An odor 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. The Luna Moth ( Actias luna) is a lime-green, Nearctic Saturniid Moth in the subfamily Saturniinae. American and British English spelling differences are one aspect of American and British English differences. A chemical compound is a substance consisting of two or more different elements chemically bonded together in a fixed proportion by Mass. Senses are the physiological methods of Perception. The senses and their operation classification and theory are overlapping topics studied by a variety of fields Olfaction (also known as olfactics or smell) refers to the Sense of smell. Odors are also called smells, which can refer to both pleasant and unpleasant odors. The terms fragrance, scent, or aroma are used primarily by the food and cosmetic industry to describe a pleasant odor, and are sometimes used to refer to perfumes. Perfume is a mixture of fragrant Essential oils and Aroma compounds Fixatives and Solvents used to give the human body animals objects and living In contrast, stench, reek, and stink are used specifically to describe unpleasant odor.

Contents 1 Basics 2 Odor analysis 3 General survey 4 Measurement 4.1 Odorant concentration 4.2 Odor intensity 4.3 Hedonic assessment 4.4 Odor type 4.5 Emission measurement 4.6 Sampling technique 4.6.1 Direct odor sampling 4.6.2 Indirect odor sampling 5 Legislative provisions associated with odors 6 Adsorption as separating process 6.1 Physisorption 6.2 Chemisorption 6.3 Loading of the adsorben 7 Types of odors 7.1 The study of odors 7.2 Pheromones 7.3 Advanced technology 8 See also 9 External links 10 References

Basics

Odor is a sensation caused by odorant molecules dissolved in the air. In Psychology, sensation is the first stage in the biochemical and neurologic events that begins with the impinging of a stimulus upon the receptor cells of a In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by The widest range of odors consist of organic compounds, although some inorganic substances, such as hydrogen sulfide and ammonia, are also odorants. An organic compound is any member of a large class of Chemical compounds whose Molecules contain Carbon. Traditionally inorganic compounds are considered to be of mineral not biological origin Hydrogen sulfide (or hydrogen sulphide) is the Chemical compound with the formula H 2 S. Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor The perception of an odor 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 odor is impossible. "n objective account is one which attempts to capture the nature of the object studied in a way that does not depend on any features of the particular subject who studies it While odor feelings are very personal perceptions, individual reactions are related to gender, age, state of health, and private affectations. In Psychology and the Cognitive sciences perception is the process of attaining awareness or understanding of sensory Information. Gender comprises a range of differences between men and women extending from the biological to the social Common odors that people are used to, such as their own body odor, are less noticeable to individuals than external or uncommon odors.

For most people, the process of smelling gives little information concerning the ingredients of a substance. This article is about ingredients in general There is also an American soul and R&B group called The Main Ingredient. 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. A flavorist, also known as flavor chemist is someone who uses both Chemistry and art to engineer artificial and natural Flavors The tools and materials used by flavorists The Perfumer is an expert on Perfume composition sometimes referred to affectionately as "the Nose " (french le nez) due to their fine sense of

Odor analysis

In Germany, the concentrations of odorants have since the 1870’s been defined by the “Olfaktometrie”, which helps to analyze the human sense of smell using the following parameters: odor substance concentration, intensity of odor, and hedonic assessment. Germany, officially the Federal Republic of Germany ( ˈbʊndəsʁepuˌbliːk ˈdɔʏtʃlant is a Country in Central Europe.

To establish the odor concentration, an olfactometer is used which employs a panel of human noses as sensors. In the olfactometry testing procedure, a diluted odorous mixture and an odor-free gas (as a reference) are presented separately from sniffing ports to a group of panelists, which are housed in an odor 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 odor 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 odor in terms of European Odor Units (ouE/m³). The main panel calibration gas used is Butan-1-ol. , which at a certain diluting gives 1 ouE/m³.

General survey

The analytic methods could be subdivided into the physical, the gas chromatographical, and the chemosensory method. This page is about the physical properties of gas as a state of matter

When measuring odor, there is a difference between the emission and immission measurements. During the emission measurement, the odor concentration in the air is so high that the so called “Olfaktometer” is needed to thin the assay. An assay is a procedure where a property or concentration of an Analyte is measured Because of this, all measurement methods based on thinning assays are called “olfaktometrical methods. ” On the contrary, an “Olfaktormeter” is rarely used during the immission measurement. The same measuring principals are used, but the judgment of the air assay happens without thinning the assay.

