Uncertainty of olfactometry measurements caused by sampling issues
Abstract:Odor measurements by dynamic olfactometry can be affected by odor background from sampling bags and by interactions of odorants with the bag material during sample storage. In this study, we aimed to assess the odor background from new and pre-flushed bags, potential background from field exposure (assessed from field blanks), and the impact of overnight sample storage. These assessments were conducted for both Tedlar® and Nalophan® bags, focusing on odors emitted from municipal wastewater treatment (sewage, aeration basins and sludge), livestock manure and coffee. Olfactometry analyses were conducted on Odile 2510 and followed the EN13725 standard.
The odor background from new non-flushed Tedlar and Nalophan bags (in which odorless air was stored for 24 h) was as high as 75–317 odor units per cubic meter of air (OU/m3) for Tedlar or 36–43 OU/m3 for Nalophan. For pre-flushed bags, the background was reduced to 25–92 OU/m3 (Tedlar) or 19–26 OU/m3(Nalophan). It suggests that although modern olfactometers allow very low dilution ratios, in practice, special caution is needed before considering values in the range of several to a few tens of OU/m3. Potential background from field exposure as assessed from field blanks was substantial in Tedlar (in the range of several hundreds OU/m3 after 4 h exposure in a calves' barn or a wastewater treatment plant, respectively) and was negligible in Nalophan bags.
The effect of sample storage was found to vary among the different odor sources and the two types of bags. Storage had the greatest impact on coffee odor (both in Tedlar and Nalophan bags) with average losses by factors of 4–5, and for manure odor in Tedlar bags with an average loss by factor of around ∼6. Losses of sewage odor were by factor of ∼2 in Tedlar but odor was increased by factors of ∼3 in Nalophan bags.
The performance of the jury was monitored within actual sessions along the study period and was found in compliance with the EN 13725. The panel's response to n-butanol was found to be fairly stable (geometric mean of 33.3 ppb) suggesting that the effect of storage reported in this study can only be partly attributed to the uncertainty associated with the variation among panelists.
For practical reasons and before more advanced sampling methodologies are available, it is recommended that local/national standards will include more information about the potential impact of odor backgrounds and sample storage, such that labs will be able to provide a better assessment of the potential uncertainties associated with odor values and dispersion models that are based on these measured values.
Document Type: Research Article
Publication date: 2012-01-01
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