Odor - The Electronic Nose Artificial Olfaction Technology - page 102

For identified composite, the odor strength can be reliably estimated by mea-
suring the concentration of the chemical, but, for mixtures of unknown substances,
sensory method is preferred.
Measurement of odor is identical for source emission air samples and for
ambient air at the property line and in the community. For determining criteria of
odor limits three basic odor limits built-in for conformity:
1. Ambient odor concentration limits
2. Ambient odor intensity limits
3. Source emission odor concentration limits.
Measuring odor can be accomplished in a number of ways: instrumental methods/
chemical analysis, electronic methods, and sensory test methods/olfactometry.
4.8.1 Instrumental Methods
Mainly instrumental methods available depend on the application of gas chro-
matography (GC), including gas chromatography-mass spectrometry (GC-MS),
since this prime separation technology is competent to the efficient separation
required for analysis of complex mixtures of odor. A mixture of volatile sub-
stances is injected into a column of gas chromatography, which separates the
compounds based on their relative vapor pressures and polarities. The compounds
are then detected as highest point, which have specific maintenance times and
maximum areas, which can be used for qualitative and quantitative determinations,
respectively [ 20 ].
4.8.2 Sensory Methods (Olfactometry)
Measuring odor using the human sense of smell (Olfactometry) is the most valid
way of measuring odor. Accurate measurement of odorous compounds and odor
impact have been challenging because these compounds acquire generally varying
physical and chemical properties and are present at concentrations ranging from
high parts per million (ppm) to low parts per billion (ppb). Olfactometry is the
most commonly used method to measure the concentration of odor in air. Olfac-
tometry is carried out using an instrument called an olfactometer.
Furthermore, each odorant has a unique odor and odor detection threshold
which means that compounds, even if present at the same concentration, may have
markedly different odor impacts. The sensory methods used for measuring odor
level include [ 20 ]: