An<unk>  or odour (see spelling differences) is a volatilized chemical compound, generally at a very low concentration, which humans and other animals perceive by the sense of olfaction.  <unk> s are also called smells, which can refer to both pleasant and unpleasant<unk> s.  The terms fragrance, scent, or aroma are used primarily by the food and cosmetic industry to describe a pleasant<unk> , and is sometimes used to refer to perfumes.  In contrast, stench, reek, and stink are used specifically to describe unpleasant<unk> .<unk>  is a sensation caused by<unk> ant molecules dissolved in the air.  The widest range of<unk> s consist of organic compounds, although some inorganic substances, such as hydrogen sulfide and ammonia, are also<unk> ants.  The perception of an<unk>  effect is a two step process.  First, there is the physiological part; the sense of the stimulus by receptors in the nose.  After that, the psychological part follows. The stimuli are processed by the region of the human brain which is responsible for smelling.  Because of this, an objective and analytical measure of<unk>  is impossible.  While<unk>  feelings are very personal perceptions, individual reactions are related to gender, age, state of health, and private affectations. Common<unk> s that people are used to, such as their own body<unk> , are less noticeable to individuals than external or uncommon<unk> s.
For most people, the process of smelling gives little information concerning the ingredients of a substance.  It only offers information related to the emotional impact.  Experienced people, however, such as flavorists and perfumers, can pick out individual chemicals in complex mixes through smell alone.
The concentrations of<unk> ant in Germany have been defined by the “Olfaktometrie” since the 1870’s, which helps to analyze the human sense of smell using the following parameters:<unk>  substance concentration, intensity of<unk> , and hedonism assessment.
To establish the<unk>  concentration, an olfactometer is used which employs a panel of human noses as sensors. In the olfactometry testing procedure, a diluted<unk> ous mixture and an<unk> -free gas (as a reference) are presented separately from sniffing ports to a group of panelists, which are housed in an<unk>  neutral room. They are asked to compare the gases emitted from each sniffing port, after which the panelists are asked to report the presence of<unk>  together with a confidence level such as guessing, inkling, or certainty of their assessment. The gas-diluting ratio is then decreased by a factor of two (i.e. chemical concentration is increased by a factor of two). 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<unk>  in terms of European<unk>  Units (ouE/m³). The main panel calibration gas used is Butan-1-ol., which at a certain diluting gives 1 ouE/m³.
The analytic methods could be subdivided into the physical, the gas chromatographical, and the chemosensory method.
When measuring<unk> , there is a difference between the emission and immission measurements. During the emission measurement, the<unk>  concentration in the air is so high that the so called “Olfaktometer” is needed to thin the assay. Because of this, all measurement methods based on thinning assays are called “olfaktometrical methods.”  On the contrary, an “Olfaktormeter” is seldom used during the immission measurement. The same measuring principals are used, but the judgment of the air assay happens without thinning the assay.
Odor
Itch
Flame
Torque
Heave
Rape
Boil
Wheeze