Posted by Thierry Page on Tue, Dec 21, 2010 @ 11:48 AM
Those of you following our blog on Odor management have seen us try to be serious about odors and olfactometry with people used to sniff out odors in olfactory port.
Please allow us a little prank, a joke on olfactometry. This cartoon is the gift of a friend portraying the concept of olfactometry in a comic.
The Odotech team wishes you Happy Holidays and a wonderful 2011
Posted by Thierry Page on Sat, Dec 18, 2010 @ 11:28 AM
We are honoured to present you this second part of a special blog edition written by our guest author Dr. Johannes Frasnelli.
Dr. Frasnelli specialises in odor perception. He conducts research in the field of neurophysiology of smell and taste as well as therapy in loss of the chemical senses.
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When odor molecules reach the olfactory mucosa at the top of the nasal cavity, they get in contact with certain cells, the olfactory receptor neurons. The main part of these cells (the cell body) is located within the mucosa; but some branches, called cilia, reach the surface of the mucosa and are therefore exposed to the air in the nasal cavity. On these cilia we find the olfactory receptors. We humans have approximately 200 different olfactory receptors. Some animals, such as rats and dogs have many more olfactory receptors. The interesting thing is that, although we have so many different olfactory receptors, each and every olfactory receptor neuron carries only one receptor. Since the olfactory receptor neuron is therefore characterised by the receptor it carries, we can say that we have approximately 200 different olfactory receptor neurons in our olfactory mucosa. We could give our odor receptor names, for example “A-receptor”, “B-receptor”, “C-receptor”, etc. Then the olfactory receptor cells which carry the “A-receptor” would be a “A-specific” cell, or an “A-cell”. So, we have “A-cells”, “B-cells”, “C-cells”, etc. Within the olfactory mucosa, the different olfactory receptor cells are distributed completely at random.
As soon as an odor molecule reaches an olfactory receptor, the olfactory receptor cell is activated and sends a signal to the brain. But not every odor molecule activates all olfactory receptor neurons, because then all odors would smell the same. In order for the olfactory receptor neuron to be activated the odor molecules has to fit to the olfactory receptor as a key fits into a lock. However, this key-lock relationship is not very specific, but it is rather like middle age keys and middle age locks. In those old days one key could open several different locks; similarly an odor molecule fits into several different olfactory receptors and can therefore activate several different olfactory receptor neurons. So, for example, a ROSE odor molecule could activate the “R-cells”, the “O-cells”, the “S-cells”, and the “E-cells”.
In addition, one lock could be opened by several different keys. Similarly, several different odor molecules fit into the same olfactory receptor; therefore the olfactory receptor neuron which carries this particular receptor could be activated by several different odor molecules. For example, the “S-cell” could be activated by a ROSE-molecule, but also by a JASMINE-molecule, etc.
Now we can imagine what happens when we smell: Odor molecules reach the nasal cavity and there the olfactory mucosa. The odor molecules will reach olfactory receptors and activate the according olfactory receptor cells. Then the different olfactory receptor cells will send their signal to the brain. In order for the brain to recognize a certain odor, the complete information has to arrive. If the brain receives just the signal from the “S-cells”, it may be able to tell that this was a flowery odor, but it will not be able to tell whether the odor was ROSE or JASMINE. In order for the brain to be able to distinguish between many odors, the brain needs the information from all olfactory receptor cells.
Remember that the cell body is in the mucosa, the lower parts (the cilia) with the receptors are actually on the surface of the mucosa. On the upper side, the olfactory receptor cells carry an extension, the so called axon. This axon travels from the nasal mucosa through the bone of the skull to the brain. SWhen we say that the olfactory receptor cells send the information to the brain, they do it via these structures. The axons of all olfactory receptor neurons together form the olfactory nerve, the first cranial nerve. The axons reach a brain structure called the olfactory bulb. The olfactory bulb is just above the nose, but already part of the brain. Within the olfactory bulb, axons end in some ball-like structure, the so called glomeruli. These are however very small balls, they measure approximately a tenth of a millimetre.
Here something interesting happens. The axons of all the olfactory receptor cells carrying one specific receptor (for example, the “A-receptor”) all terminate at the same glomerulus. Furthermore, at this glomerulus no axon from other olfactory receptor cells end. We can therefore call it the “A-glomerulus”. Whenever an odor molecule reaches the olfactory mucosa and activates some olfactory receptor cells, the according glomerulus gets activated. Since we said we have 200 different olfactory receptors, and 200 different olfactory receptor neurons, we should also have 200 glomeruli in our olfactory bulb.
