2.3. Olfactometric analysis
2.3.1. Triangle odor bag method
Gas samples were sent to the State Environmental Protection
Key Laboratory of Odor in Tianjin for olfactometric analysis.
Measurement was conducted using the triangle odor bag method
according to Chinese regulation Air quality-Determination of
odor-Triangle odor bag method (GB 14675-93). The panel for analysis
consisted of six panelists who passed the selection test. Five
standard odors (b-phenylethanol, Methyl cyclopentenone,
Isovalerate, c-Undecalactone, and 3-Methylindole) were used for
the panel selection (Ueno et al., 2009).
During the olfactometric analysis, the sample for the test was
first injected into one of three bags full of odor-free air in an appropriate
dilution ratio, and then a panelist determined which bag was
odorous. The procedure was repeated at different dilution ratios
(from high to low concentration) until the panelist makes a wrong
answer. The geometric mean of the dilution factors of the last correct
answer and that of the first wrong answer is calculated as the
individual threshold. Odor concentration was then calculated as
the geometric mean of individual thresholds, excluding the minimum
and maximum individual thresholds.