ENV 3A08
Odour, being a subjective parameter, cannot be measured directly, by chemical techniques, so "strength of odour" is usually determined measured by diluting the odour with clean air until half the chooses test panel can no longer perceive the odour (eg Frechen, 1992), or through test panels actually working in the field. Odour problems can often possess a transitory nature that makes abatement difficult, yet this is frequently the major interest of those who deal with these issues at an administrative level.
Although odour may be associated with compounds that might be regarded as non-toxic, noxious environmental odours can trigger symptoms through a variety physiological mechanisms including exacerbation of underlying medical conditions, innate odour aversions, stress induced illness and possible pheromonal interactions. Patterns of subjective responses of those living close to environmental odours are well known, but objective correlations between odour and the symptoms are as yet indeterminable (Shusterman, 1992).
FLOWERY FRUITY
PUTRID
and on the bottom:
SPICY RESINOUS
BURNT
Each distinct odours is aid to be describe by a point within this prism. However the scheme is still inadequate, and many other systems with special relevance to perfumery, botany &tc have been developed.
The Henning system does not appear particularly good for urban odour and air pollution science appears in need of a good system of odour description.
ODOUR INTENSITY As with many human sensory experiences, intensity (I) is related to a power function of the stimulus, in the case of odour this would be the olfactant concentration (C):
I = kCn
where k is a constant and n tends to lie in the range 0.2-0.8 for the sensation of smell (eg butanol 0.63, propanoic acid 0.42, acetophenone, 0.45).
For odour surveys a scale of 0-5 is often used (eg Dravnieks, 1972) and here we have adapted it a little for the current experiment by adding a sense of whether the odour is continuous or not:
0 non-existent
1 barely perceptible and exceedingly fragmentary
2 faint and fragmentary
3 easily noticeable
4 strong and fairly persistent
5 very strong and persistent
Over time our sense of smell weakens through a sort of anaesthetic effect.
(ii) determine the distribution of odour within the city
(iii) consider the relevance and offensiveness of odour in modern cities
Hand sheets into to the demonstrator when you return to the bus. The results will be analysed in a later practical session.
a 0 non-existent: 1 barely perceptible and exceedingly fragmentary, 2 faint and fragmentary, 3 easily noticeable, 4 strong and fairly persistent, 5 very strong and persistent.
b Class: 1 Burnt-Acrid-Smokey, 2 Fuelly, 3 Solventy, 4 Floral-Fruity, 5 Putrid-Fishy-Earthy, 6 "Foody"
Dravnieks, A, Interfacing of sensory and analytical measurements, in Mamantov, G & Shults, WD Determination of Air Quality, Plenum Press, NY 1972, 163-178.
Frechen, FB, Odor emissions of large WWTP'S - source strength measurement, atmospheric dispersion calculation, emission prognosis, Countermeasures - case-studies, Water Science and Technology 1992 vol.25 no.4-5 pp.375-382.
R. Harper, E.C. Bate Smith and D.G. Land, Odour description and odour classification a multidisciplinary examination, London ; J. & A. Churchill, 1968. Henning, H. Der Geruch I, Zeit. fur Psychologie und Physiologie der Sinnesorgane, 1915, 73, 161.
Shusterman, D, Critical-review - the health significance of environmental odor pollution, Archives of Environmental Health 1992 vol.47 no.1 pp.76-87.
Walter, S. Odour pollution of air causes and control, London ; L. Hill, 1971.