Making Sense of Smells – Communicating Odors to Diverse Audiences - Part 1
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Proceedings available at: http://www.extension.org/67597 Smell is perhaps the least understood of our five senses. Yet, the human perception of odor may mean the difference between war and peace for a livestock farmer and his neighbors. Because the science of smells is complex, there is a tendency to run straight for the organic chemistry book when we try to describe farmstead odors. This approach goes right over the heads of most people. There must be a better way to communicate odors to diverse audiences. Come to this workshop and find out how.
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Making Sense of Smells – Communicating Odors to Diverse Audiences - Part 1
- 1. Making Sense of Smells Discussing Odors with Diverse Audiences Douglas W. Hamilton Waste Management Specialist Biosystems and Agricultural Engineering
- 5. Odors need not be so mysterious … 1. They have structure 2. They are measurable
- 6. Odors need not be so mysterious … 1. They have structure
- 7. Rose de Grasse is characterized by a honey note, resembling very slightly a delicate peppery note, shading off into a light tonality of natural carnation … it is possible to perceive a slightly green odor … Billot, M. and F.V. Wells. Perfumery Technology: Art, Science, Industry. New York:John Wiley. Perfume Structure Perfume Fragrances are mixtures of Notes
- 8. Rose de Grasse is characterized by a honey note, resembling very slightly a delicate peppery note, shading off into a light tonality of natural carnation … it is possible to perceive a slightly green odor … Billot, M. and F.V. Wells. Perfumery Technology: Art, Science, Industry. New York:John Wiley. Perfume Structure Perfume Fragrances are mixtures of Notes Notes are mixtures of Odorants
- 9. Hyacinth Green Base No. 10 Hydroxycitonellel Phenylethyl acetate Phenylethyl alcohol isoEugenol Cinnamic alcohol Phenylacetaldehyde Phenylacetaldehyde dimethyl acetal Folial Benzyl acetate Phenylethyl formate Terpineol Rhodiniol alpha-Amaylcinnamic aldehyde Paracetone Dimethyl phthalate Perfume Structure Perfume Fragrances are mixtures of Notes Notes are mixtures of Odorants Odorants are individual Chemicals
- 10. Perfume Fragrances are mixtures of Notes Farmstead Odors are mixtures of Notes Notes are mixtures of Odorants Notes are groups of Odorants Odorants are individual Chemicals Odorants are individual Chemicals Odor Structure
- 11. Farmstead Odorant Groups Organic Acids Acetic Acid Propionic Acid Butanoic Acid Iso-Valeric Acid Pentanoic Acid Alcohols, Aldehydes, Ketones Methanol Formaldehyde Acetone Methyl Ethyl Ketone Nitrogen Compounds Ammonia Methyl amine Dimethyl amine Diethyl amine Indole Skatole Phenolic Compounds Phenol p-Cresol Sulfuric Compounds Hydrogen Sulfide Methyl mercaptan Dimethyl sulfide Diethyl sulfide
- 12. Odors need not be so mysterious … 1. They have structure 2. They are measurable
- 13. Odor Measurement How does it smell? How Long? How Much? How Strong?
