It is often said that odor measurement is subjective. This statement comes certainly because odor measurements are based on human odor panels that sniff the air to determine the presence of odor.
It is likely also due to the variation in people’s sensitivity to odor or personal appreciation of different odors.
Odor measurement is, as a matter of fact, a dose-response relationship evaluation of an odorant substance. The dose-response relationships are commonly used in pharmacology, toxicology, biology and medical science. No one would think that these sciences are subjective. Olfactometry (odor measurement) is based on the same sound science.
The dose-response relationship, or exposure-response relationship, describes the change in effect on an organism caused by differing levels of exposure (or doses) to a stressor (usually a chemical) after a certain exposure time. This may apply to individuals (eg: a small amount has no observable effect, a large amount is fatal), or to populations (eg: how many people or organisms are affected at different levels of exposure). (Source: Wikipedia).
Dose response curve from an olfacomtetric analysis
In the case of odor measurement:
- the change in effect on an organism is the odor perception
- the differing levels of exposure (or doses) are the dilutions of odor
- the stressor is the odor
- the population sample is the odor panel.
An olfactometric analysis is an analytical test of odor quantification or measurement of the odor concentration (according to established protocols). The goal of an olfactometric analysis is to determine the odor perception threshold. By definition, the perception threshold is when 50% of the population detects an odor because of the presence of odorant chemical compounds. The Odor unit, is by definition, 1 o.u./m3, the odor perceived (but not necessarily recognized) by 50% of a panel (1 o.u./m3 corresponds to the detection threshold). The Odor concentration (number of odor units) represent the number of dilutions (with odorless air) of the gas mixture required to obtain 1 o.u./m3. The greater the number, the more “odorous” the sample is.
State of the art olfactometry will use panels that have been tested and selected according to the EN13725 standard and certified olfactometer operating in specific controlled conditions. This standard has been proven to provide reliable reproducible results.
It is absolutely valid to consider the odors subjective in terms of the appreciation of their quality. This belongs to the taste and experiences of each individual. On the other hand, the odor quantification is an objective method based on scientific fundamentals eliminating all the subjectivity related to odor perception.
Further readings:Get the white paper: Metrology of Odors – Olfactometry vs. Chemical Analysis. Which one will give you the most relevant information for your budget? Should you go for chemical analysis, olfactometric analysis or both?