as far as 3 km downwind, where ambient air has been sampled. Results seem to suggest that the main odour sources, responsible for this episode, were related to the bio-oxidation building area. The pattern of organic compounds emitted from the odour abatement systems and from the close-by landfill appears statistically different from ambient air samples and were well separated by statistical multivariate analysis.