- 14. Odor Measurement How does it smell? How Long? How Much? How Strong? Character
- 15. Odor Measurement How does it smell? How Long? How Much? How Strong? Character Persistence
- 16. Odor Measurement How does it smell? How Long? How Much? How Strong? Character Persistence Concentration
- 17. Odor Measurement How does it smell? How Long? How Much? How Strong? Character Persistence Concentration Intensity
- 19. Notes Odors Character Verbal Description Persistence Concentration Intensity Measuring Notes and Odors
- 20. Character Organic Acids Acetic Acid Propionic Acid Butanoic Acid Iso-Valeric Acid Pentanoic Acid Alcohols, Aldehydes, Ketones Methanol Formaldehyde Acetone Methyl Ethyl Ketone Nitrogen Compounds Ammonia Methyl amine Dimethyl amine Diethyl amine Indole Skatole Phenolic Compounds Phenol p-Cresol Sulfuric Compounds Hydrogen Sulfide Methyl mercaptan Dimethyl sulfide Diethyl sulfide
- 21. Character Organic Acids Acetic Acid Propionic Acid Butanoic Acid Iso-Valeric Acid Pentanoic Acid Alcohols, Aldehydes, Ketones Methanol Formaldehyde Acetone Methyl Ethyl Ketone Nitrogen Compounds Ammonia Methyl amine Dimethyl amine Diethyl amine Indole Skatole Phenolic Compounds Phenol p-Cresol Sulfuric Compounds Hydrogen Sulfide Methyl mercaptan Dimethyl sulfide Diethyl sulfide
- 22. Character Organic Acids Acetic Acid Propionic Acid Butanoic Acid Iso-Valeric Acid Pentanoic Acid Alcohols, Aldehydes, Ketones Methanol Formaldehyde Acetone Methyl Ethyl Ketone Nitrogen Compounds Ammonia Methyl amine Dimethyl amine Diethyl amine Indole Skatole Phenolic Compounds Phenol p-Cresol Sulfuric Compounds Hydrogen Sulfide Methyl mercaptan Dimethyl sulfide Diethyl sulfide
- 23. Character Organic Acids Acetic Acid Propionic Acid Butanoic Acid Iso-Valeric Acid Pentanoic Acid Alcohols, Aldehydes, Ketones Methanol Formaldehyde Acetone Methyl Ethyl Ketone Nitrogen Compounds Ammonia Methyl amine Dimethyl amine Diethyl amine Indole Skatole Phenolic Compounds Phenol p-Cresol Sulfuric Compounds Hydrogen Sulfide Methyl mercaptan Dimethyl sulfide Diethyl sulfide
- 24. Character Organic Acids Acetic Acid Propionic Acid Butanoic Acid Iso-Valeric Acid Pentanoic Acid Alcohols, Aldehydes, Ketones Methanol Formaldehyde Acetone Methyl Ethyl Ketone Nitrogen Compounds Ammonia Methyl amine Dimethyl amine Diethyl amine Indole Skatole Phenolic Compounds Phenol p-Cresol Sulfuric Compounds Hydrogen Sulfide Methyl mercaptan Dimethyl sulfide Diethyl sulfide
- 25. Character Organic Acids Acetic Acid Propionic Acid Butanoic Acid Iso-Valeric Acid Pentanoic Acid Alcohols, Aldehydes, Ketones Methanol Formaldehyde Acetone Methyl Ethyl Ketone Nitrogen Compounds Ammonia Methyl amine Dimethyl amine Diethyl amine Indole Skatole Phenolic Compounds Phenol p-Cresol Sulfuric Compounds Hydrogen Sulfide Methyl mercaptan Dimethyl sulfide Diethyl sulfide
- 26. Notes Odors Character Verbal Description Persistence Odor Chord Concentration Intensity Measuring Notes and Odors
- 27. Notes Odors Character Verbal Description Persistence Top Note Middle Note Base Note Odor Chord Concentration Intensity Measuring Notes and Odors
- 28. Persistence Top Notes Middle Notes Base Notes Hydrogen Sulfide Ammonia Aldehydes Alcohols Ketones Amines Mercaptans Short Organic Sulfides Organic Acids Phenolic Compounds Indole Skatole Long Organic Sulfides
- 29. Persistence Top Notes Middle Notes Base Notes Hydrogen Sulfide Ammonia Aldehydes Alcohols Ketones Amines Mercaptans Short Organic Sulfides Organic Acids Phenolic Compounds Indole Skatole Long Organic Sulfides
- 30. Persistence Top Notes Middle Notes Base Notes Hydrogen Sulfide Ammonia Aldehydes Alcohols Ketones Amines Mercaptans Short Organic Sulfides Organic Acids Phenolic Compounds Indole Skatole Long Organic Sulfides
- 31. Persistence Top Notes Middle Notes Base Notes Hydrogen Sulfide Ammonia Aldehydes Alcohols Ketones Amines Mercaptans Short Organic Sulfides Organic Acids Phenolic Compounds Indole Skatole Long Organic Sulfides
