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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs
ment than scentometers, are the instrumentation of the choice for the ASTM (American Society for Testing and Materials) and European Standards and are widely used for odor research. Guidelines for the design, construction, calibration, and operation of olfactometers are given in the European Standard (European Committee for Standardization, 2001). Specific requirements for panel size and selection with respect to behavior, variability, and sensitivity of panel members are also provided. The minimum panel size in any measurement is four, but larger numbers are recommended to improve repeatability and accuracy. The scentometer may be more appropriate for ambient measurements (property line, downwind of source, etc.) than the olfactometer.
Instruments available to identify and measure the concentrations of specific odorants include gas chromatography coupled with mass spectrometry (GC-MS) for component identification. Some of these methods are sensitive in detecting compounds at very low concentrations. Peters and Blackwood (1977) reported difficulty in positively identifying compounds present in feedlot air samples using GC-FID. (Low peak values precluded the use of GC-MS for amines.) As a result of the low concentrations of many AFO odorants, their components may have to be concentrated prior to analysis using methods such as solvent desorption, thermal adsorption (Zahn et al., 1997), or solid-phase microextraction (SPME) (Zhang et al., 1994). It must be emphasized that chemical techniques should be buttressed by sensory methods to correlate instrumental results with human odor perception.
The relatively high cost per sample of odor panels has created the need for reproducible, inexpensive instruments (electronic noses) capable of making measurements that correlate with the human olfactory response (Lacey, 1998). Lacey (1998) and Mackay-Sim (1992) listed several electronic approaches to volatile gas (odor) detection, including metal oxide semiconductors, field-effect transistors, optical fibers, semiconducting polymers, and piezoelectric quartz crystal devices. These approaches raise the possibility of remote odor monitoring or surveillance networks for individual compounds or odorant mixtures. Piezoelectric crystals are sensitive to changes in surface mass caused by adsorption of gas molecules. As mass is added to the surface, the resonant frequency decreases and can be measured precisely. The crystal surface can be made to respond to single chemicals or groups of chemicals. Some sensors may be affected by water vapor, methane, and temperature (Lacey, 1998).
Electronic methods should be tested against olfactometry results to be validated against human sensory responses.
FINDING 5. Standardized methodology for odor measurement have not been adopted in the United States.
Standardized methodology should be developed in the United States