| Odours |
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What are Odours?Odours are defined (1) as the resulting sensation of the reception on a stimulus by the olfactory sensory system. The way the human respond to an odours stimulus depends on the sensory properties of them in particular, Odour Concentration, Intensity, Quality and Hedonic Tone. The combined effect of these properties is related with the degree of annoyance that an odour can cause. Odour ConcentrationFollowing the European UNE EN 13725 Norm, Odour Concentration is "the number of European odour units in a cubic metre of gas at standard conditions". Therefore the odour concentration is measured in "European Odour Units" and its symbol is uoE (note that the "E" is a subindex). In short, Odour Units works for "odours" as Decybels for "noise". In general, odour unit is calculated from the number of times that a gas sample has to be diluted in order to be detected by a percentage of 50% of a group of people adequately trained for this purpose (pannel). A simple example will show us how to calculate the odour concentration. Supposed that we have taken a bag with odours from some place. If we dilute this sample 1000000 times with odourless air (or nitrogen), it is probable that when the diluted sample is presented to a group of, let's say six people, none of them will detect the odour. If we dilute step by step the "odorous sample" with a smaller concentration of odourless air, there will be a point when half of the people will say that the do detect the odour, and the other half will say that they don't. In this way, if the sample has been diluted 30 times in this time, it is concluded that the odour concentration of the original sample was 30 Odour Units. The measured values depend, of course, on the kind of sensory test, the selection of the panel, the criteria of detectability and other factors. Odour IntensityIn fact, Odour concentration does not inform about how strong is an odour perceived. In contrast, odour intensity does bring information about the degree of annoyance of an odour, that is, odour intensity express the strenth of the odour sensation. Let´s suppose using another example that we could measure a sample of odour collected from the vicinity of a restaurant. If we got a concentration of, let's say 10 ouE. ¿Does this mean that the annoyance perceived by the neighbours is 10 times higher than when there is no restaurant? The answer is NO. Unfortunately, the "Concentration" magnitude is not lineal and depends on many factors. An odour can remain undetected above a certain concentration, its composition may have alterations, its hedonic tone could change from an "annoying odour" at low concentration, to a "pleasant odour" at higher concentration (or the opposite), or it could be perceived with the same degree of annoyance with 2 ouE or with 15 ouE. Odour intensity is the strength of the perceived odour sensation and in many cases It is related with the concentration of an odorous substance. The following equation could define the relation between Odour intensity (I) and concentration (C). “K” is a constant and “n” is the exponent.
Also
This is known as Stevens's law or the power law. For odours, n ranges from about 0.2 to 0.8, depending on the odorant. For an odorant with n equal to 0.2, a 10-fold reduction in concentration decreases the perceived intensity by a factor of only 1.6; whereas for an odorant with n equal to 0.8, a 10-fold reduction in concentration lowers the perceived intensity by a factor of 6.3. The dependence can also be described as a theoretically derived logarithmic function according to Weber and Fechner (2):
where C0 is the threshold concentration; and kw is the Weber-Fechner coefficient or Weber ratio. Which one of these 3 equations applies depends on the method used. To this date, no theory has been able to derive the psychophysical relationship from knowledge about the absolute odour threshold of various substances. When immissions are tested on site, odour intensity is determined by means of an odour inspection. Determination by means of olfactometry is performed under the same conditions like those of the odour threshold determination. The method is well described in the VDI Guidelines 3881 sheet 1-4 and 3882 sheet 1. (4) The following table illustrates the different levels of intensity that can be registered in a field inspection.
Odour QualityOdour quality or character is that property that identifies an odour and differentiates it from another odour of equal intensity. Basically this parameter provides information about what the substance smells like. The odour character is described by a method known as multidimensional scaling or profiling. In this method, the odour is characterised by either the degree of its similarity to a set of reference odours or the degree to which it matches a scale of various descriptor terms. The result is an odour profile. Odour Hedonic ToneHedonic tone is a property of an odour related to its pleasantness. When the hedonic tone of an odour is evaluated in the neutral context of an olfactometric presentation, the panellist is exposed to a controlled stimulus in terms of intensity and duration. The degree of pleasantness or unpleasantness is determined by each panellist experience and emotional associations (3). A distinction has to be made between the acceptability and the hedonic tone of an odour. When an odour is evaluated in the laboratory for its hedonic tone in the neutral context of an olfactometric presentation, the panellist is exposed to a controlled stimulus in terms of intensity and duration. The degree of pleasantness or unpleasantness is determined by each panellist's experience and emotional associations. Sources:
Comments (4)enfermedades causadas por olores
me gustaria saber que enfermedades causan los malos olores
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październik 14, 2009
enfermedades causadas por olores
Hola,
Hay varios estudios que han estudiado la afección a la salud de la contaminación por olores. Así por ejemplo, el Centro Médico de la Universidad de Duke, en un estudio patrocinado por la Agencia de Protección del Medio Ambiente de Estados Unidos, demostró que los olores de determinadas actividades pueden provocar: •molestias respiratorias (congestión de pecho, falta de aliento, tos, flemas) •problemas gastrointestinales (nausea, vómito, diarrea, perdida de apetito) •irritaciones (ojos rojos, garganta congestionada, boca seca, etc) •efectos psicológicos (ansiedad, insomnio, pérdida de concentración, nerviosismo) •dolores de cabeza •fiebre •fatiga. Hay muchos estudios sobre el tema vienen aquí algunas referencias: Steinheider. B. Environmental odours and somatic complaints. Zentralbl Htg Umweltmed, 1999. Sucker et al. Adverse effects of environmental odours: Reviewing studies on annoyance responses and symptom reporting. Water. Sci. Technol, 2001 Rethage et. al., Körperliche Beschwerden im zusammenhang mit Geruchsbelästigungen im Wohnumfeld. Perspektiven fÜr eine systematische, effektive Erfassung, VDI, Gerüche in der Umwelt 2007. Hay muchas más, puede buscarlas a partir de las referencias tomadas por estos artículos. Espero que le sea de ayuda y saludos.
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październik 15, 2009
determinacion de olor en aceites
en los aceites vegetales tienen un compuesto (metilnonilcetona) que le da el olor caracteristico a este aceite de coco. Entonces yo lo paso a una torre de desodorizacion para eliminar este compuesto. Como hago para corroborar que la muestra queda sin olor? Hay una tecnica de laboratorio? Para La ecuacion de Stevens, cual seria la constante? el valor de n entre 0.2 y 0.8 hace refencia a moyor o menor olor? a cual se corresponde? Gracias!
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kwiecień 03, 2010
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