Source: Patrick J. Lynch, medical illustrator
Figure legend:
- Olfactory bulb
- Mitral cells
- Bone
- Nasal Epithelium
- Glomerulus
- Olfactory receptor cells
In the figure, the receptor cells carrying different names are drawn in different colors.
Now we know everything to understand how the olfactory system works: When we smell a ROSE-odor, the ROSE-molecules reach the nasal cavity. They will fit into different receptors (the “R-receptor”, the “O-receptor”, the “S-receptor”, and the “E-receptor”) and therefore activate 4 different sets of olfactory receptor neurons (the “R-cells”, the “O-cells”, the “S-cells”, and the “E-cells”). Then the information will travel to the olfactory bulb, and four different glomeruli will light up: the “R-glomerulus”, the “O-glomerulus”, the “S-glomerulus” and the “E-glomerulus”. Then the brain has nothing more to look on the olfactory bulb and recognize the pattern of activated glomeruli. In our case, the brain would see that R, O, S, and E light up in the olfactory bulb and then conclude that we smell a rose.
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About the author: Dr. Johannes Frasnelli Ph.D.
Dr. J. Frasnelli is a graduate of the Medical Schools of the University of Vienna (Austria; 2001; Dr. med. univ.) and the Technical University of Dresden (Germany; 2009; Priv.-Doz.). Since 2006 he work in Montreal, first as an Academic Trainee at the Montreal Neurological Institute, since 2008 as a Postdoctoral Fellow at the Department of Psychology at the Université de Montréal. He currently hold a fellowship of the FRSQ. Dr. Frasnelli research interest is the neurophysiology of smell and taste as well as therapy in loss of the chemical senses.
Contact information: johannes.frasnelii@umontreal.ca
Personal links:
Interesting links:
Posted by Thierry Page on Wed, Dec 15, 2010 @ 05:50 PM
We are honoured to present you this special blog edition written by our guest author Dr. Johannes Frasnelli.
Dr. Frasnelli specialises in odor perception. He conducts research in the field of neurophysiology of smell and taste as well as therapy in loss of the chemical senses.
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We can smell many, probably thousands of different odors. Whenever we smell something, odor molecules are reaching the olfactory receptors in our nose. Usually it is a mix of many different odor molecules which in combination gives us a certain smell. Coffee odor for example is a mix of dozens of different odor molecules. Odor molecules are chemical substances. Even if we are smelling an odor from a natural source, chemical substances are releaesed from the odor source and which reach our nose. An odor source is everything which has a smell. For example, one of the main components of the smell of cloves is eugenol, a chemical substance. We can buy eugenol in the pharmacy and smell it. It smells exactly like the cloves we can buy in the grocery store (although it may smell a bit stronger).
In order that we can smell odors, odor molecules have to reach the inside of our nose, the nasal cavity. This usually happens when we breathe in. During every breath, the air surrounding us is soaked into our lungs. Within this air we find many different odor molecules. If we are standing in a bakery, many different odor molecules from bread will be all over the room. Every time we breathe in, these bread odor molecules will also be inhaled with the room air. And every time we breathe in, we will smell the nice odor of fresh bread.
Odor molecules do not have to go all the way to the lungs in order to be smelled. Instead they just have to reach the so called olfactory mucosa, which is located in the nasal cavity. Another term for olfactory mucosa is olfactory epithelium. As every opening of our body, the nasal cavity is lined with mucosa. However only in the top portion of the nasal cavity, the nasal mucosa carries certain cells, the olfactory receptor cells. And the odor molecules have to reach these olfactory receptor cells in order for us to smell them.
When we look at our own face in the mirror, we see our nose in the middle of the face. Everyone thinks he knows his nose very well. However, one may be surprised to hear that the portion of the nose which is visible from the outside is only a minor part of it. In fact, our nose is constructed similar to a gothic cathedral, and we can only see the façade. It is only once we enter the gothic cathedral by the gate (the nostril), we see the inside. Our nose-cathedral is very narrow, but goes very far back, and very high up. In the very back, something like 5 to 8 centimeters inside the nasal cavity, we reach the nasopharynx, which is the uppermost part of our throat. From here we can descent towards the lungs. On the way there we could reach our mouth (from backwards), the esophagus, which leads to the stomach and the wind pipe or trachea, which leads to the lungs. But we are interested in looking upwards. When we look up to the ceiling of the nasal cavity, approximately 5 cm away from the nostril, we are looking directly onto the olfactory mucosa. When looking from outside, the olfactory epithelium is located right between our eyes. So, odor molecules have to reach the top of the nasal cavity in order to be smelled.
