Wind and weather are the major factors influencing how well gases are dispersed. Temperature inversions, typically caused by calm, clear nights with rapid surface cooling create problems. With inversions, air temperature increases with height above ground level. A plume from a chimney will not disperse or will be forced down to ground level and carry odours longer distances. Gas dispersion from tall chimneys, Gaussian dispersion models.
Manure gases all behave differently and interact in unpredictable ways.
Almost 200 chemicals have been identified, many with very low perception threshold levels. People's reaction to odours also varies a great deal. Persistence - a calculated relationshop between intensity and dilution. Odours entrained in building wake, poor dispersion. A siting model being proposed for Austria can be used to illustrate the factors to be considered in predicting odour protection separation distances.