Theory and methods for odor evaluation

The typical study of the sense of smell is concerned with the effects of a single odor substance. Most of our knowledge therefore applies to pure substances and not complex gas mixtures 27,42,66. In real life, however, most odors are complex mixtures of various components in rather low concentrations. Although much is still unknown about the functioning of the olfactory system, the knowledge available gives an impressive picture of its capacity 22. For example, the ability to discriminate among odorous compounds is enormous even in the ever present odorous environment zs. Further, the sense can handle a wide range of stimulus concentrations and can often detect odor substances at the ppb level ~. On the other hand, the sense of smell is easily fatigued by continuous and constant odor exposure, though it recovers fast on the termination of exposure 38,42. The development of optimal methods for sensory odor evaluation using human observers presents both a challenge and a promise, regardless of whether the odor system is used as a measurement tool or as an indicator of environmental pollution. In the following, theories and methods for odor evaluation are discussed. Examples are given from laboratory as well as field research. Needless to say there is not much difference in the methodological requirements of basic and applied research.