Source: Patrick J. Lynch, medical illustrator
When we inhale normally, most of the odor molecules stay on the floor of the nasal cavity, and only few reach the top of the nasal cavity. When we sniff, however, we are causing turbulences in the nasal cavity and much more odor molecules will reach the olfactory mucosa at the top of the nasal cavity – and we will perceive a stronger smell.
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About the author: Dr. Johannes Frasnelli Ph.D.
Dr. J. Frasnelli is a graduate of the Medical Schools of the University of Vienna (Austria; 2001; Dr. med. univ.) and the Technical University of Dresden (Germany; 2009; Priv.-Doz.). Since 2006 he work in Montreal, first as an Academic Trainee at the Montreal Neurological Institute, since 2008 as a Postdoctoral Fellow at the Department of Psychology at the Université de Montréal. He currently hold a fellowship of the FRSQ. Dr. Frasnelli research interest is the neurophysiology of smell and taste as well as therapy in loss of the chemical senses.
Contact information: johannes.frasnelii@umontreal.ca
Personal links:
Interesting links:
Posted by Thierry Page on Mon, Dec 13, 2010 @ 08:21 AM
However, it has been scientifically demonstrated over the last decade that H2S is only partially responsible for the odors perceived offsite. Monitoring H2S for odor problems may lead to underestimations of the odor intensity or completely missing the contribution of other odorous compounds (VOCs, ammonia & amines, other sulfurous compounds, etc). We invite you to read these blogs:
Olfactometric quantification is essential for quantifying the overall odor level (odor concentration). Many operators today recognize the value of odor monitoring expressed in odor units for understanding odor complaints and improving their production processes. (http://blog.odotech.com/bid/51233/Pima-County-Marks-1-Year-of-Odor-Management-Innovation). However, there is a continuity problem in switching from H2S to Odor monitoring. How to relate the H2S historical data to the new Odor measurements ?
It is now possible to bridge the gap between H2S and Odor real-time monitoring by merging OdoWatch (odor monitoring with eNoses) with the new OdoSulf technology (H2S monitoring). Simultaneous H2S and Odor on the same platform is made easy with two 100% compatible technologies.
OdoSulf is the first automated system designed specifically for Hydrogen Sulfide (H2S) emissions with atmospheric dispersion plume display. The sulfNoses (H2S detectors) can measure H2S down to 2 ppb at the perimeter and up to 100 ppm at the emission source. The system delivers a real-time H2S atmospheric plume display. The data are then archived for future reference.
It is now possible with one air quality monitoring system to track real-time Odor and H2S. The eNoses and H2S monitors can be located at the sources and/or at the fenceline for the SulfNose. But all the sensors are integrated in one software to get H2S plumes and Odor plumes simultaneously and fenceline H2S logs. You can get alerted when odors are leaving your site, and know how far and were they travel.
Some of the possible uses of this combined H2S-Odor approach:
- Insure regulatory compliance
(Track the H2S values at the property boundaries)
- Reduce the cost and impact of air quality & Odor investigations
- Improve community relations
- Monitor the effectiveness of abatement actions taken
- Optimize process
- Manage proactively
- Manage off-site impacts and complaints
- The sulfNoses + eNoses at the emission sources plus real-time modeling quickly determine whether or not the H2S from the facility is causing an off-site impact at complaint location
- In case of an alert, they show immediately which of the site sources needs action.
- Access historical data as needed.
- Monitor trends or address complaints.
- Quantify H2S/Odor to optimize H2S/Odor emission controls.
- Implementation of controls can be prioritized.
Posted by Thierry Page on Sun, Dec 12, 2010 @ 08:21 AM
The sense of olfaction is complex. Odor perception is influenced by many factors unique to each individual as well as external environmental factors. The basis of odor perception is the contact between chemical molecules, mainly in the gaseous state, which can be detected by the olfactory epithelium.
From : Pour la science # 218
The odorous molecules come into contact with the olfactory epithelium at the top of the nasal cavity and stimulate multiple chemically cell receptors (see figures).
