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From a point source, a plume of odor is created. It moves with the wind, dependent on wind velocity, direction and air density (which is dependent on humidity and elevation). As the plume is released it travels from the source and is diluted by diffusion of the odorous chemicals which is caused by interaction between the air molecules and those of the chemical. This is a small effect and can be envisioned as marbles, widely separated, but occasionally bouncing against one another. The odor chemicals change direction very little so that they remain within the plume.
Stratification of the plume in an air mass occurs when there is a dense layer of air over which lighter weight air moves. In the event of high humidity at ground level, that air is of lower density than the mass of air above and the result is that the plume containing air can settle. Inversions occur frequently and the exact level at which a plume of odor will be found is difficult if not impossible to predict. Thus a plume of odor "skips" over some areas and seems to be more noticeable in others.
A strong wind carries the odorous chemicals in a concentrated band, whereas a variable wind will spread the plume over a wider area.
The dominant cause of diffusion is turbulence which is caused by an interaction between the plume as it travels downwind and structures in its path.
To affect the plume one can release the odor at a higher elevation (this is the approach used in the phosphate and electric generating industries, as examples, to dissipate released material.) It is costly as it requires tall stacks to place the plume far above the surface, permitting it to be spread over a wide area.
Where topography of the land is variable (as example in a mountainous area) interaction between the plume and vegetation is encouraged.) The problem in low-lying flat terrain is that there is no interruption of the plume's directional or velocity components, so that the odorous chemicals continue in a concentrated form.
Mechanically a plume can be dissipated at the source by interjecting air into the stream (this approach is used in air handling systems to increase diffusion of heat from a point source, as example: air conditioning systems.)
Destroying the chemicals within the plume is the best solution to the problem and has long be the accepted way to control obnoxious (or noxious) release (a flame is seen at refineries, older wastewater treatment plants, and other facilities where pollution of the environment is unwanted.) The odorous chemicals are burned in the process.
Passing the offending gas through an adsorbent materials is often used. One of the most widely used adsorbents is water. It is highly effective in trapping the odorous compounds, but of course the water becomes contaminated in the process and needs to be recycled.
The least practical solution to correcting an odor problem is use of masking agents. While this may be partially effective in controlling household odors, it only adds to the problem and in some cases, individuals may find the new odor more obnoxious than the old. Not unlike riding in a elevator with someone who has used a heavy dose of aromatics to either mask smells, or attract attention. Beauty (and an attractive aroma) is in the eye (and nose) of the beholder.
Waste water treatment plants are becoming the most obvious and noxious source of plumes containing organic, nitrogen and sulfur chemicals that are released into the air. The effect on animals (including man) and vegetation of these point source air pollutants is unknown. Florida seems to have more than its share of waste water treatment plants that are oblivious to the problem. Longboat Key and other barrier islands off Sarasota's waterfront are exposed to the smells, complements of Sarasota. Both North and South of Tampa on I-75 new facilities serving the expanding communities likewise are polluting the air. These "aromatic" plumes are quite democratic as, dependent upon the direction of the wind, other areas are entitled to share.
Call the fragrance what you like; fetid, fecal, waste or sewage handling in tomorrow-land stench, something needs to be done.
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