- 32. Persistence Top Notes Middle Notes Base Notes Hydrogen Sulfide Ammonia Aldehydes Alcohols Ketones Amines Mercaptans Short Organic Sulfides Organic Acids Phenolic Compounds Indole Skatole Long Organic Sulfides
- 33. Persistence Top Notes Middle Notes Base Notes Hydrogen Sulfide Ammonia Aldehydes Alcohols Ketones Amines Mercaptans Short Organic Sulfides Organic Acids Phenolic Compounds Indole Skatole Long Organic Sulfides
- 34. Persistence Top Notes Middle Notes Base Notes Hydrogen Sulfide Ammonia Aldehydes Alcohols Ketones Amines Mercaptans Short Organic Sulfides Organic Acids Phenolic Compounds Indole Skatole Long Organic Sulfides
- 35. Persistence Top Notes Middle Notes Base Notes Hydrogen Sulfide Ammonia Aldehydes Alcohols Ketones Amines Mercaptans Short Organic Sulfides Organic Acids Phenolic Compounds Indole Skatole Long Organic Sulfides
- 36. Persistence Top Notes Middle Notes Base Notes Hydrogen Sulfide Ammonia Aldehydes Alcohols Ketones Amines Mercaptans Short Organic Sulfides Organic Acids Phenolic Compounds Indole Skatole Long Organic Sulfides
- 37. Persistence Top Notes Middle Notes Base Notes Hydrogen Sulfide Ammonia Aldehydes Alcohols Ketones Amines Mercaptans Short Organic Sulfides Organic Acids Phenolic Compounds Indole Skatole Long Organic Sulfides
- 38. Persistence Top Notes Middle Notes Base Notes Hydrogen Sulfide Ammonia Aldehydes Alcohols Ketones Amines Mercaptans Short Organic Sulfides Organic Acids Phenolic Compounds Indole Skatole Long Organic Sulfides
- 39. Persistence Top Notes Middle Notes Base Notes Hydrogen Sulfide Ammonia Aldehydes Alcohols Ketones Amines Mercaptans Short Organic Sulfides Organic Acids Phenolic Compounds Indole Skatole Long Organic Sulfides
- 40. Notes Odors Character Verbal Description Persistence Top Note Middle Note Base Note Odor Chord Concentration Detection Level Recognition Level Intensity Measuring Notes and Odors
- 42. NH3 Recognition Level = 37,000 ppb
- 44. NH3 Detection Level = 17 ppb
- 45. NH3 Acute Hazard = 50,000 to 100,000 ppb
- 46. NH3 Chronic Exposure = 25,000 ppb
- 47. Notes Odors Character Verbal Description Persistence Top Note Middle Note Base Note Odor Chord Concentration Detection Level Recognition Level OU Intensity Measuring Farmstead Odors
- 49. Olfactometry Choosing presidents and measuring odors are very similar processes. OPINIONS ARE IMPORTANT AND THE MAJORITY RULES.
- 55. 1/10
- 57. 1/100
- 59. 1/200
- 61. 1/500
- 63. 1/1,000
- 65. 1/2,000
- 67. 1/4,000
- 69. 1/8,000
- 71. 1/16,000
- 72. 1/32,000
- 73. 1/16,000
- 74. 1 OU = dilution to threshold
- 75. 1 OU = 1/16,000
- 76. OU = 16,000
- 79. Notes Odors Character Verbal Description Persistence Top Note Middle Note Base Note Odor Chord Concentration Detection Level Recognition Level OU Intensity Intensity Measuring Notes and Odors
- 80. Two Methods for Intensity 1. Referencing Suprathreshold 2. Descriptive Category Scale
- 81. Odors are compared to standards of known intensity using dilutions of 1-Butanol CH3CH2CH2OH Referencing Suprathreshold Odor Intensity
- 82. Port 1 2 3 4 5 6 7 8 www.rka-inc.com Purdue Agricultural Air Quality Laboratory Referencing Suprathreshold Odor Intensity
- 83. Port vol/vol 1-butanol ppm 1 12 2 24 3 48 4 96 5 194 6 388 7 775 8 1,550 www.rka-inc.com Referencing Suprathreshold Odor Intensity
- 84. Descriptive Scale Odor Intensity Panel rates Intensity on a scale independent of an external standard
- 86. 0 1 2 3 4 5 6 1 10 100 1000 Odor Concentration (OU) OdorIntensity Measured Swine Odor Relationship 6 = Extremely strong 5 = Very Strong 4 = Strong 3 = Distinct 2 = Faint 1 = Very Faint 0 = No Odor Misselbrook, et al. 1993
- 87. Measured Odor Relationships 6 = Extremely strong 5 = Very Strong 4 = Strong 3 = Distinct 2 = Faint 1 = Very Faint 0 = No Odor Misselbrook et al, 1993
- 88. Notes Odors Character Verbal Description Offensiveness Persistence Top Note Middle Note Base Note Odor Chord Concentration Detection Level Recognition Level OU Intensity Intensity Measuring Notes and Odors
- 89. Offensiveness by Olfactometry 1. Equal Intensity samples are presented to panel.
