Evaluation of OFFSET (Odor Setback Model) Using Neighborhood Monitors

A comparison between observed and predicted odor intensities at neighbor's living in the vicinity of various livestock farms in 5 different Minnesota counties was made to evaluate an odor setback tool developed by the University of Minnesota. In 309 out of 570 reported odor events the farms participating in the investigation were the probable odor sources. In 199 (64%) of these an odor less than intensity 2 was predicted but an odor intensity equal to 2 or above was reported. In 99 cases (32%) the predicted and reported odor intensity was in agreement, being either higher than 2 or below 2. Regarding all observations the observed odor intensity was significantly higher than the predicted. Possible reasons for these mixed results are; variations in odor rating and sensitivity of resident recorders, wind speed fluctuations, possible errors and fluctuations in odor emissions from each farm (only one emission measurements were made at each farm), topographic variation between sites since OFFSET assumes flat surfaces, and background emissions from other sources that may have contributed to what resident recorders were smelling.