Dictionary Definition
aroma
Noun
1 any property detected by the olfactory system
[syn: olfactory
property, smell,
odor, odour, scent]
User Contributed Dictionary
English
Usage notes
The word aroma is usually used to describe a smell favorably and in a positive sense.Synonyms
- italbrac a pleasant smell: fragrance, scent
Translations
a pleasant smell
Related terms
Italian
Pronunciation
Derived terms
Spanish
Noun
Extensive Definition
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. 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. In
contrast, stench, reek, and stink are used specifically to describe
unpleasant odor.
Basics
Odor is a sensation caused by odorant molecules dissolved in the air.
The widest range of odors consist of organic
compounds, although some inorganic substances, such as
hydrogen
sulfide and ammonia,
are also odorants. 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. While odor feelings are very
personal perceptions, individual
reactions are related to gender, age, state of health, and
private affectations. 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.
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.
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.
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.
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. 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. 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
- 1 - very weak (odor threshold)
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. 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
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. 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: ;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.;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. 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. Since that time, the following laws had been made:- “refinery guideline” (early 1970s)
- federal emission protection law (1974)
- technical guideline to keep the air fresh
- 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.
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. 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.
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. 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. The type of
force driving the adsorption process is different between the
two.
Physisorption
A special type of adsorption is physisorption. 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. “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 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. 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. Such interactions could be defined as
a chemisorption because of their strength.
Chemisorption
In many reactions, physisorption is a pre-cursor
to chemisorption. Compared to physisorption, chemisorption is not
reversible and
requires a larger activation energy. 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. 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). 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 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.
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.
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. 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 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.
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. According to a 2006 study 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. 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 female
moth may release a
pheromone that can entice a male moth that is several kilometers
away. Honeybee queens
constantly release pheromones that regulate the activity of the
hive. 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.
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. 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. Many current
electronic nose instruments suffer from problems with
reproducibility with varying ambient temperature and humidity.
External links
References
aroma in Asturian: Golor
aroma in Catalan: Olor
aroma in Czech: Vůně
aroma in Danish: Lugt
aroma in German: Geruch
aroma in Spanish: Olor
aroma in French: Odeur
aroma in Croatian: Miris
aroma in Indonesian: Bau
aroma in Italian: Odore
aroma in Hebrew: ריח
aroma in Lithuanian: Kvapas
aroma in Dutch: Geur
aroma in Japanese: 悪臭
aroma in Uzbek: Hid
aroma in Polish: Zapach
aroma in Portuguese: Odor
aroma in Romanian: Miros
aroma in Russian: Запах
aroma in Serbian: Мирис
aroma in Turkish: Koku
aroma in Ukrainian: Запах
aroma in Chinese: 氣味
Synonyms, Antonyms and Related Words
atmosphere, attribute, aura, badge, balm, balminess, bouquet, brand, breath, cachet, cast, character, characteristic, configuration, cut, definite odor, detectable odor,
differentia,
differential,
distinctive feature, earmark, effluvium, emanation, essence, exhalation, feature, fetor, figure, flavor, fragrance, fragrancy, fruitiness, fume, gust, hallmark, hint, idiocrasy, idiosyncrasy, impress, impression, incense, index, individualism, keynote, lineaments, mannerism, mark, marking, mephitis, mold, muskiness, nature, nosegay, odor, particularity, peculiarity, perfume, property, quality, quirk, redolence, reek, savor, scent, seal, shape, singularity, smack, smell, specialty, spice, spiciness, spoor, stamp, stench, stink, subtle odor, suggestion, sweet savor,
sweet smell, taint,
tang, taste, token, trace, trail, trait, trick, whiff