odor, how to measure?

Published on 21 September 2017Time to read: 4 minutes

As Aerox we offer our clients sustainable solutions for industrial odor emissions. Together with our customers we solve the nuisance resulting from these emissions. We therefore also regularly get questions about odor, what exactly this is and how you can measure it.

Measuring of smell

The objective measuring of odor is not easy. odor in itself is a very complex matter to quantify and qualify. In addition, the degree of odor that we experience is depending on the individual. The values we assign to the vast majority of odors are taught. However not every appreciation of odors is culturally determined: the primary purpose of odor is shedding or attracting. Our limbic system responds to questions like "Is this dangerous?" or "Is this edible?". Certain odors directly trigger a defensive response and that's a good thing. After all it can be an odor that is associated with something that is a direct danger. Other odors do just the opposite and evoke positive responses. The experience of the vast majority of all odors however depends on what one has learned and how something is labeled.

From biological, chemical and psychological point of view, odor and our perception of it is a very interesting field. Only fairly recently much research is done to the subject. Because of being a subjective topic, the hedonic value is the criterion most commonly used for odor measurements. This scale runs from-4 to + 4, in which -4 stands for unbearable and + 4 for very pleasant. A hedonic value of zero stands for neutral. This scale is used by governments and industries to determine the odor problem. It is also used to determine if the extent of the odor (the smell concentration) is still acceptable, where for an odor with a low hedonic value (more stench) a lower odor concentration is permissible.
In addition to the hedonic value of an odor, it is important to take the sensitivity to a odorous substance and its concentration into account. The sensitivity for an odor is expressed in a threshold value: 50% of that concentration at which a representative group of people perceive the odor. This concentration is usually expressed in the number of odor units per volume unit. The value of the odor concentration, expressed in odor units per m3 air (ouE/m3), is the number of times the odor in the air is to be diluted with odorless air to reach the threshold. 1 ouE/m3 is, by definition, the odor threshold as determined by a panel of 4-6 selected persons who statistically smell the same odor. The methodology for measuring odor concentrations is laid down in European standard EN 13725.


odor nuisance is the cumulative result of repeated disruptions by odor concentrations. The peak concentrations usually determine the extent to which people experience discomfort, whether or not affected by odor habituation. This discomfort is often reflected in changed behavior. This modified behavior can manifest itself active (e.g. complain, close windows, less sitting in the garden, no more inviting acquaintances) or passively (e.g. through different negative signals in survey responses). Bad odors are usually only annoying, but can also affect: one can feel less pleasant, the other gets headaches or feels nauseated. odor nuisance can hence lead to both physical and mental deterioration of the welfare (health effects and negative experience). The extent to which depends, among other things, on a person's sensitivity to smell, which for every human is unique.

Many factors contribute to the perception of odor nuisance: a low hedonic value, a high frequency of exposure, the local situation, a problem-oriented communication style, a negative attitude towards the source or the government or the fear of increase of the odor concentration and its effects for welfare and health. In fact the local nuisance can be actually greater than that could be calculated on the basis of the general relationship between odor concentration and odor nuisance. With this we often have very complex situations in which objectification and cooperation are often the only tools available.

As Aerox we always focus on this objectification and cooperation. The extra investment in time always delivers great benefits later in the process. The final result of the joint efforts is that the surrounding areas of our customers worldwide are ensured of fresh air and thus quality of life.

Erik C. Versteeg, Managing Director, Aerox B.V., 12 sept 2017

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