Application: used for odors from buildings and manure storage


  • Very effective when done prior to construction.
  • Modeling can assist with decisions.
  • Information can assist with communication with neighbors.


  • Not helpful on existing facilities.
  • Most models do not account for terrain impacts.
  • Does not reduce emission, only odor impact.
Figure 1. Wind rose for Des Moines, Iowa, July.
(Courtesy of National Pork Board)
Wind rose for Des Moines, Iowa, July.


It may sound like an over-simplification, but properly siting an animal facility and associated manure storage is likely the most important odor control technology that can be implemented. This, however, must be done before the facility is constructed and it only truly addresses odor and no other emitants.

Care in siting a new facility in relation to neighbors, highways, parks and municipalities is important when avoiding the potential for odors. Separation distance, predominate wind direction, exposure angle, and terrain are all important considerations.

Wind Direction: Predominate wind direction varies by location and season and is often different than people might perceive to be the predominate direction. For instance, in Iowa many people assume the predominate summer wind direction is SW, but weather data indicates S and SSE occur more frequent. It is important to find data to support wind direction assumptions in your region. Wind data is normally available as a “wind rose”. The example in Figure 1 is for July in Des Moines, IA. This indicates that approximately 13% of the time the wind is from the south and approximately 11% of the time the wind is from the SSE. This would indicate that locating a facility on a site with neighbors to the north would be a bigger concern than would residences to the east, west or north. This wind rose is only for July and other months will vary in their percentage and directions. Winter wind directions, especially those from November through February, are less of a concern because of the limited time people tend to spend outdoors.

Figure 2. Effect of site layout and distance on exposure angle.
(Courtesy of National Pork Board)
Effect of site layout and distance on exposure angle.

Exposure Angle: When siting a building it is important to minimize the hours of downwind exposure to a swine facility. The exposure angle defines what specific wind directions will result in a receptor being directly downwind from the facility and can be combined with the wind rose to give potential hours of exposure. Figure 2 illustrates the impact of site configuration on exposure angle. The smaller the angle, the fewer wind directions will impact the neighbor. In Figure 2, for instance, the top configuration will expose neighbors to odor potential when the wind is from a specific 11 degree angle but the second configuration, where buildings are end to end, would result in a much larger angle which would increase the odor transmission potential.  Added distance always reduces this angle as well, as can be seen in the last illustration of Figure 2.

Terrain: Odor transmission potential can be impacted by terrain such as trees, hills and valleys. Trees will generally help to cause a disruption of the odor plume leaving a production site and can be implemented as a vegetative environmental buffer. Hills and valleys will sometimes channel the air flow so that it may not follow the natural wind direction, especially during evenings or other period when wind speed is low. The phenomena, sometimes referred to as “air drainage” is not easily modeled but should be considered when evaluating a potential building site.

Distance: Separation distance is always an important consideration because it provides an opportunity for potential odors to dissipate before reaching a neighbor. However, due to wind direction, exposure angle and terrain, distance is not equally important in all directions.

Models: There are several models available that have been developed to provide some unbiased siting feedback to persons evaluating sites for new construction. These generally are used to predict distances required to keep the hours of potential odor nuisance to a specified level. One of the first models developed specifically for livestock was the University of Minnesota’s Odor From Feedlot – Setback Estimation Tool (OFFSET). This model uses known emission rates from multiple sources on a farm to predict the total odor emission factor. This factor is used in conjunction with a data that relates to a desired level of “annoyance-free” hours to predict a required separation distance to meet these conditions. The model was developed in Minnesota but has been used with caution in other locations even though weather patterns may differ.

South Dakota State University and the University of Nebraska developed a model based on OFFSET called the Odor Footprint Tool (OFT). This model uses regional weather data and provides setback distances for four directions, each covering one quadrant of compass directions. This allows better fine tuning based on wind patterns and means that separation distance in some directions may be smaller than other directions because of the frequency of wind from a given directions.

The Community Assessment Model (CAM) developed by Iowa State University is receptor-based rather than being source based. Most other models examine the potential odor plume from one farm. The CAM model requires all the coordinates of neighbors (receptors) to be entered into the model along with existing odor sources along with the proposed new site. The model then tabulates the number of hours of potential odor exposure for each residence from all existing sources and the number of hours the new source would add. The premise is that multiple sources in a community may impact a receptor. The receptor likely does not differentiate which source is causing an odor event, only that there is an odor event. This model, therefore, focuses more on the total odor impacting a given neighbor and not just the odor from one source. 



Component Reduction Notes
NH3 0%  
H2S 0%  
Odor 100% impact on neighbor
Particulate Matter 0%  
Volatile Organic Compounds (VOC) 0%  
Cost $ modeling and new site

Cost Considerations

Using the principles of good siting is good practice and may have no associated cost. There may be occasions when a site is found to be unsuitable and additional cost is required to purchase a more suitable site. Proper siting may help with neighbor relations and may avoid potential nuisance law suits as well. Modeling can be free in some states and there may be a cost in others. Minnesota, Nebraska and South Dakota models are generally free. Iowa’s CAM model is run in conjunction with the Coalition to Support Iowa’s Farmers and is normally done at no cost.


Hoff, S.J., D.S. Bundy, J.D. Harmon. 2008. Modeling receptor odor exposure from swine production sources using CAM. Applied Eng in Ag 24(6):821-837.

Hoff, S.J., D.S. Bundy, J. Harmon, C.D.Johnson.  2008.  A receptor-based siting strategy for swine production systems. In: Mitigating Air Emissions from Animal Feeding Operations.  Conference Proceedings, May 19-21, 2008 (Des Moines, IA). Iowa State University. pp. 15-20.

Jacobson, L.D., H. Guo, D.R. Schmidt, R.E. Nicolai, J. Zhu, K.A. Janni. 2005. Development of the OFFSET model for determination of odor-annoyance-free setback distances from animal production sites: Part 1. Review and Experiment. Trans of the ASAE 48(6):2259-2268.

Stowell, R., C. Henry, C. Powers, D. Schulte. 2008. Siting animal production facilities and evaluating odor control options using the odor footprint tool. In: Mitigating Air Emissions from Animal Feeding Operations. Conference Proceedings, May 19-21, 2008 (Des Moines, IA). Iowa State University. pp. 2-6.

Livestock and Poultry Environmental Learning Community:

Research Summary: Siting Swine Facilities Using Iowa State’s Community Assessment Model
Planning Livestock & Poultry Facilities for Reduced Odor Risk

Iowa State University:

Iowa Wind Roses

University of Nebraska:

Odor Footprint Tool

National Pork Board: 

Siting and Building Design Considerations to Reduce Odor Potential from Swine Facilities.