- 90. Offensiveness by Olfactometry 1. Equal Intensity samples are presented to panel 2. Panel rates offensiveness on a descriptive scale.
- 92. Offensiveness is an Intrinsic Property of an Odor A odor will be equally offensive, no matter how strong.
- 94. Experimental Hypothesis A odor will be equally offensive, no matter how strong.
- 96. Sample 1 How Strong? _____ How Pleasant? ______
- 97. Sniff Test A B C D How Strong? How Pleasant? Intensity Scale = 0 to 6
- 98. Intensity Scale 0 = no odor 1 = very faint 2 = faint 3 = distinct 4 = strong 5 = very strong 6 = extremely strong
- 100. Sniff Test A B C D How Strong? How Pleasant Intensity Scale = 0 to 6 Pleasantness Scale = -3 to 3
- 101. Carmichael/Spitler Pleasantness Scale -3 = Very Unpleasant -2 = Unpleasant -1 = Slightly Unpleasant 0 = Neutral 1 = Slightly Pleasing 2 = Pleasing 3 = Very Pleasing
Editor's Notes
- We don’t need to despair about the mysteries of odors, because they have a “structure”, and they can be measured.
- You might ask, “How can something we can’t see or feel have structure?” Structure is just another way of saying that odors can be broken down into smaller parts. Because we can break them down into parts, we can also describe and recreate the structures. Think about it. Humans have been buying and selling smell for about 3,000 years. Billions of dollars pass through the perfume industry each year. People who make perfume have a way to describe and recreate their fragrances, and they have been doing so long before the advent of modern chemistry.
- Each perfume fragrance is made up of a mixture of notes. Notes are individual smells recognized by a trained sniffer. Rose de Grasse is a common perfume fragrance. It has been described as, “characterized by a honey note, resembling verry slightly a delicate peppery note.” The sniffer quoted here said he could recognize a honey smell, hence Rosse de Grasse has a honey note -- but not just any honey note – a honey note with a hint of pepper. He goes on, “shading off into a light tonality of natural carnation.” Once the honey note passed, the sniffer smelled carnation -- a distinctive flowery note. Then he says, “it is possible to perceive a slightly green odor” A slight green – or plant-like – note.
- What makes a “note” smell peppery, or plant-like? Each note is a mixture of many odorants – individual odor causing chemicals. The green note in Rose de Grasse could be made up of thousands of odorants. Here’s where the gas chromatographs and chemistry books usually come in.
- This is a list of odorants found in a green note called Hyacinth Green Base Number 10. You’ll see that it has a lot of odorant chemicals that end in -ol, -el, -hyde, and -one. These come from a group of chemicals called the alchohols, aledhydes and ketones. A group of chemicals responsible for many of the plant-like smells found in nature.
- We can look at farmstead odors the same way as perfume. Odors are not usually one pure smell. They made of many, many odorants. Certain groups of odorants form particular smells in the mixture, and these we can call notes.
- The notes in manure odors come from five groups of chemicals. Don’t worry about remembering the odorant names, or even the names of the groups. We will show a simplified way of describing these notes in the next part of this series.
- We don’t have to think that odors are mysterious, because they can be measured.
- We can describe any odor by asking four basic questions. What does the odor smell like? How long does the odor last after it is introduced? How many odorants are in the air? And, how strong is the odor?
- What an odor smells like is described by a measurement called character.
- How long an odor lasts is the measurement of it persistence.
- We answer the question of how many odorants are detectible by measuring the concentration of odorants in the air.
- We do no actually perceive the concentration of odor, but respond to the strength of an odor. Measurement of odor strength is called Intensity.
- As we learned in the previous section, odors are made of complex mixtures of notes. Notes and odors are measured in slightlydifferent ways. In this segment, we will concentrate on the measurement of notes. In the following segments, we will show how olfactometry is used measure the concentration, character, and intensity of odors.
- Character is conveyed through a verbal description of the note. We describe notes as fruity, flowery, peppery, earthy, etc.
- In the previous segment, we said that the notes that make up manure odors come from five general groups of chemicals. One of the major problems of describing odors is we often jump right to calling out the chemical compounds in odors. This overuse of chemical names only confuses folks. Let’s look at a simple way to communicate the notes played by these five groups.
