A comparative analysis of malodor samples between direct (olfactometry) and indirect (instrumental) methods

The relationship between direct (olfactometry) and indirect (instrumental) methods for odor detection was assessed using a total of 70 odor samples collected from several industrial sectors. To this end, a number of instrumental techniques have been employed to measure the concentrations of major odorant groups, including reduced sulfur compounds (RSC), volatile organic compounds (VOC), aldehydes, and nitrogenous compounds. The odorant data obtained by the indirect methods were then converted into the following three modified odor indices: (1) the (algebraic) sum of odor concentration (SOC), (2) the sum of odor quotient (SOQ) by considering the relation between odorant concentration and threshold value, and (3) the sum of odor intensity (SOI) based on suprathreshold olfactometry. These derivatized indices were then compared against the results of the direct method, i.e., dilution to the threshold (D/T) ratio via olfactometry such as air dilution sensory (ADS) test. When the relationship was investigated between D/T ratios and those three derivatized indices, the results of 70 samples were strongly correlated with the Pearson coefficients (r) of 0.671 for SOC (P=1.92E−10), 0.866 for SOQ (P=2.74E−22), and 0.852 for SOI (P=6.53E−21). It thus confirms that the odorant concentration data measured by instrumental method can be used effectively to account for the odor intensity estimated by the sensory method for samples collected under strong source activities.