odors are temporal and spatially dimensioned and can be considered
to be one of the most diffi cult challenges for scientists to investigate. A person’s
response to an odor is highly subjective: different people fi nd different odors
offensive and at different concentrations given that physiologically odor recognition
is associated with the emotional center of brain. Furthermore, some of the
odorous compounds can be detected by the human nose in very low concentrations
(e.g., hydrogen sulfi de) while others cannot be detected even at very high
concentrations (e.g., methane). This is further complicated by the fact that some
combinations of compounds may be more odorous than the sum of the individual
gases. Determining the impact area of odorous gases also is very diffi cult.
As wind direction and speed change, the odor impact area and intensity change.
Depending on specifi c conditions, odorous gases can travel several meters or
several kilometers. Gas transmission and impact area also depend on the specifi c
gas. For these reasons, there is no universally accepted method for the quanti-
fi cation of odors, and odor measurement often has been regarded as an art as
opposed to a science