- Perfumists use “green” to describe plant-like smells in their concoctions. Green notes in perfume are made by some of the same odorants found in farmstead odors. The alcohols, aldehydes, and ketones group creates the “green “ or plant-like notes smelled on the farm. Alcohols and Ketones often have “sweet” smells. Some people say that freshly excreted horse and cow manure have a sweet smell. These are the green notes of alcohols and ketones. Many “grassy” smells come from aldehydes; however, the simplest aldehyde , formaldehyde, is irritating at fairly low concentrations.
- Let’s call the organic acids the “black nasties”. Organic acids are what give dirty stocks their funk. They are what makes pigs smell like pigs; and goats goaty. Acetic Acid is vinegar. Butanoic or Butyric acids gives rancid butter its distinct smell. Some longer chained acids are what give rotting meat its “unpleasant air”.
- Many amines, which are simple nitrogen containing compounds, have “fishy” smells, so we give nitrogen containing compounds the blue note. Ammonia has its own distinctive, irritating smell. An old fashion word for excrement is “Scat”. Skatole is the compound that gives human feces its unforgettable odor. Indole is a close cousin to Skatole, but believe it or not, Indole is a major component in perfumes. In small doses, Indole gives a flowery smell, and is a major component in Gardenia notes. At higher concentrations, Indole smells more like Skatole.
- The phenolic compounds are responsible for “earthy” smells, so we’ll give them the color brown.
- Sulfur containing compounds are the “screaming reds”. They produce some of the most penetrating odors smelled on the farm. Hydrogen sulfide has the smell of rotten eggs. Methyl mercaptan is the main component of “skunk” odor. Mercaptans are also added to give a smell to otherwise odorless natural gas. Organic sulfide compounds give us cabbage and rotting garbage smells.
- Odors, like perfumes, are mixtures of many notes. You may have guessed that perfumers use musical terms, such as “note”, to describe their fragrances. A mixture of notes blend to form an odor “chord”. An expensive perfume won’t be a one note tune, but a chord of many notes, and some notes last longer than others. Perfume may smell sharp and fruity at the beginning of the evening, and more subtle and smoky at the end.
- Perfumes are comprised of three basic sets of notes. The short lasting top notes. The loner lasting middle notes -- sometimes called filler. And the most persistent, base notes. Farmstead odors also have top, middle, and base notes. When you still smell hogs on your shirt three days after you worked in a hog barn, those are the base notes hanging on.
- We can arrange our common groups of odorants into top, middle, and base notes of the farmstead odor chord.
- The base notes are made up of the organic acids – the black nasties.
- Earthy smells.
- “ Scat” smells.
- And rotten garbage smells. We give base notes full circles because they last a long time. The colors, of course, refer back to the odorant group.
- Fillers don’t last as long as base notes, so they are thick rings. The middle notes found in farmstead odors are the “green” plant smells.
- The “fishy “nitrogen smells.
- And the “skunky”, cabbagey smells.
- There are only two top notes to speak of in farmstead odors. These are Hydrogen Sulfide – the rotten egg smell.
- And ammonia. Both hydrogen sulfide and ammonia are gases at normal temperatures, and are the only common farmstead odorants that have this distinction. Most odorants are solids at normal temperatures and pressures, and their persistence is related to the volatility -- and to some extent the size -- of the odorant molecule.
- And ammonia. Both hydrogen sulfide and ammonia are gases at normal temperatures, and are the only common farmstead odorants that have this distinction. Most odorants are solids at normal temperatures and pressures, and their persistence is related to the volatility -- and to some extent the size -- of the odorant molecule.
- And ammonia. Both hydrogen sulfide and ammonia are gases at normal temperatures, and are the only common farmstead odorants that have this distinction. Most odorants are solids at normal temperatures and pressures, and their persistence is related to the volatility -- and to some extent the size -- of the odorant molecule.
- Each odorant plays with our senses a little differently. There are two fairly well defined concentrations for every odorant; however, these are the Detection Level and the Recognition Level. The detection level is the concentration at which we can say we smell something, but we cannot describe what it is. At the recognition level, we can not only smell the presence of the odorant, but describe the smell. Let’s use ammonia as an example.
- The recognition level of ammonia is 37,000 parts per billion. When there are 37,000 molecules of ammonia in 1 billion molecules of air, we not only smell something in the room, but we can say that it smells like ammonia window cleaner. Incidentally , 37,000 ppb of ammonia is about the same as 78 gallons (or about a barrel and a half) of pure ammonia gas released into a 400 foot by 40 foot chicken house.
