Editorial Feature

Olfactometer for the Measurement of Ambient Odor Concentrations

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Article updated on 09/03/20 by Priyom Bose 

ISO 5492:2008 defined odor as an organoleptic characteristic perceptible by the olfactory organ (including nerves) on smelling certain volatile substances. The word “olfaction” means the sense of smell.

Odorant is a substance which incites the human olfactory system so that an odor is perceived. The odor is given by the interaction of different volatile chemical species, including sulfur compounds (e.g. sulfides, mercaptans), nitrogen compounds (e.g. ammonia, amines), and volatile organic compounds (e.g. esters, acids, aldehydes, ketones, alcohols).

Analysis of odorous air chemical composition determines the type of approach used to characterize odorants. Unpleasant odors may trigger a variety of emotional and undesirable reactions in human beings, varying from annoyance to adverse health effects. It may lead to a reduced quality of life.

An olfactometer is a device that precisely detects and measures odors at various concentrations. It is normally a hand-held tool having small filter pads through which air can be transferred.

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Types of Olfactometers

The olfactometers are of two types as follows:

  • Flow Olfactometer – it is a complex instrument that generates well-defined stimuli in the nose without any thermal or tactile stimulation. It produces a constantly heated and humidified airflow that continuously runs through the nose of the human subject.
  • Dynamic Olfactometer – this version of olfactometers is a new generation instrument that quantifies odors with the help of a panel to allow evaluation of the relative intensity of odors, odor concentration, and odor threshold determination.

Working Principle

Dynamic olfactometry is the most commonly used technique which employs an odor panel consisting of a group of trained odor assessors for analyzing the odor samples. During this test procedure, an odor-free gas acting as a reference and a diluted odorous mixture are separately introduced into two sniffing ports so that the odor panel will sniff the sample starting with a very high dilution.

If the panelists are unable to determine the difference in three presentations, the panel leader will decrease gas diluting ratio by increasing the amount of sample air, and the process continues from the beginning. With the help of feedback from panelists over a range of dilution settings, the concentration of odor can be calculated from individual threshold estimates and expressed as odor unit per cubic meter.

Limitations of Dynamic Olfactometry

Although dynamic olfactometry represents the standardized objective method for the determination of odor concentration, it has some limitations.

Firstly, dynamic olfactometry provides point odor concentration data, which is not sufficient to evaluate all kinds of the olfactory nuisance. This is because dynamic olfactometry does not allow performing continuous and field measurements that are useful for monitoring the industrial processes causing odor emissions.

Dynamic olfactometry studies the entire odor mixture and does not discriminate the single chemical compounds and their contribution to the odor concentrations.

Types of Olfactometers

On the present market, there are different types of olfactometers, among which the following two are most common:

  • 'Yes/no' olfactometers: from the sniffing port odorless air or air with odor comes out alternatively and the panelist shall indicate on the evaluation card if he/she detects the odor or not.
  • 'Forced-choice' olfactometers: includes two or three different sniffing ports and each panelist shall indicate from which sniffing port the odor comes from.

The human olfactory system is considered as the most important and effective analytical device for odor evaluation, yet there is a demand for more objective analytical methods. With the discovery of materials with chemo-electronic properties, sensor-based machine olfaction potentially imitating the biological system has been developed.

Applications

  • Evaluation of removal efficiency of odor control technology
  • Evaluation of the relative intensity of odors
  • Measurement of odor detection threshold
  • Identification of causes of odor problems
  • Electrophysiological and psychophysical studies of animal and human response

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