Relationships between odor properties and determination of odor concentration limits in odor impact criteria for poultry and dairy barns.

Livestock odor properties have not been well understood and the role of hedonic tone (HT) in establishing appropriate odor impact criteria has not been investigated. Five odor properties, including odor concentration (OC), intensity (OI), HT, persistence, and character descriptor, were studied for odorous air from a commercial dairy barn, layer barn, and broiler barn by taking measurements in all four seasons. The seasonal OC of the dairy, layer, and broiler barns averaged 447±162OUm-3 , 583±216OUm-3 , and 766±148OUm-3 , respectively. Correspondingly, OI and HT averaged 2.7±0.5 and -2.6±0.5 for the dairy barn, 2.9±0.4 and -2.9±0.5 for the layer barn, and 3.2±0.4 and -3.1±0.4 for the broiler barn. Significant correlations were observed among OC, OI, and HT for all three odors (P<0.01). Increased OC was accompanied by increased OI but decreased HT. The relationships between OC and OI, and between OC and HT were derived in both Weber-Fechner law and Stevens' power law, while the best relationship between OI and HT turned out to be in a cubic polynomial model for the dairy-barn odor and a quadratic polynomial model for the two poultry barn odors. Based on OI-OC and HT-OC relationships in Weber-Fechner law, a reference table of OC limits was generated with 3 set values for OI (0, 1, and 2) and HT (0, -1, and -2) for all three odor sources, which may provide references in establishing appropriate odor impact criteria to meet different land use purposes. The comparison of the OC limits was made using relationships for all odor samples and for odor below 320OUm-3 (OI=3), indicating no significant difference. Slightly lower OCs from the former were suggested for use in stricter odor impact criteria.