- The recognition level of ammonia is 37,000 parts per billion. When there are 37,000 molecules of ammonia in 1 billion molecules of air, we not only smell something in the room, but we can say that it smells like ammonia window cleaner. Incidentally , 37,000 ppb of ammonia is about the same as 78 gallons (or about a barrel and a half) of pure ammonia gas released into a 400 foot by 40 foot chicken house.
- The detection level of ammonia is only 17 ppb , or about 9 tablespoons of ammonia in a 400 foot by 40 foot poultry building. At this level we can smell something in the building, but we can’t say for certain that it is ammonia. Notice that at this level ammonia is shown as a little speck of blue. This is to represent 17/37,000, or 5 ten thousandths of the blue ring of recognizable ammonia. This is an important concept for agricultural producers to grasp. Sometimes the gases we can’t describe are actually hurting us.
- The detection level of ammonia is only 17 ppb , or about 9 tablespoons of ammonia in a 400 foot by 40 foot poultry building. At this level we can smell something in the building, but we can’t say for certain that it is ammonia. Notice that at this level ammonia is shown as a little speck of blue. This is to represent 17/37,000, or 5 ten thousandths of the blue ring of recognizable ammonia. This is an important concept for agricultural producers to grasp. Sometimes the gases we can’t describe are actually hurting us.
- The acute hazard concentration of ammonia, the point at which your lungs start burning, your eyes start watering, and you begin to cough uncontrollably is 50,000 ppb – well over the recognition level of ammonia.
- The chronic exposure level of ammonia, the concentration at which the every day exposure to ammonia can lead to health problems such as environmentally induced asthma, is 25,000 ppb – below the recognition level of ammonia. So, even if you can’t recognize the smell of ammonia in a poultry house, it can still affect your health. If you can recognize ammonia in your poultry building, it’s way past the time to increase the ventilation rate.
- Let’s look at an example of how an olfactory panel measures odor concentration . The units of odor concentration are Odor Units or OU’s. In Europe, concentration is measured in OU/m 3 or “Odor units per cubic meter.” In North America, it is usually just OU.
- The most common method of measuring odors is Olfactometry. The meaning of the word Olfactometry is “measurement of smells”.
- After an example or two, you will see that this saying is at least a little true. No two people sense an odor the same way, but by sampling many people, we can get a sense of how the majority of people feel about a given smell.
- Olfactometry uses a panel of humans to sense odors delivered by a machine called an olfactometer.
- There are many models of olfactometers, but every one does pretty much the same thing. They deliver precise dilutions of collected odors to an odor panel.
- These are the guts and schematics of a number of olfactometers. There is a source of odorless air, a source of sampled odor, and a method of delivering various combinations of the sampled and odorless air to a panel.
- Remember, an odor is a mixture, or a chord, of odor notes, and notes are composed of individual odor causing chemicals called odorants. In real life, odors are not the simple chord of notes shown here. Farmstead odors are much more complex mixtures.
- This is a fairly accurate visualization of a farmstead odor . It’s not so much a chord as a scream. Scientists in Germany (Hartung J. and V.R. Phillips. 1994. Control of gaseous emissions from livestock buildings and manure stores. J. Ag Eng Res . 57:173) gathered a volume of air from under the slats of a swine manure storage pit, and analyzed the sample for known manure odorants. Their results are represented in the character-persistence-detection-recognition scheme discussed in am earlier part of this series. You can probably see a few bright red rings of hydrogen sulfide, and blue rings of ammonia in this cacophony of odors, but if this was presented undiluted to an olfactory panel, they probably could not distinguish the individual smells of rotten egg or ammonia. They would most likely perceive this as the overwhelming smell of pig.
- The olfactometer dilutes the sample and presents it to the panel at tolerable levels. This is a one in ten dilution of the original sample. All the symbols in the previous slide are divided by ten. A olfactory panel would still say this smelled like pig. If they sniffed it long enough, some might describe the sparkling top notes of ammonia, followed by fishy and plant odors, tapering to the earthy, piggy smell of “scat”
- The panel is then given a blank of odorless air to regain their senses.
- Followed by another dilution.
- And another blank.
- Then one more dilution.
- And a blank. By now you should be seeing a pattern….
- The panel is presented with various dilutions of odors.
- Followed by blanks
- Until the panel can no longer “smell anything”
- Only, the dilutions are given in random order, not the constantly decreasing concentrations you are experiencing.
- Once more than 50% (or a majority) of the panelists.
