Odour is diluted by dispersion as it is transported in the atmosphere. The further it travels, the
more it is diluted. Therefore, adequate setback distances are a key in preventing odour
complaints. The important factors that influence odour dispersion are wind, atmospheric stability,
and topography. Odour is carried by wind from the source to the receptor. Therefore, the
prevailing wind direction should be considered when choosing sites for livestock facilities. The
wind direction should be checked before agitating and spreading manure to avoid odour being
carried to neighboring residences by the wind. The atmospheric stability is commonly described by the Pasquill stability classes: A – strongly
unstable; B – moderately unstable, C – slightly unstable; E – slightly stable, F – moderately stable,
and D – neutral (overcast). Odour is diluted quickly when the atmosphere is unstable. Therefore, it
is a good practice to spread manure when the atmosphere is unstable so that odour is diluted to an
acceptable level before it reaches the receptor (residences).

If possible, livestock facilities should be built on relatively flat topography for good dispersion. It
should be avoided to build facilities near hills to prevent the effect of aerodynamic downwash.
Windbreaks (walls, trees and shrubs) may be used to trap odour and dust, and to create more air
turbulences for stronger dispersion. The dispersion theories (eg., Gaussian dispersion model) indicate that increasing the odour
release height reduces odour intensity at the ground level. Exhaust stacks (chimneys) may be used
to raise the release points of the ventilation air, thus to reduce odour complaints originated from
animal buildings.