2.4.6. Trapping Plume Shape

The first one is called as Looping, it is a super adiabatic lapse rate, which means that environmental lapse rate is greater than adiabatic. Because this one does not change adiabatic lapse rate stays where it is the other thing changes.

So, you can see that this is the environmental lapse rate and this is the adiabatic lapse rate. Now, here you can see that the wind speed is quite high... the Z variation of the plume is very high because of this particular this thing.

The Looping plume shape occurs in conditions where the environmental lapse rate (the rate at which temperature decreases with height) is greater than the adiabatic lapse rate (the rate at which a rising parcel of air cools). This situation indicates a super adiabatic lapse rate, resulting in a very unstable atmosphere. In these conditions, there is high wind speed, which creates large eddies. When the plume of pollutants is released, it tends to move erratically up and down rather than rising uniformly, resulting in a looping pattern. The Z variation of the plume is high because the instability pushes the plume to go both upward and downward frequently.

Imagine a balloon filled with hot air. When you release it, the warm air inside makes it rise, but if the surrounding air is not stable – like during a windy day – the balloon will bob up and down erratically instead of just floating straight up. This is similar to how pollutants behave under a Looping plume shape where high winds cause the plume to rise and fall unpredictably.

The next, this one is called as Coning. This is neutral, which means there are thermal forces don’t play a big part in this. The environmental lapse rate is almost the same as the adiabatic lapse rate approximately...

This is the direction of the wind, but there is also a fluctuation in the other two directions...

In the Coning plume shape, the environmental lapse rate is almost equal to the adiabatic lapse rate, indicating neutral stability. This means that thermal forces have minimal impact on the plume's movement, and it spreads primarily due to wind velocity. The plume disperses in a cone shape, widening as it moves away from the source. The turbulence in the wind causes fluctuations in the plume's behavior, leading to mixing as it rises and spreads laterally.

Think of a garden hose spraying water. If you hold the hose steady, the water flows in a straight path, but if the hose moves side to side in the wind, the spray becomes wider and more dispersed. Similarly, in Coning, the pollutant plume expands laterally as it moves in the wind.

The third condition is called Fanning, and now you see here that the adiabatic lapse rate and environmental lapse rate intersect but they intersect right below the source just below the source...

So if a pollutant is released, it is following this line. And you see that in this particular instance, the temperature of the plume is less than that of the environment.

In the Fanning plume shape, the environmental and adiabatic lapse rates intersect just below the source of the pollution. This indicates that the plume's temperature is lower than the surrounding environment, causing it to sink back toward the mixing height rather than rising. Consequently, dispersion in the vertical direction is limited, while the plume spreads outward horizontally, leading to a fan-like shape. This condition often leads to higher pollutant concentrations close to the ground.

Imagine a hot chocolate that you’ve just made. If it cools down quickly to below room temperature, it will not rise above your cup but will spread out on the surface. Similarly, the Fanning plume behaves like the cooled chocolate, spreading horizontally rather than rising.

This particular case where we have called as Fumigation, where it is exactly the opposite. There is inversion there... so whatever is released will now get contained in the zone...

There is also lofting which is similar to fanning but the mixing height is below the source...

Fumigation occurs during temperature inversion, where pollutants released from a low source become trapped and concentrated in a layer of stable air above, leading to potential high exposure levels. In contrast, Lofting occurs when the mixing height is lower than the source of the pollution, allowing the plume to disperse upwards without coming into contact with the ground. Lofting typically results in lower ground-level concentrations since the pollution is released higher up and disperses effectively.

Consider a lid on a pot of boiling water. When the lid is on, steam (pollutants) can’t escape, leading to high pressure inside (fumigation). Taking the lid off allows the steam to disperse upward into the air (lofting), reducing the concentration of steam lower down. This is reminiscent of how pollutants behave in Fumigation and Lofting scenarios.

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