- Can no longer “detect” an odor.
- They say the odor has reached “dilution to threshold”.
- In classroom situations, I show these dilutions on the screen and ask for a show of hands to indicate if the class can see “anything” on the screen.
- When half of the class cannot see anything.
- We declare that we have reached the dilution to threshold of the original sample.
- Let’s say that dilution to threshold in this example is 1/16,000
- That means, at a dilution of 1/32,000’ 51% or more of the class can no longer see the colored specks on the screen.
- And a majority of the class could see spots at the 1/16,000 dilution. Dilution to threshold is similar to detection threshold of odorants. At this dilution, a majority of the panel could smell “something” in the sample, but they could not describe it is as hog scent.
- Concentration in Odor Units is the inverse of dilution to threshold.
- So, in our case, if dilution to threshold is a one in 16 thousand dilution.
- The inverse is 16,000.
- And the original sample had a concentration of 16,00 odor units.
- Concentration in OU is useful, because the concentration at the source can be plugged into dispersion models, which estimate OU at various spots in the landscape. This doesn’t mean that the modeler can tell you “how” or even “how strong” the dispersed odor “smells” at any point. To answer those questions, you need to measure the intensity and character of the odor.
- The strength or intensity of an odor is measured two different ways. Using a referencing or a descriptive method.
- Butanol is an alcohol. So, in keeping with our color and shape scheme, we say it is a green note. Although, if you were to smell 1-Butanol, you would probably not describe it as “plant-like”.
- Panelists are given the opportunity of sniffing a number of ports on an olfactometer. Commonly, eight ports are used.
- This is a fairly typical result for 12 different people all smelling the same sample. Port 4 was chosen as the port of equal strength by more people than the others, but there is a fairly wide range of opinion, and port 4 was not even chosen by the majority of panelists.
- The second method, or descriptive scale odor intensity is more straight forward. The panelists give direct opinions on the strength of the sample without comparing to any other smells.
- Humans perceive the strength of an odor, not the concentration. However, intensity is related to concentration of odorants in the air.
- The results shown here are from a olfactometry study of swine manure odors conducted in England in the 1990’s. The relationship shown is fairly common. Odor intensity (in this experiment measured by descriptive scale method) is linearly related to the base 10 log of odor concentration . Another way of putting this is, for every increase in odor intensity, there is a 10 fold increase in odor concentration. Referencing suprathreshold odor intensity follows the same pattern. For every 10 fold increase in odorants in a sample, we can expect a 1 point increase in intensity measured as the log base 10 1-butanol concentration. This also explains why the logarithmic transformation of the data is used in the standard method.
- Offensiveness is usually measured using a descriptive scale. And, many times we use offensiveness to compare odors to each other. The first step is to dilute all samples in a sniffing session to the same level of intensity.
- The panel rates the odors on a numeric scale.
- Humans perceive the strength of an odor, not the concentration. However, intensity is related to concentration of odorants in the air.
- Offensiveness is considered an intrinsic property of an odor. A strong smelling skunk doesn’t smell any skunkier than a weak smelling skunk. Only, he’s a stronger smelling skunky skunk.
- Offensiveness is considered an intrinsic property of an odor. A strong smelling skunk doesn’t smell any skunkier than a weak smelling skunk. Only, he’s a stronger smelling skunky skunk.
- Before the lab begins, inform students of the proper procedures for sniffing the samples: Open the sample bottle, wave smells towards the face, and close the bottle afterwards. Do not stick the nose directly into the sample bottle.
- Have the students rate both intensity and offensiveness at the same time. Tell them not to think too hard. Just write down what comes to mind.
- The exercise uses a descriptive scale for both intensity.
- A common scale rates the strength at seven levels. From 0 -- the panelist cannot smell anything to 6 -- the panelist cannot imagine anything possibly smelling stronger.
- A few procedures should be followed to ensure unbiased results. Students should be sent one by one to a separate room to sample the smells. They should not be allowed contact with any other students while entering or leaving the test room.
- And Offensiveness.
- A common scale ranges from 0 to 6, and has descriptions similar to the intensity scale. Zero means that the odor is inoffensive. Inoffensive could mean the odor does not smell bad. It could even smell good. Six means the panelist cannot imagine anything smelling worse than the sample --- knock a buzzard off a gut wagon bad.
- Students should score their opinion immediately after sniffing each sample.
- Provide a can for each smell to collect opinions from the class as a whole.