Correlation of odor dilution threshold and H₂S and NH ₃ concentrations for animal feedlots

Odor quantification using an olfactometer and panelists is very expensive. Among the numerous components of odors from animal sources, hydrogen sulfide and ammonia are two important and easily measured gases that could possibly be used as odor indicators. A total of 1152 air samples were taken from 260 sources on 80 livestock/poultry farms in Minnesota and measured for odor dilution threshold, H₂S, and NH₃ concentrations. The data were analyzed to determine whether or not H₂S and NH₃ concentrations correlated with odor dilution threshold. It was found that H ₂S was linearly correlated with odor threshold to various degrees. For all animal species, the coefficient of determination (r²) was 0.569. For various swine facilities, the coefficient of determination (r ²) ranged from 0.433 to 0.934. Swine manure storage units had better linear correlation than building sources (r²: 0.701 vs. 0.443). Cattle operations had a weak linear relationship (r²=0.384 to 0.617). Cattle manure storage units had a better linear correlation than building sources (r²: 0.617 vs. 0.384). For all air samples from poultry buildings and composting sites, H₂S and odor threshold correlated linearly (r²=0.781). However, this correlation was weaker for poultry buildings (r²=0.279) and composting sites (r²=0.512). These results, indicate that H₂S can be used as an odor indicator for some animal facilities. No correlation was found between NH₃ and odor threshold except swine wean-to-finishing barns (r²=0.677).