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One Odour Unit-Precisely How Can an Odour Unit be Measured

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Abstract:

Odour is considered a nuisance in most jurisdictions in Canada, Australia and the United States. Some provinces and states have regulations for odour. For example in Canada the Ontario Ministry of the Environment (MOE) has a target odour concentration of one (1) odour unit (ou) at the property line or at any sensitive receptor. This is based on either measurement at potential odour sources and dispersion modeling to predict the off site odour concentrations or just ambient air measurements. In Queensland, Australia the requirement is even more stringent, requiring 0.5 ou for tall stacks or 2.5 ou for short stacks. How precisely can we measure or predict odour units? Is it possible to measure or predict 0.5 ou or 1.0 ou? One odour (ou) unit might very easily be measured as 10 ou and will depend on the methodology used for collection of the samples, their evaluation or the selection of potential odour sources. It is not possible to be exact with requirements such as 1 ou or 2.5 ou due to several factors such as: different, not necessary correct methodology used for odour sampling, especially for hot, humid sources or even at area sources, uncertainty in sampling for fugitive sources which might contribute significantly to off site odours. On the other hand, the emission rates are based only on a one time snap shot instead of continuous monitoring. Finally, the dispersion modelling itself has errors, as well. Therefore, for the same facility the off-site odour concentration might be 1 odour unit (ou) ,but could very easily be 10 odour units or higher. This depends who assesses that particular facility and how the samples are collected or analyzed. Currently, there is too much emphasis on analysis of already collected odour samples but not enough attention on sample collection methodology or selection of the sources.

This paper will introduce several studies showing significant differences in results when different sampling approaches are used. This paper will also introduce the results for the same sources assessed at the same time using different methodologies used for collection of samples from point sources, area sources and at ambient locations. This paper shows a significant difference between the final results when the dynamic dilution technique is used for collection of odour samples versus results when the lung technique is used for the collection of odour samples from the same point sources. Also in this paper, the final results are introduced for samples collected at the same area sources using two different techniques: flux chamber technique and wind tunnel technique.

The ambient results are also introduced when different techniques were used for assessing ambient odour levels.

This paper will also emphasize the need for proper sampling especially for hot, humid sources and area sources. The losses of odour might be significant if proper methodology is not used. The important question is what is the proper methodology? Until a specific method for sampling, using step-by-step methods similar to sampling other compounds such as volatile organic compounds or particulates is used by the same consultants, one odour unit does not have any value in the real world. Therefore, talking about 1 odour unit or 5 odour units is unrealistic unless a proper sampling methodology is put in place and is followed by everybody around the world.

Keywords: Nasal Ranger; Odour; odour evaluation; odour sampling; olfactometry

Document Type: Research Article

DOI: http://dx.doi.org/10.2175/193864710802768244

Publication date: January 1, 2010

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  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

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