Evaluation of the influence of atmospheric conditions on odor dispersion from animal production sites

A 4.8 x 4.8 km (3 x 3 miles) grid of farmland in southern Minnesota was selected to observe odor dispersion from animal facilities as affected by atmospheric conditions. Nineteen trained resident-panelists living within or adjacent to the grid monitored odor events from June to November 1999. The panelists used a numerical 0 to 3 intensity scale (0 being no odor and 3 very strong odor) to assess the odor strength. A weather station was set at the center of the grid to collect weather data including temperature, relative humidity, solar radiation, wind speed, and wind direction. Odor emissions from the farms were also measured. Odors were detected more frequently in the summer than in the fall. However, very strong odors (intensity 3) were most common in the fall as a result of the removal of manure from storage basins and pits and the subsequent application of this manure onto cropland. A large majority of odor events (71%) were reported during either moderately or slightly stable atmospheric conditions (atmospheric stability classes E and F) during the evaluation period. This predictable response was further verified by the high occurrence of odor events (approximately 50%) during periods of low wind velocities (under 2.5 m/s). This result was consistent for all odor strengths (faint to very strong) identified by the reported intensities. Thus, for this particular location and animal facilities, the frequency of odor occurrences has an inverse linear relationship to the wind velocity. However, 35% of the strong odors (intensity 3) were reported under atmospheric stability class D, which indicated that neutral atmospheric condition with high wind speeds could also result in strong odors at the ground observing level.