代写 DESC9021 Applied Psychophysics
Applied Psychophysics

Focus on Human Factors Underlying
Air Quality and Odour Assessment
(Olfactory Sensation… and More)
Prepared for DESC9021, 2016
by William Martens

Air Quality is not Just About Odour


Everyone is familiar with what happens when onions are chopped…
Air Quality is not Just About Odour
Something similar happens in both the nose and the eyes when they’re exposed to an irritant such as SO2 gas, but what is it that actually triggers the release of the tears?

The answer can be found by looking at the nasal membrane (where chemoreceptors detect both odour and irritation).
The Olfactory Sensory System…   …just detects odour, buy what about feeling?
Sometimes a compound is both an odorant and an irritant: These compounds stimulate both the olfactory sense organ and the common chemical sense
The Olfactory Sense Organ… and More…
Chemesthesis is not just about the response to airborne irritants
Chemesthesis serves for oral sensations as well:
  the burn of chili pepper,
  the coolness of menthol,
  and the tingle of carbonation.

So it’s not just the mucus layer of the nasal membrane that has the  free nerve ending receptors that are responsible for the common chemical sense, it is also the inside of the mouth that allows for sensations of pungency (as distinct from the sense of taste for which only gustatory receptors in the tongue are responsible).

Irritation Grows with Exposure Time
While the irritation gets worse as you chop an onion, the onion odour does not grow stronger:

The perceived magnitude of the onion’s odour is predicted by the concentration of the odorant (i.e., the percentage of odorant molecules entering the nose).

The perceived magnitude of the onion’s pungency is predicted by the number of irritant molecules per unit time during exposure.

This finding underscores the difference between two chemoreceptive modalities, the olfactory sense and the common chemical sense.

So when eating the Korean delicacy called Hongeohoe (fermented skate), the odour of ammonia that you smell when you enter the restaurant never gets stronger, while the pungency grows and grows for the first 10 minutes of waiting for the delicacy to arrive…
It looks appetising!
But can you eat the fermented skate?
Hongeohoe

Speaking of smelly restaurants…
A primary concern in Interior Environmental Quality (IEQ) is the contribution of air quality to what has been termed…

  Sick Building Syndrome

Although this syndrome may have other causes, a common cause is a high concentration of various Volatile Organic Compounds (VOCs), such as the formaldehyde emitted by new carpets, upholstery, and plastic laminate furnishings found in modern office buildings.

Sick Building Syndrome
The Volatile Organic Compounds (VOCs) irritate free nerve endings in exposed mucus membranes (e.g., eyes, nose, throat) causing discomfort and headaches at low concentrations, and potentially causing coughing and tearing at higher concentrations.

Strangely, when the air in “sick” buildings is analysed, there is no single VOC found at high enough concentration to be worrisome, and so complaints are ignored, or merely regarded as excuses for employees to get out of work!

According to Cometto-Muñiz and colleagues, however, when several VOCs are mixed together, the combined result can be well above the threshold for experiencing a strong pungent sensation in the nose, though each VOC alone would go undetected.

Why did it take so long for this fundamental research finding to be applied to practical cases in the built environment?  There was a difficulty that required clever research design.
Studies of Air Quality relating to the Sick Building Syndrome
Initially, studies of the detection of Volatile Organic Compounds (VOCs) mixtures were confounded by the easy detection of the odours of the various component VOCs, this being because the thresholds for detection of odours are often much lower than those for reporting sensations of pungency.

So to avoid this confound, Cometto-Muñiz and Cain (1990) worked with a group of volunteers who were anosmic,  i.e., a group of experimental volunteers who were insensitive to odour.

Threshold VOC concentrations for anosmics were compared to those for a group of volunteers who were normosmic, having normal odour sensitivity.
But first, what modulates odour thresholds?
At the same concentration, different odorants may have very differ strengths.

Consequently, some odours can be detected at extremely low concentrations, while others must be highly concentrated before they are even noticed.

For example, the threshold concentration for detecting the odour of various types of alcohol depends on the chemical structure of the alcohol molecule…



Thresholds for odor and nasal pungency
J.Enrique Cometto-Muñiz , William S. Cain (1990), Physiology & Behavior, 48(5), 719–725.
To summarize:
 Airborne volatiles can provoke two types of sensations in the nose: the first one being sensations of smell, mediated by the olfactory system), and the second one being sensations of irritancy (typically: burning, tingling, or prickling), mediated primarily by the other chemoreceptive modality called the common chemical sense.

