At night, air may move down a slope in a narrow layer, carrying odours longer distances. The dispersion factor is calculated by adding the weighting points to the wind frequencies for 8 wind directions. If the wind comes from a direction that promotes good dispersion, the separation distance is reduced. If the wind blows down a long slope, separation distance is increased. Land use factor depends on the local zoning.
Barns can be closer to neighbours in agricultural areas.
Conclusion Predicting odour dispersion is complicated. The Austrian example was used just to illustrate some of the factors involved. Local geography, wind patterns, weather and local perceptions of odour are all variables to consider. The uncertainty involved will make odour research a very important area of study. Robert Borg, P.Eng.