Characteristics and Recognition Thresholds of Environmental Odours in Ontario

Although detection threshold is the enforcement standard for environmental odour in Ontario, enforcement of odour limits is often driven by complaints, which occur when odours are typically present in concentrations above the detection threshold. As a result, a variety of other parameters, such as recognition threshold, hedonic tone, and descriptive odour characteristics that impact the likelihood of complaint, can be used when evaluating odour. While more subjective than a detection threshold, these parameters can provide additional context to an odour, and are used in some jurisdictions to modify odour limits.This study looks at over 1400 odour samples analyzed at the Pinchin Environmental Ltd. odour laboratory over the course of three years, starting with data collected in 2008. All samples were analyzed for their respective detection and recognition thresholds, hedonic tone, and were assigned subjective odour descriptors by an 8-member calibrated odour panel. Since environmental odour work in Canada is frequently spurred by public complaint, this study investigates whether odours with a certain character or hedonic tone can be more easily recognized than others, and whether the recognizable characteristics of environmental odour samples in a laboratory setting are significantly different from “Low Odour” samples, at each sample's recognition threshold.Analysis shows that, when given eight standard descriptors to choose from, most environmental odour samples analyzed in this study are characterized as “Chemical”, “Offensive”, or “Earthy”. Since many odour sampling projects in Ontario are complaints-driven, the results would seem to indicate that these three characteristics are most often associated with complaints. Although samples assigned one of the three primary descriptors do not have statistically different recognition thresholds, they do have different hedonic tones. This indicates that these odours can be recognized at similar concentrations, but the impact of that recognition, in terms of how it is described and the degree of unpleasantness of the odour, is different. The most unpleasant samples analyzed were shown to have a statistically lower average recognition concentration threshold than other samples analyzed. While there is no significant difference between the recognition threshold for “Low Odour” samples and recognition thresholds for other environmental samples, each group is generally assigned different hedonic tone values and descriptors.This study is intended as a contextual baseline for environmental odour analysis, by providing a larger picture of how odours are perceived, and which types of odours may lead to complaints. This information can then be used as a comparison tool for facilities undertaking smaller scale assessment and abatement projects. This research will be of benefit to facility operators dealing with odour issues and complaints, since certain compounds may be associated with particular characteristics and thus certain degrees of perceived pleasantness or unpleasantness. Additional research is required to determine which of a pool of more specific odour descriptors are considered the most unpleasant, and whether certain odours or hedonic tone values can be associated with specific industries and sources.