Traditionally, the concentration at which individuals start to perceive an odour has been determined using forced-choice threshold detection procedures, but it wasn’t so obvious how to measure detection thresholds for irritation.
Of course,  a compound (such as alcohol), often is both an odorant and an irritant: It stimulates both the olfactory sense organ and the common chemical sense
How to test for irritancy in the context of an odor in normosmics?

A method was developed for determining the threshold for irritancy in the context of an odor (Wysocki, et al, 1997):
Individuals are asked to say whether the irritant is presented to the right or left nostril in a forced-choice procedure in which one irritant stimulus and one blank stimulus are presented simultaneously to either nostril.

This method is based on the principle that volatiles can be lateralized only after detectable peripheral stimulation of the trigeminal nerve (serving the common chemical sense), but not after stimulation of only the olfactory nerve.
How to test for irritancy in the context of ammonia in normosmics

Using the pictured dirhinic stimulator, measured odour detection thresholds for ammonia were 2.6 ppm while lateralization thresholds were 31.7 ppm (parts per million):

10 times more ammonia was needed for just detectable irritation (than just detectable odour).

Smeets, et al (2007) Odor and Irritation Thresholds for Ammonia: A Comparison between Static and Dynamic Olfactometry, Chem. Senses 32: 11–20

Interaction between chemoreceptive modalities of odour and irritation
See:  W.S. Cain, C.L. Murphy (1980), Nature, 284 pp. 255–257
Gender Differences
in the Perception of Pungency
J.Enrique Cometto-Muñiz, Gustavo Noriega (1984), Gender differences in the perception of pungency, Physiology & Behavior, 34(3), 385-389.
Gender Differences
in the Perception of Pungency
J.Enrique Cometto-Muñiz, Gustavo Noriega (1984), Gender differences in the perception of pungency, Physiology & Behavior, 34(3), 385-389.
Gender Differences
in the Perception of Pungency
J.Enrique Cometto-Muñiz, Gustavo Noriega (1984), Gender differences in the perception of pungency, Physiology & Behavior, 34(3), 385-389.
Gender Differences in Odour Identification
Cain (1982), asked more than 200 males and females to identify 80 common odorous objects (e.g., chocolate, beer, mustard, rubber).
Both groups anticipated that males would be superior for only a small number of substances, mainly substances that seem stereotypically ‘male’ (e.g., cigar butts, beer, machine oil).
The groups anticipated female superiority for not only stereotypically ‘female’ substances (e.g., Ivory soap, Johnson's baby powder, nail polish remover), but also for virtually all foods, including foods presumably consumed equally by both sexes (e.g., potato chips, Juicy Fruit gum, grape drink).
The results suggested the existence of a simpler stereotype, namely that females will be superior at identifying all substances not clearly in the male domain. An experiment that explored the performance of 46 males and females over five sessions revealed general female superiority. The superiority extended to odors considered ‘male’.
Gender Differences in Odour Identification
Odor Identification
Odor Identification
Gender Identification from Human Breath Odor?
Gender Recognition from Human Breath Odor?
Yes, that was Hydrogen Sulfide
The breath of the human male contains more hydrogen sulfide (H2S) than does the breath of the human female…
   …enough for the H2S ‘rotten egg’ odour to be detected easily!

  As far as common noxious gases are concerned, only the putrid odour of   methyl mercaptan is worse (more like rotten cabbage than like rotten eggs).

Odour Thresholds
Hydrogen Sulfide Odour
The largest industrial source of H2S is petroleum refineries; however, ordinary citizens can be exposed to hydrogen sulfide by being near landfills, waste water treatment facilities, and farms with manure storage.

Although hydrogen sulfide (H2S) is found in crude petroleum, volcanoes and some hot springs can produce enough for the odour to be quite strong…

And yet, this odour can grow on you if you enjoy soaking in the natural hot springs of a Japanese mountain retreat, such as the Higashiyama Onsen (pictured in the next slide).
代写 DESC9021 Applied Psychophysics


Odour Impact Assessment Handbook
For further reading on the practical evaluation of odour and assessment of its impact, please see he handbook with this title (from which a number of figures shown in this lecture were taken):

Editors: Belgiorno, Vincenzo, Naddeo, Vincenzo, and Zarra, Tiziano.
New York : Wiley, 2012.  
ISBN 9781118481288

You can connect to fulltext via EBL (through the University of Sydney Library’s online catalogue).
Questions about Odour?
代写 DESC9021 Applied Psychophysics