Making Sense of Smells A Guide for Understanding Farmstead Odors Douglas W. Hamilton Waste Management Specialist Biosystems and Agricultural Engineering Making Sense of Smells A Guide for Understanding Farmstead Odors Part 4: Odor Concentration by Olfactometry

Measuring Farmstead Odors Notes Odors Character Verbal Description Persistence Top Note Middle Note Base Note Concentration Detection Level Recognition Level Intensity In previous segment of this series, we have discussed how individual odor notes are measured. Now we turn to odors, the complex mixtures of many notes.

Olfactometry www2.dpi.qld.gov.au/environment The most common method of measuring odors is Olfactometry. The meaning of the word Olfactometry is “measurement of smells”.

Olfactometry Choosing presidents and measuring odors are very similar processes. OPINIONS ARE IMPORTANT and the majority rules. 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.

Olfactory Panel www2.dpi.qld.gov.au/environment Olfactometry uses a panel of humans to sense odors delivered by a machine called an olfactometer.

Olfactometers www.research-in-germany.de 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. St Croix Sensory www.rka-inc.com www.aromajet.com

Olfactometer www.med-associates.com 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. www.med-associates.com www.coleparmer.com

Measuring Farmstead Odors Notes Odors Character Verbal Description Persistence Top Note Middle Note Base Note Odor Chord Concentration Detection Level Recognition Level OU Intensity 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/m3 or “Odor units per cubic meter.” In North America, it is usually just OU.

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.

1/10 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.

1/100 Followed by another dilution.

And another blank.

1/200 Then one more dilution.

And a blank. By now you should be seeing a pattern….

1/500 The panel is presented with various dilutions of odors.

Followed by blanks

1/1,000 Until the panel can no longer “smell anything”

Only, the dilutions are given in random order, not the constantly decreasing concentrations you are experiencing.

1/2,000 Once more than 50% (or a majority) of the panelists.

Can no longer “detect” an odor.

1/4,000 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.

1/8,000 When half of the class cannot see anything.

We declare that we have reached the dilution to threshold of the original sample.

1/16,000 Let’s say that dilution to threshold in this example is 1/16,000

1/32,000 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.

1/16,000 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.

1 OU = dilution to threshold Concentration in Odor Units is the inverse of dilution to threshold.

1 OU = 1/16,000 So, in our case, if dilution to threshold is a one in 16 thousand dilution.

OU = 16,000 The inverse is 16,000.

And the original sample had a concentration of 16,00 odor units.

Dispersion Modeling 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. www.odotech.com www.air-dispersion-model.com