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A plume is a column of liquid, gas, or dust, moving through another fluid. In the context of air pollution, a plume refers to a column of pollutants in the atmosphere, which can be visible or invisible. These pollutants can be in the form of gases, particles, or a combination of both, and they are released into the atmosphere through various sources, such as industrial processes, volcanic eruptions, wildfires, and everyday activities like vehicle exhaust. The behaviour of a plume, including its movement and dispersion, is influenced by factors such as wind speed, direction, and atmospheric stability. Atmospheric stability refers to the resistance of the atmosphere to mixing, which is influenced by heating and cooling at the ground. Buoyancy, momentum, and diffusion also play a role in determining the motion of the plume. Understanding plume behaviour is crucial for assessing the impact of natural and human-made pollution on the surrounding environment.
| Characteristics | Values |
|---|---|
| Definition | A plume is a column of air pollutants released into the atmosphere |
| Composition | Gases, smoke, particles, or a combination of both |
| Sources | Industrial processes, volcanic eruptions, wildfires, vehicle exhaust, everyday human activities, and natural occurrences |
| Behaviour | Depends on the source characteristics, atmospheric conditions, and properties of the emitted substance |
| Types | Fanning plume, Lofting plume, Fumigating plume, Trapping plume, Neutral plume, Buoyant plumes, Passive or neutral plumes |
| Dispersion | Influenced by factors such as wind, buoyancy, turbulence, and atmospheric stability |
| Modelling | Dense gas models, Box model, Gaussian model, Lagrangian model, Computational Fluid Dynamics (CFD) |
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What You'll Learn
- Plumes are formed by human activities and natural occurrences
- Plumes can be columns of liquid, gas, or dust
- Plume behaviour refers to the movement and dispersion of plumes
- Plume shapes are influenced by flow in the ambient fluid
- Atmospheric stability describes how much upward and downward mixing of a plume occurs
Plumes are formed by human activities and natural occurrences
Plumes are columns of liquid, gas, or dust, moving through another medium. They are formed by human activities and natural occurrences. Human sources of air pollution include the burning of fossil fuels, such as industrial processes, factory exhaust, and vehicle exhaust. Household and agricultural pollution also contribute to air pollution. For example, smoke from a chimney or steam from a smokestack at a power plant is considered a plume.
Natural sources of air pollution include dust generated by wind, wildfires, and volcanic activities. Wildfires, for instance, generate smoke and other pollutants that rise upward due to buoyancy generated by the hot fire. Similarly, volcanic eruptions release heated gases and particles that form lofting plumes. These plumes exhibit significant buoyancy effects and rise rapidly in the atmosphere.
Lofting plumes are characterized by a strong upward displacement due to the temperature difference between the emitted substance and the surrounding air. They are commonly associated with sources that emit heated gases or particles. For instance, industrial processes that involve high-temperature emissions can create lofting plumes. The buoyancy of the plume, determined by the temperature difference, influences how high and wide it rises and spreads in the atmosphere.
In contrast, trapping plumes occur when the emitted substance is confined to a specific area due to local atmospheric conditions or topographic features. Stable atmospheric conditions, such as inversions, can act as a "capping lid", preventing the upward mixing of plumes and trapping pollution near the ground. This can lead to hazardous levels of pollutant concentrations at ground level.
Human activities, such as burning fossil fuels, and natural occurrences, such as wildfires, contribute to the formation of plumes and air pollution. These plumes can have significant impacts on the environment and human health, depending on their composition and dispersion. Understanding plume behaviour is crucial for managing air quality and mitigating the harmful effects of pollution.
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Plumes can be columns of liquid, gas, or dust
A plume is a column of liquid, gas, or dust, moving through another medium. Plumes can be generated from various sources, including industrial processes, volcanic eruptions, wildfires, and everyday activities like vehicle exhaust. They can also be natural or human-made. For example, in the Bay Area, most air pollution comes from man-made sources, such as car exhaust pipes and smokestacks from factories.
The movement and dispersion of plumes are known as plume behaviour. Plumes can exhibit different behaviours, such as fanning, fumigating, looping, coning, trapping, neutral, and lofting. A fumigating plume, for instance, is a behaviour where the plume spreads close to the ground, resulting in the widespread dispersal of the emitted substance. This type of behaviour is often observed in pesticide or insecticide spraying activities.
The shape and behaviour of a plume are influenced by various factors, including the flow of the ambient fluid, momentum, diffusion, buoyancy, and temperature differences. As a plume moves away from its source, it typically widens due to entrainment of the surrounding fluid at its edges. This widening is known as dispersion and occurs when the edges of the plume mix with the surrounding air. The rate of entrainment into the plume is proportional to the local velocity.
Buoyancy plays a crucial role in determining how much a plume rises and spreads in the atmosphere. It is influenced by density differences between the plume and the surrounding fluid. When the plume is less dense than its surroundings, it exhibits positive buoyancy and tends to rise. On the other hand, when the plume is denser, it may still exhibit negative buoyancy and rise vertically if it has sufficient initial momentum.
Plumes can also be classified as pure jets or pure plumes, depending on whether they are driven primarily by momentum or buoyancy effects, respectively. In some cases, plumes may transition from being momentum-dominated to buoyancy-dominated as they move away from their source. This transition can be predicted using the Richardson number, a dimensionless number that characterises the flow.
