Dispersion is poorest at night and, for a given wind speed, decreases as cloud cover decreases. The effect of weather conditions on odor dispersion. Note that the first four categories for solar radiation are functions of sun angle and cloudiness amount. The plume shapes shown in Figure 1 assume the plume is travelling over a smooth, flat surface. Rarely is the terrain surrounding a farm perfectly flat and smooth.
Landscape plays an important role in the movement of odor off-farm.
Increasing the roughness of the terrain with obstacles such as hills, trees, and buildings tends to increase dispersion in the odor plume. A filtering barrier, such as a row of trees placed downwind of the odor source increases turbulence, forcing the air to mix and lift odors upward. Land slope also changes the shape of the plume. Dispersion is increased if prevailing winds carry the plume up-slope. Down-slope or down valley winds tend to concentrate odors in lower lying areas.