From : Pour la science # 218
The electrical impulses generated by the olfactory epithelium cells are transmitted via the olfactory nerve (first cranial nerve which passes through the skull through the cribriform plate) in the central olfactory system located in the limbic system. A branch of the fifth cranial nerve, the trigeminal, is the vehicle for the perception of irritation at the nose, the nasopharynx and the oropharynx, as well as the sensation of taste and smell.
From: LAFFORT P., Aspects of the olfactory information, chap 6 dans Characterization and control of odours and VOC in the process industries, VIGNERON S., HERMIA J., and CHAOUKI J. Eds, Studies in Environmental Science, 61, Amsterdam, The Netherlands, 1994.
The trigeminal nerve also contributes to assess the odor perception magnitude even without irritation. It is interesting to note that some molecules are detected as well by irritation as by olfaction: ammonia, NOx, Ozone, ect.
The perception of an odor by humans results from a stimulus. It includes key information as the odor intensity and odor quality. Our ability to collect this information makes the olfaction a very complex sense. All the biochemical parameters are not yet fully understood by specialists.
For the intensity, our sense of smell behaves much like our perception of hot or cold substances. The signal strength is very strong at the beginning then there is adaptation and gradual decline in signal strength (toe in a bath). In terms of odor quality, our sense of smell works similarly to taste: we can recognize, classify and assess the quality of an odor.
One of the quality of olfactometry is that a lot of the odor
perception complexity is tied in a reproducible quantified parameter: the odor concentration.
Related readings:
Posted by Thierry Page on Sat, Dec 11, 2010 @ 12:40 PM
We have seen the benefits of olfactometry in the blog Measurement of odor emissions – Olfactometry or chemical analysis?
In general, it is difficult to use the chemical analysis method for mixtures of odorous compounds due to the phenomena of 
synergy, inhibition and masking between different compounds (Gostelow et al., 2003).Complex mixtures, such as environmental air samples, contain many odorous compounds, generally at very low concentrations (Gostelow et al., 2001) (Schiffman et al., 2001) (Parker et al., 2002) (Filipy et al., 2006). To analyze all the odorous compounds that are present, the composition of the sample must be known in advance, and the detection limits of the chemical analysis devices are often too high to identify and quantify all these odorous compounds (Gostelow et al., 2003). Finally, the olfactory perception threshold values are not always available in the existing literature, the values reported vary by several orders of magnitude (AIHA, 1989) (US EPA, 1992), and the available references are not recent.
The effects of synergy and masking between different odorous compounds can be observed in samples. For example, in a sample of food odor, the volatile compounds were identified and regrouped in five key odorous families. This was done to study the effect on odor resulting from different combinations of the five groups of compounds (Hallier et al., 2004). Synergy and masking effects were thus observed.
Numerous researchers have studied odorous mixtures and have created models to predict the effect that the mixtures’ composition has on the perceived odor (composition and concentration) (Gostelow et al., 2003). In general, the use of these models is limited and applies only to the experimental conditions of the study. As well, the mixtures of compounds are mostly studied in the laboratory because of the complexity of mixed odors.
Studies have identified dominant odorous compounds in environmental samples. For example, a positive relation can be established between the odor concentration determined by olfactometry and the odor principle identified in the odor samples of liquid hog manure (Hobbs et al, 2000) and odor samples of composting mushrooms (Noble et al., 2001). 
However, these studies also show that a relation between the mixture composition and the odor concentration is still misunderstood and difficult to predict. For wastewater treatment processes, where H2S is the predominant odor, Gostelow and Parsons (2000, from Stuetz and Frechen 2001) show the values of r2 between the H2S and the odor concentrations to be as low as 7 to 69%.
Odor Perception Threshold Values
The American Industrial Hygiene Association (AIHA, 1989) compiled numerous studies and established a critical analysis of odor threshold values. The AIHA document is a recognized reference today and is often used as a source for odor threshold values. The scale of acceptable odor threshold values was 
established for H2S from 0,001 ppmv to 0,130 ppmv (1 µg/m3 to 181 µg/m3). The recommended value held by the AIHA (1989) is 0,0094 ppmv (13 µg/m3). H2S is a well-studied odorous compound and yet the AIHA proposes a scale of values for the threshold of two orders of magnitude, after their critical review. The example of H2S illustrates why it is often inappropriate to work with odor threshold values because reliable values are not always readily available. New studies with dynamic dilution olfactometers shows 0.0004 pmmv as perception threshold values.
