Odor frequency and odor annoyance. Part I: assessment of frequency, intensity and hedonic tone of environmental odors in the field

Objective Odors can be evaluated as being pleasant or unpleasant (hedonic tone), but this differentiation was not incorporated into environmental odor regulation. In order to study the hedonic-induced modification of dose–response associations for community odor annoyance a pertinent field study was conducted. This paper covers the first step, namely the development and validation of a standardized human observation strategy for the direct quantification of the frequency, intensity, and hedonic tone of environmental odors in the field. Methods Grids with equidistant observation points were located around six industrial odor sources, two with pleasant (sweets, rusk bakery), two with neutral (textile production, seed oil production), and two with unpleasant odor emissions (fat refinery, cast iron production). These points were visited by trained observers, screened for normal olfaction and reliable performance, in a systematic fashion for an observation time of 10 min duration. Exposure-related information from the observers in terms of frequency, intensity (six-point scale) and hedonic tone (nine-point scale) were compared to that of 1,456 residents using the same rating scales. Results Residents evaluated the industrial odors more intense and more unpleasant than the panelists. Furthermore, for the residents only negative relations between odor intensity and hedonic tone were found while for the observer pleasant odor became more pleasant with increasing intensity. Instead of three classes of industrial odors, namely pleasant, neutral and unpleasant, the responses allowed only for two odor classes, namely pleasant and not pleasant, the latter also covering the neutral category. Conclusions The developed methodology has been shown to yield valid information about odor exposure in the field. With regard to different application settings the discrepancies between external observers and affected residents are discussed in terms of different information processing strategies, namely stimulus-based (bottom-up) for the panel and memory-based and, thus, subject to cognitive bias for the residents (top-down). Parts of these findings were presented at the 15th Congress of the European Chemoreception Research Organization in Erlangen (2002), at the 43rd Congress of the German Society of Psychology in Berlin (2002), and at the at the 9th Meeting of the International Neurotoxicology Association in Dresden (2003).