Measurement

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 for defining odor emission. Ledger of this method is the concentration of odor substrate at the odor threshold. This threshold is also called apperception barrier. Apperception (Latin ad + percipere, to perceive has the following meanings In Epistemology, it is "the introspective or reflective 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

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

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 an odor's intensity must be ranked by the olfactometer methods. Evaluation is systematic determination of merit worth and significance of something or someone using criteria against a set of standards 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. Hedonism is the Philosophy that Pleasure is of ultimate importance, the most important pursuit There is no correlation between this process and the method of measuring the odor 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.

Emission measurement

The following details have to be differentiated 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 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 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. Teflon is a Registered trademark and Brand name of the DuPont company for products made from three types of fluorine-containing polymers ( Fluoropolymers 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 then 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 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.

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.

Odor concentrations

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.

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 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.

Legislative provisions associated with odors

When legislation for environmental protection in Germany first began, it raised the question of the evaluation of different odors. Germany, officially the Federal Republic of Germany ( ˈbʊndəsʁepuˌbliːk ˈdɔʏtʃlant is a Country in Central Europe. Since that time, the following laws had been made:

1. “refinery guideline” (early 1970s)
2. federal emission protection law (1974)
3. technical guideline to keep the air fresh
4. olfactory emission guideline (early 1980s until 1998)

Controls at the point of the emission, like plural vitrification against aircraft noise, drop out. Terms of transmission could be marginally changed by establishing ramparts, plantings and so on, but the objective efficiency of those controls is likely minimal. But the subjective efficiency of a plantings is remarkable. Subjectivity refers to a subject's perspective particularly feelings beliefs and desires

The choice of the location is the most important control, that means keeping an adequate distance to the nearest receptor and paying attention to the meteorology conditions, such as the prevailing wind direction. Meteorology (from Greek grc μετέωρος metéōros, "high in the sky" and grc -λογία -logia) is the Interdisciplinary Reduction of the emission, by way of dilution of a small emission concentration with large air flow volumes, could be an effective and economic alternative, instead of reducing the emission with different controls.

Encapsulating of olfactory relevant asset areas is the best known method to reduce the emission, but it is not the most suitable one. Different matters need to be considered by encapsulation. Within an enclosure a damp and oppressive atmosphere can arise, so that the inner materials of the capsule produce a high degree of mechanical stress. An atmosphere (from Greek ατμός - atmos, " Vapor " + σφαίρα - sphaira, " Sphere " Not to let the explosion hazard slide.

For encapsulation to be viable, there must be some way to exhaust the spent air. When emission is avoided through capsuling, odorants remain inside the medium and tend to leak at the next suitable spot. In any case, capsuling is never really gas-proof, and at some spots substances may leak out at considerably higher concentrations.

There are three different ways exhausted air may be treated:

• chemical treatment
• physical treatment
• biological treatment

Adsorption as separating process

Adsorption is a thermo separation process, which is characterized by the removal of molecules out of a fluid phase at a solid surface. Adsorption is a process that occurs when a gas or liquid Solute accumulates on the surface of a solid or a liquid (adsorbent forming a film of molecules or atoms (the In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by Molecules of a gas- or fluid mixture are taken up by a solid with a porous interface surface. The solid matter is called the adsorbant, the adsorbed fluid is called the adsorbate. There are two types of adsorption, physisorption and chemisorption. Physisorption or physical adsorption is a type of Adsorption in which the adsorbate adheres to the surface only through Van der Waals (weak intermolecular interactions Chemisorption is a type of Adsorption whereby a Molecule adheres to a Surface through the formation of a Chemical bond, as opposed to the The type of force driving the adsorption process is different between the two.

Physisorption

Main article: Physisorption

A special type of adsorption is physisorption. Physisorption or physical adsorption is a type of Adsorption in which the adsorbate adheres to the surface only through Van der Waals (weak intermolecular interactions The difference between physisorption and chemisorption is that the adsorbed molecule is tied up with the substrate by physical forces, defined here as forces which doesn’t cause chemical bonds. Such interactions are mostly unfocused in contrast to chemical bonds. A chemical bond is the physical process responsible for the attractive interactions between Atoms and Molecules and which confers stability to diatomic and polyatomic “Van-Der-Waals” – forces are a special type of such physical forces. These forces are characterized by electrostatic interactions between induced, fluctuating dipoles. To be more specific you have to call those forces “London's Dispersal forces”. A so called dipole moment occurs because of fluctuations in the distribution of electrons around individual atoms. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J The temporary mean value of this force is however zero. Even though it’s only a mere transient dipole moment, this moment can cause a nonparallel dipole moment in an adjacent molecule. In physics there are two kinds of dipoles ( Hellènic: di(s- = two- and pòla = pivot hinge An electric dipole is a Operating forces of this nature are in inverse proportion to the sixth power of the distance between those molecules. These forces occur in almost every chemical system, but are relatively weak.

