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Plume types are important because they help us understand under what conditions there will be higher concentrations of contaminants at ground level.
The different plumes are created by changes in atmospheric conditions. For example, when temperature decreases upward faster than 1°C / 100 m, conditions are unstable, creating a looping plume. Neutral conditions occur when temperature decreases at 1°C / 100 m, and stable conditions occur when temperature increases with height, resulting in a fanning plume.
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Looping Plume: dissipates in patches and relatively rapidly with distance. High probability of high concentrations sporadically at ground level close to stack. Occurs in unstable atmospheric conditions. |
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Coning Plume: standard plume, large probability of ground contact some distance downwind. Occurs in neutral atmospheric conditions. |
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Fanning Plume:
Usually occurs at night, or 1200m-1800m above ground. There is high ground concentration if stack is short or if plume moves through rugged terrain. Occurs in stable inversion atmospheric conditions. |
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Lofting Plume: favourable in the sense that fewer impacts at ground level. Pollutants go up into environment. They are created when atmospheric conditions are unstable above the plume and stable below. |
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Fumigation:
most dangerous plume: contaminants are all coming down to ground level. They are created when atmospheric conditions are stable above the plume and unstable below. This happens most often after the daylight sun has warmed the atmosphere, which turns a night time fanning plume into fumigation for about a half an hour. |
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