NEVROZ GÖSTERİCİ

MEASUREMENT OF ODOR

ODOR CONCENTRATİON

The measurement of odor concentration is the most widespread method to quantify odors. It is standardized in CEN EN . The method is based on dilution of an odor sample to the odor threshold (the point at which the odor is only perceptible to 50 % of the test panel). The numerical value of the odor concentration is equal to the dilution factor that is necessary to reach the odor threshold. Its unit is the European Odor Unit, OUE. Therefore, the odor concentration at the odor threshold is 1 OUE by definition.

To establish the odor concentration, an olfactometer is used which employs a panel of test persons. A diluted odorous mixture and an odor-free gas (as a reference) are presented from sniffing ports to a group of panelists. In comparing the gases emitted from each port, the panelists are asked to report the presence of odor. The gas-diluting ratio is then decreased by a factor of 1.4 or two (i.e. the concentration is increased accordingly). The panelists are asked to repeat their judgment. This continues for a number of dilution levels. The responses of the panelists over a range of dilution settings are used to calculate the concentration of the odor in terms of European Odor Units (OUE/m3).

Olfactometer

ODOR İNTENSİTY

Odor intensity can be divided into the following categories according to intensity:

0 - no odor1 - very weak (odor threshold)2 - weak3 - distinct4 - strong5 - very strong6 - intolerable

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

HEDONİC ASSESSMENT

Hedonic assessment is the process of scaling odors on a scale ranging from extremely unpleasant via neutral up to extremely pleasant. There is no correlation between this method and the method of measuring the odor intensity. However, the hedonic perception of some odors may change from pleasant to unpleasant with increasing concentration and intensity.

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.

EMİSSİON MEASUREMENT

The following details have to be differentiated while the emission is measured:1st 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).

SAMPLİNG TECHNİQUEThere 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 panel 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, where 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 where the odor panel sits. This can sometimes be on the other side of the factory plant. The sample then must therefore pass through 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:

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

High temperatures and moisture content:

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 is true when sampling in high moisture conditions. A way round the problem is to use a stack dilution probe through 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.

High lethal gas concentrations:

Sometimes odor sources emit a high concentration of gases 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.

Odor concentrations:More often than not, odor sampled at the source is higher than 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.

Large odor emitting surface (land or 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 known 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 through which the factories waste air is pumped), a section can be cornered off with plastic (e.g. Teflon) (of which the dimensions are known). 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.

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