Physisorption is an exothermic and reversible reaction. Obviously stronger strengths accrue through the interaction between solid dipoles at polar surfaces or reflexive loadings, appearing in electric conductive surfaces. A solid' object is in the States of matter characterized by resistance to Deformation and changes of Volume. Such interactions could be defined as a chemisorption because of their strength.

Chemisorption

Main article: Chemisorption

In many reactions, physisorption is a pre-cursor to chemisorption. Chemisorption is a type of Adsorption whereby a Molecule adheres to a Surface through the formation of a Chemical bond, as opposed to the Compared to physisorption, chemisorption is not reversible and requires a larger activation energy. In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός Usually the bond energy is about 800 kJ/mol. For physisorption the bond energy is only about 80 kJ/mol. A monomolecular layer could be maximally adsorbed. Strong bonds between the adsorbative molecules and the substrate could lead to the point that their intermolecular bonds partly or completely detach. In such a case you have to call this a dissociation. Those molecules are in a highly reactive state. This is the basis of heterogeneous catalysis. Heterogeneous catalysis is a Chemistry term which describes Catalysis where the Catalyst is in a different phase (ie The substrate is then called catalytic converter. The differences between Chemisorption and Physisorption extends beyond an increased activation energy. An important criteria for chemisorption is the chemical mutation of the absorbent. Thereby it is possible that you have to deal with a chemisorption in a few combinations with a relatively low bond energy, for example 80 kJ/mol, as a physisorption could be another combination with a bond energy even by 100 kJ/mol. The interaction with different adsorbative molecules is very different. The surface could be taken by substances, which point out a very high bond energy with the substrate, and as a consequence of this the wanted reaction is impossible. Because of that feature those substances are called catalytic converter venom. Heat is released during that process too.

Loading of the adsorben

During the adsorption of a molecule, energy - the heat of adsorption – is released. This energy is the difference of the enthalpy of the adsorben in the fluid or gaseous phase and the its corresponding enthalpy on the surface of the adsorbant. With an increase of the loading on the surface of the adsorbant the bond energy decreases in the area of the monomolecular covering. For higher loading this value approaches zero. This implies that there is a limit for the loading of an adsorbant. The procedure of turning back that process is called desorption. Adsorption as a separating process is a challenging process, in the case of finding the eligible adsorbents, which could link as multilateral as possible.

Types of odors

Some odors such as perfumes and flowers are sought after, elite varieties commanding high prices. Whole industries have developed products to remove unpleasant odors (see deodorant). Deodorants are substances applied to the body particularly the Armpits mainly to reduce Body odor caused by the bacterial breakdown of Perspiration. The perception of odors is also very much dependent upon circumstance and culture. The odor of cooking processes may be pleasurable while cooking but not necessarily after the meal.

The odor molecules send messages to the limbic system, the area of the brain that governs emotional responses. Some believe that these messages have the power to alter moods, evoke distant memories, raise their spirits, and boost self-confidence. This belief has led to the concept of “aromatherapy” wherein fragrances are claimed to cure a wide range of psychological and physical problems. Aromatherapy is a form of Alternative medicine that uses volatile liquid plant materials known as Essential oils (EOs and other aromatic compounds from plants for Aromatherapy claims fragrances can positively affect sleep, stress, alertness, social interaction, and general feelings of well-being. However, the evidence for the effectiveness of aromatherapy consists mostly of anecdotes and lacks controlled scientific studies to back up its claims. The expression anecdotal evidence has two quite distinct meanings Science (from the Latin scientia, meaning " Knowledge " or "knowing" is the effort to discover, and increase human understanding

With some fragrances, such as those found in perfume, scented shampoo, scented deodorant, or similar products, people can be allergic to the ingredients. The reaction, as with other chemical allergies, can be anywhere from a slight headache to anaphylactic shock, which can result in death. Anaphylaxis is an acute systemic (multi-system and severe Type I Hypersensitivity allergic reaction in humans and other Mammals

Unpleasant odors can arise from certain industrial processes, adversely affecting workers and even residents downwind of the industry. The most common sources of industrial odor arise from sewage treatment plants, refineries, certain animal rendering plants and industries processing chemicals (such as sulfur) which have odorous characteristics. Sewage treatment, or domestic wastewater treatment, is the process of removing Contaminants from Wastewater, both Runoff ( Effluents A refinery is composed of a group of Chemical engineering unit processes and Unit operations used for Refining certain materials or converting Sometimes industrial odor sources are the subject of community controversy and scientific analysis.

