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An Odor Index Scale for Policy and Decision Making Using Ambient & Source Odor Concentrations

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The concept of odor strength (odor concentration) is often confusing. There is a need to better understand odor strength terminology and there is a need for odor strength bench marks.

Similar confusion or absence of bench marks once existed in the field of noise and sound measurement. However, now sound measurement values are fairly well understood with the universal use of the logarithm “decibel” sound measurement scale. The decibel, introduced in the early 1900's by researchers at Bell Laboratories, is a dimensionless unit based on the logarithm of the ratio of a measured quantity of sound to a reference quantity of sound.

In 1988, John E. Amore at the APCA 81st Annual Meeting (Amore and O'Neill, 1988) proposed an analogous value and scale to the “decibel” sound scale for expressing odor concentration. Furthermore, in Japan an “Odor Index” scale was introduced in 1995 (Ministry of the Environment, Japan, 1995).

The Odor Index value is dimensionless and universally defined as:

Odor Index = 10 × log10 (odor concentration)

Where odor concentration is determined using laboratory olfactometry or field olfactometry and reported as detection threshold (DT) or dilution-to-threshold (D/T), respectively. Note: odor concentration, a dimensionless dilution ratio, is commonly reported with the pseudo dimension of Odor Units (OU).

With standardization of odor testing methods in ASTM E679-04 (ASTM International, 2004) and EN13725:2003 (Committee for European Normalization, 2003) an Odor Index will provide a standard way to display and to report odor concentration values for policy and decision makers.

This paper will approach the odor index with the historical background and with a rational argument for adopting an odor index for common use.

Document Type: Research Article


Publication date: January 1, 2006

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