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CORRELATION OF HUMAN ODOR RESPONSE MAGNITUDES TO AIR CONCENTRATIONS OF MALODOROUS VOLATILE ORGANIC COMPOUNDS ASSOCIATED WITH SWINE MANURE ODOR
Anaerobic processing of livestock wastes results in the production of air pollutants including volatile organic compounds (VOCs), methane, hydrogen sulfide, ammonia, and odors. Quantification of odor and trace gases from animal production facilities have traditionally been addressed
in separate, unrelated research efforts due to analytical difficulties associated with the measurement of low concentrations of analytes in air samples. As a result, there is currently a lack of information concerning the ambient air concentration range and chemical identity of odorant compounds
released from stored animal manure. This lack of information has impeded research efforts focused on the development of emission abatement strategies and has necessitated the use of subjective, low-throughput odor measurement methods.
In this study, direct measurements of malodorous VOCs
present in ambient air samples from 29 swine production facilities were used to develop a 19 component VOC odorant standard that was observed to mimic olfactory properties of swine manure. The emission profile for the standard VOC solution was optimized in a laboratory dynamic emission chamber
to simulate VOC emission profiles of swine effluent. Following the emission optimization process, the dynamic emission chamber was modified to deliver air samples containing the VOC standard to a nose cone. Analyses employing either a human panel consisting of 14 subjects or gas chromatography
were performed on the air stream from the emission chamber to assess human olfactory responses or odorant concentration, respectively. The ability of subjects to distinguish different air concentrations of the VOC standard was assessed by presenting six dilutions of the VOC standard to panelists.
Panelists were asked to compare odor intensity of each of the six air samples to a VOC reference standard of defined magnitude. Analysis of the responses using Fisher's LSD statistics showed that the subjects were sensitive to changes in air concentration of the VOC standard across dilutions
differing by 17%. The effect of chemical synergisms and antagonisms on human olfactory response magnitudes was assessed by altering the concentration of individual components in the VOC standard over a 2-fold concentration range while maintaining the other 18 components of the VOC standard
at a single air concentration. A statistically significant synergistic olfactory response was observed to occur when the air concentration of acetic acid or 3-methyl indole (skatole) was increased relative to the concentration of other VOC odorants in the standard. A statistically significant
antagonistic olfactory response was observed when the air concentration of 4- ethyl phenol was increased relative to the other VOC odorants in the standard. The collective odorant responses for swine waste VOC were utilized to develop a prediction model to estimate human odor response magnitudes
through measured air concentrations of “indicator” VOC odorants.
The results of this study show that direct multicomponent analysis of VOCs present in ambient air near animal production facilities may be applied towards estimating perceived odor intensity. Additionally, these
results show that this method may be useful to animal producers as a tool to evaluate best management practices for swine manure management systems or to air quality regulators at a method to identify production sites that represent a potential nuisance concern.
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