Olfactometry analysis
Olfactometry generates standard sensory analyses, and the principal tool to measure odor characteristics is a trained jury of “noses” or a group of selected experts chosen according to rigorous and precise criteria. An olfactometer is a device designed to dilute the odorous gas samples and to present these dilutions to the jury. After obtaining the responses of the jury, a statistical treatment of the data permits the olfactometric result to be calculated.
Olfactometric analyses are tested in the laboratory (EN 13725 and ASTM E679-04) or in the field during which the odor samples are gathered and then exposed to the target population in the study area. However, olfactometric analyses of ambient air in the field are not recommended because of frequent variations of odor concentrations in ambient air and the low resolution of these methods.
Applications
In England, the Environmental Agency published a guide on the measure of H2S and the reduced sulphur totals at the source of ambient air (Environment Agency, 2001). This guide recommends that the measuring strategy be directly related to the objective of the measurement study. Thus, if the objective establishes the required abatement to eliminate the nuisance odor, it is specified in the guide that the odor concentration measurements expressed in odor units per cubic meter (o.u./m3) are more appropriate than the kind obtained through chemical measurement.
Conclusion
The main advantage of olfactometry is the direct correlation between the odor and the sensitivity of the detector used, i.e. the human nose.
Despite the advantages of the classic analytical methods (accuracy, reproducibility, etc.), olfactometry remains the best available approach to measure odors directly, in order to objectively quantify the perception of odors.
References
- AIHA (1989). Odor Thresholds for Chemicals with Established Occupational Health Standards. American Industrial Hygiene Association.
- ASTM (1997). E679-91 (reapproved 1997) - Standard Practice for Determination of Odor and Taste Thresholds By a Forced-Choice Ascending Concentration Series Method of Limits. American Society for Testing and Materials: p. 34-38.
- CEN (2003). EN 13725 - Air quality - Determination of odour concentration by dynamic olfactometry. European Committee for Standardization: p. 71.
- Environment Agency (2001). Technical Guidance Note M13: Monitoring hydrogen sulphide and total reduced sulphur in atmospheric releases and ambient air. ISBN 1 857 05696 5. Environment Agency’s National
- Compliance Assessment Service, England and Wales. www.environment-agency.gov.uk/business/techguide/monitoring/m13.html
- Filipy, J., B. Rumburg, et al. (2006). "Identification and quantification of volatile organic compounds from a dairy." Atmospheric Environment 40: 1480-1494.
- Gostelow, P., SA Parsons (2000). “Sewage treatment works odour measurements.” Wat. Sci.Technol. 41(6), 33-40.
- Gostelow, P., SA Parsons, RM Stuetz (2001). “Odour Measurements for Sewage Treatment Works.” Water Research 35(3): 579-597.
- Stuetz R. and Frechen FB (2001). “ Odours in Wastewater Treatment. Measurement, Modelling and Control “. Gostelow, P., P.J. Longhurst, SA Parsons, RM Stuetz (2003). Sampling for Measurement of Odours. London
- UK, IWA, 80 pages. Hallier, A., P. Courcoux, et al. (2004). "New gas chromatography–olfactometric investigative method, and its application to cooked Silurus glanis (European catfish) odor characterization." Journal of Chromatography A 1056: 201-208.
- Hobbs, P. J., T. H. Misselbrook, T. Dhanoa and K. Persaud (2000). "Development of a relationship between olfactory response and major odorants from organic wastes." Journal of the science of food and agriculture Vol. 81: pp. 188-193.
- Noble, R., P. J. Hobbs, A. Dobrovin-Pennington, T. H. Misselbrook and A. Mead (2001). "Olfactory Response to Mushroom Composting Emissions as a Function of Chemical Concentration." Journal of environmental quality Vol. 30: pp. 760–767.
- Parker, T., J. Dottridge and S. Kelly (2002). R&D Technical Report P1-438/TR: Investigation of the Composition and Emissions of Trace Components in Landfill Gas, Environment Agency, England and Wales.
- Schiffman, S. S., J. L. Bennett, et al. (2001). "Quantification of odors and odorants from swine operations in North Carolina." Agricultural and Forest Meteorology 108: 213-240.
- US EPA (1992). “Reference Guide to Odor Thresholds for Hazardous Air Pollutants Listed in the Clean Air Act Amendments of 1990” (#EPA600/R-92/047). TRC Environmental Consultants Inc., S. S. Cha, J. R. Mellberg, G. L. Ginsberg, K. E. Brown, K. Raab and J. C. Coco. US EPA, pp. 93.