Is there a measurement scale for how bad something smells?

Question

Sounds have the decibel scale. Light has lumens, watts, candle-power. Earthquakes have the Richter scale. Hurricanes have categories. Etc.

Is there anything for smell?

If there isn't a scale, how would you make one?

For example:

+10 = Sweet
+ 5 = Yum
- 5 = Gross
-10 = Rank

Answer 1

While no generally acceptable method for measuring odor exists, measurement of different aspects of odor can be attempted through a number of quantitative methods, for example:


Odorant concentration

This is the oldest method to define odor emission. Ledger of this method is the concentration of odor substrate at the odor threshold. This threshold is also called apperception barrier. The threshold has got an odorant concentration of 1 GEE/m³ and is subscribed with cod. To define the odorant concentration, it is necessary to dilute the air assay to the odor threshold with the help of the “Olfaktormeter.” The dilution factor Z, at the odor barrier, is the same number as the odor substance concentration.

The European Union has with the introduction of the following standard: CEN EN 13725:2003, Air quality - Determination of odour concentration by dynamic olfactometry. standardized the odor concentration across Europe and odor concentration is now expressed in European Odor Units (ouE/m³).


Odor intensity

This applies a scale to a special air array according to intensity. The scale is differentiated into the following steps:

0 - no odor
1 - very weak (odor threshold)
2 - weak
3 - obvious
4 - strong
5 - very strong
6 - intolerable

If it is an emission measurement (diluted by the olfactometer), then the evaluation of odor intensity must be ranked to the olfactometry methods. A direct evaluation is used, when the array is measured from the emission side.

This method is most often applied by having a dilution series tested by a panel of independent observers who have been trained to differentiate intensity.


Hedonic assessment

The hedonic assessment is the process of scaling odors beginning with extremely unpleasant followed by neutral up to extremely pleasant. There is no difference between this process and the method of measuring the odor intensity. But the method of emission measurement is seldom used and that of emission measurement is not used.


Odor type

This is a verbal characterization of the sensed odor by the test person, such as disgusting, caustic, ruffling, etc. There are no more applications needed than a test person to run this method. The evaluation of the odor type could be an emission or an immission method. It has a great impact on evaluating the source of the odor emission.


Emission measurement

The following details have to be diffetentiated while the emission is measured:

First there is the odor time slice (Result = Part of “odor hours per year” per area). Then there is the olfactory flag scope (Result = Current scope at actual meteorology situation). And last but not least there is the harassment exaltation by questionings (Result = differentiated acquisition harassments).


Sampling technique

There are two main odor sampling techniques, the direct odor sampling and the indirect odor sampling technique.

Direct odor sampling.

Air will be sampled at the source and fed straight into the olfactometer for assessment by an odor panel. The following problems can be associated with this technique:
Odor pannel members need to be seated in an odor neutral environment, thus they need to be housed in a separate area. This is difficult to achieve when assessing odor released from, for example factories, were the odor can be emitted from a stack on the end of a production line. This means that the odor sample collected needs to be transported from the stack to the unit were the odor panel sits. This can sometimes be on the other side of the factory plant. The sample then must therefore pass trough a very long sample line to the olfactometer. This can have influences on the sample quality, can have potential air blockages due to water condensation or other operational procedures. Therefore most odor annoyance assessment companies use the indirect air sampling method.

Indirect odor sampling

Indirect odor sampling is done with the use of odor (air) sampling bags, which are made from an odor neutral material e.g. Teflon. The odor sample bags are connected to an air sampling line which is then, for example, hooked up to a stack. The air stream is then sampled and stored in the odor sample bag and can then be analyzed in a suitable environment (e.g. in an odor laboratory).

The indirect method is used to sample a wide variety of odor sources. From stacks on the end of a factory line, water surfaces or ambient air surroundings.

Each odor source has its own set of problems when sampled; these problems need to be overcome in order to collect a representative sample of the odor source. The following problems can be encountered:

Vacuum.
High temperatures and moisture content.
High lethal gas concentrations.
Odor concentrations.
Large odor emitting surface (land or water).

1) Vacuum

Vacuum can be overcome by placing the odor sample bag in vacuum container which can be placed under vacuum. If the vacuum is higher then the vacuum at the source, the odor sample will collect in the bag.

2) High temperatures and high moisture contents

High temperatures and high moisture contents inside the odor source leads to complications when sampled. When the sample leaves the source, it will cool down and produce condensate in the sample line and or odor sample bag. This can lead to growth of bacteria or when drying out release more odor, thus alter the odor concentration of the sample. The same hold up when sampling in high moisture conditions. A way round the problem is to use a stack dilution probe trough which an inert gas (for example dry nitrogen) can be fed that dries the sample stream. This prevents the moisture condensing in the sample line and or the odor sample bag.

3) High lethal gas concentrations

Sometimes odor sources emits a high concentration of gasses that are lethal to man. These samples must be diluted to a safe level, before being presented to the odor panel. This pre-dilution can be done in a stack-dilution probe, by the addition of an inert gas or on a dilution device for example an extra olfactometer.

4) Odor concentration

More often than not, odor sampled at the source is higher then the ambient odor concentration. In a few cases the odor concentration can be so high that panelists will make a positive identification even if the olfactometer is diluting the odor sample in its upper dilution range. The sample must then be pre-diluted to make a sensible reading, this pre-dilution can again be done with a stack-dilution probe, by the addition of an inert gas or on a dilution device for example an extra olfactometer.

5) Large odor emitting surface (land or on water).

When a large surface is emitting odor, for example a sewage treatment plant, a fixed dimension “hood” can be used. In one end of the hood, clean air is blown in at a know rate, and on the other end, a sample is collected via the indirect method. If a large land surface is emitting odor, for example a bio filter (a big concrete basin filled with wood chip trough which the factories waste air is pumped), a section can be cornered off with plastic (e.g. Teflon) (of which the dimensions are know). The air from the factory will inflate the plastic (lift it up) and an odor sample can be taken from under the plastic via the direct air method.

All involved sampling parts have to be made out of olfactory neutral materials. Principally every sampling has to meet the logically requirements, has to be defined, standardized, meaningful and reproducible. This is needed to make different measurements comparable. Odorant concentrations scaled in either GG/m³ or ouE/m³ aren’t convincing while comparing different emissions of different plants. Because of this instead of comparing different concentrations, different emission mass currents of the emitted freight are compared.

Answer 2

there's already been a recent nobel prize for this sort of thing....
You're clearly on the level of the nose-genius, but they've beat ya to it.

Answer 3

How fast and far you run and how loud you scream while you try to get away from it.