Odour episodes and environmental air quality are topics of worldwide concern, mainly due to the fact that industrial facilities are often located very close to inhabited areas. Several atmospheric pollutants, mainly volatile organic compounds (VOCs), are responsible for odour episodes of varying degrees of annoyance. A methodology based on the simultaneous application of social participation (by building databases of odour episodes and acquiring air samples), chemical control and the computation of back trajectories allows us to identify the origin of odour episodes. A validated analytical method, based on thermal desorption (TD) coupled with gas chromatography (GC) and mass spectrometry (MS), is used to identify and determine a wide range of VOCs that cause odour nuisance and affect air quality in outdoor air. Back-trajectory modelling is used to track the origin of the air mass responsible for the discomfort backwards in time, mainly to find possible VOC sources outside the urban area. The procedure combines, on one hand, an analytical approach based on the acquisition of samples, which requires the participation of the affected population (which means that social participation is used as a scientific tool), and on the other hand, a modelling approach. Three examples are described to illustrate the methodology.