The study of odors

The study of odors is a growing field but is a complex and difficult one. The human olfactory system can detect many thousands of scents based on only very minute airborne concentrations of a chemical. The Olfactory helps and relates sense of smell. The olfactory system is the Sensory system used for Olfaction. The sense of smell of many animals is even better. Some fragrant flowers give off odor plumes that move downwind and are detectable by bees more than a kilometer away. Honey bees learn and communicate in order to find food sources and for other means Bees are flying Insects closely related to Wasps and Ants Bees are a Monophyletic lineage within the superfamily Apoidea

The study of odors can also get complicated because of the complex chemistry taking place at the moment of a smell sensation. For example iron metal objects are perceived to have an odor when touched although iron vapor pressure is negligible. Vapor pressure (also known as equilibrium vapor pressure or saturation vapor pressure) is the Pressure of a Vapor in equilibrium According to a 2006 study^[1] this smell is the result of aldehydes (for example nonanal) and ketones (example: 1-octen-3-one) released from the human skin on contact with ferrous ions that are formed in the sweat-mediated corrosion of iron. An aldehyde is an organic compound containing a terminal Carbonyl group. Nonanal, also called nonanaldehyde or pelargonaldehyde, is an Alkyl Aldehyde. A ketone (pronounced as key tone) is either the Functional group characterized by a Carbonyl group (O=C linked to two other Carbon atoms or Ferrous, in the chemical science realm indicates a bivalent iron compound (+2 oxidation state (as opposed to Ferric, which indicates a trivalent iron compound (+3 oxidation The same chemicals are also associated with the smell of blood as ferrous iron in blood on skin produces the same reaction.

Pheromones

Pheromones are odors that are deliberately used for communication. A pheromone (from Greek φέρω phero "to bear" + ‘ορμόνη " Hormone " is a Chemical that triggers a natural A female moth may release a pheromone that can entice a male moth that is several kilometers away. A moth is an Insect closely related to the Butterfly, both being of the order Lepidoptera. Honeybee queens constantly release pheromones that regulate the activity of the hive. This article refers collectively to all true honey bees for the "common" domesticated honey bee see European honey bee Honey bees HIVE is an abstract game Programming library. It is designed to be simple and easy to understand Workers can release such smells to call other bees into an appropriate cavity when a swarm moves in or to "sound" an alarm when the hive is threatened.

In mammals some pathway of Pheromones identification lay in vomeronasal organ and some - in odor receptors. Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands The vomeronasal organ ( VNO) or Jacobson's organ, is an auxiliary Olfactory Sense organ that is found in many Animals It was Olfactory receptors expressed in the Cell membranes of Olfactory receptor neurons are responsible for the detection of Odor molecules

Advanced technology

There are hopes that advanced smelling machines could do everything from test perfumes to help detect cancer or explosives by detecting certain scents, but as of yet artificial noses are still problematic. The complex nature of the human nose, its ability to detect even the most subtle of scents, is at the present moment difficult to replicate.

Most artificial or electronic nose instruments work by combining output from an array of non-specific chemical sensors to produce a finger print of whatever volatile chemicals it is exposed to. An electronic nose is a device intended to detect odors or flavors A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument Most electronic noses need to be "trained" to recognize whatever chemicals are of interest for the application in question before it can be used. The training involves exposure to chemicals with the response being recorded and statistically analyzed, often using multivariate analysis and neural network techniques, to "learn" the chemicals. Multivariate analysis (MVA is based on the statistical principle of Multivariate statistics, which involves observation and analysis of more than one statistical variable Traditionally the term neural network had been used to refer to a network or circuit of biological neurons. Many current electronic nose instruments suffer from problems with reproducibility with varying ambient temperature and humidity. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature Humidity is the amount of water vapor in the air In daily language the term "humidity" is normally taken to mean Relative humidity.

See also

• Olfaction
• Aroma compound
• Olfactory fatigue
• Machine olfaction

External links

• Answers to several questions from curious kids about smells and odors

References

Olfaction (also known as olfactics or smell) refers to the Sense of smell. Olfactory fatigue or adaptation is the temporary normal inability to distinguish a particular Odor after a prolonged exposure to that airborne compound Machine olfaction is the automated simulation of the sense of smell Angewandte Chemie is a weekly Peer-reviewed Chemistry journal that covers all disciplines of chemistry A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.

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