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Plume behaviour refers to the movement and dispersion of plumes
The behaviour of a plume is influenced by various factors, including wind conditions, atmospheric stability, and the vertical temperature profile. For instance, when the wind blows across the path of a plume, it causes a fanning plume, where the plume spreads out horizontally, resembling a fan shape. This is often observed in open areas or near bodies of water. Conversely, a fumigating plume occurs when the plume descends and spreads close to the ground, resulting in the widespread dispersal of the emitted substance. Fumigating plumes are commonly seen in pesticide or insecticide spraying activities.
Another type of plume behaviour is the coning plume, which occurs when the emitted substance has a higher velocity at the source, causing the plume to narrow and converge as it rises, resembling a cone shape. Coning plumes are often observed in chimney emissions or jet engine exhaust. A trapping plume occurs when the emitted substance is trapped within a specific area due to local atmospheric conditions or topographic features, such as stable layers of air above the plume or valleys with strong temperature inversions.
Lofting plumes are characterized by significant buoyancy effects, rising rapidly in the atmosphere due to the temperature difference between the emitted substance and the surrounding air. They are typically associated with sources that release heated gases or particles, such as wildfires and industrial processes involving high-temperature emissions. The shape and behaviour of plumes can also be influenced by the flow of the ambient fluid, with local wind blowing in the same direction as the plume, transitioning from 'buoyancy-dominated' to 'momentum-dominated'.
The study of plume behaviour is crucial for understanding the dispersal patterns of gaseous pollutants in the atmosphere and their impact on air quality. Atmospheric stability, the resistance of the atmosphere to mixing, is influenced by heating and cooling at the ground, with warmer air rising and creating unstable conditions, while cooler air near the ground during the night creates stable conditions that can trap pollution.
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Plume shapes are influenced by flow in the ambient fluid
A plume is a column of liquid, gas, or dust, moving through another. In the context of air pollution, a plume refers to a column of pollutants in the atmosphere. These can be visible or invisible columns of gas, smoke, or other substances emitted into the atmosphere. Plumes can be generated from various sources, including industrial processes, volcanic eruptions, wildfires, and everyday activities like vehicle exhaust.
Plume behaviour refers to the movement and dispersion of these plumes. Several effects control the motion of the fluid, including momentum (inertia), diffusion, and buoyancy (density differences). The shape of a plume can be influenced by the flow in the ambient fluid. For example, if the local wind blows in the same direction as the plume, it results in a co-flowing jet. This causes a transition from a "buoyancy-dominated" plume to a "momentum-dominated" plume. This transition is usually predicted by a dimensionless number called the Richardson number.
The rate of entrainment into the plume is proportional to the local velocity. Entrainment refers to the process where the plume widens due to the entrainment of the surrounding fluid at its edges. The entrainment coefficient, which is the key parameter in simple plume models, varies with the local Richardson number. Typical values for the entrainment coefficient are about 0.08 for vertical jets and 0.12 for vertical, buoyant plumes.
The phenomenon of laminar flow versus turbulent flow is also important in plume behaviour. As a plume moves away from its source, it typically transitions from laminar to turbulent flow. This can be observed in the rising column of smoke from a cigarette. Computational fluid dynamics (CFD) can be used to simulate plumes when high accuracy is required, but the results are sensitive to the chosen turbulence model.
The initial shape of the plume also plays a role in its behaviour. The impact of the plume depends on the initial shape of the source distribution and the intensity of the horizontal background flux. The rate of mixing is influenced by the viscosity and density of the ambient fluid, and the length of the plume's interface. The source orientation becomes a significant factor when the background flow velocity is higher, affecting the degree of mixing and the plume shape.
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Atmospheric stability describes how much upward and downward mixing of a plume occurs
A plume is a column of liquid, gas, or dust, moving through another. In the context of air pollution, a plume refers to a column of pollutants in the atmosphere. These can be visible or invisible columns of gas, smoke, or other substances emitted into the atmosphere. Plumes can be generated from various sources, including industrial processes, volcanic eruptions, wildfires, and everyday activities like vehicle exhaust.
The behaviour of a plume refers to the movement and dispersion of these columns of pollutants. The dispersion of a plume occurs when its edges mix with the surrounding air. This upward and downward mixing is influenced by atmospheric stability, which describes the resistance of the atmosphere to mixing. Atmospheric stability is influenced by heating and cooling at the ground. During the daytime, the land surface is heated by the sun, warming the air near the ground. This warmer air is less dense and rises, creating an unstable condition that promotes mixing in the atmosphere.
On the other hand, at night, the ground surface cools, causing the air near the ground to become denser and heavier. This stable condition prevents the air from mixing, often trapping pollution near the ground. This stable condition is further influenced by inversion layers, which act as a "capping lid", preventing the upward mixing of plumes and potentially leading to hazardous pollutant concentrations at ground level.
The buoyancy of a plume, influenced by temperature differences, also plays a role in its upward and downward mixing. Lofting plumes, for example, exhibit significant buoyancy effects and rise rapidly due to the temperature difference between the emitted substance and the surrounding air. Conversely, a neutral plume remains relatively stable with minimal buoyancy effects, rising vertically without significant upward or downward displacement.
The shape and behaviour of plumes can also be influenced by factors such as wind speed and direction, resulting in phenomena like fumigating, looping, or coning plumes. Overall, atmospheric stability is a critical factor in determining the extent of upward and downward mixing of a plume, influencing the dispersion and impact of air pollutants.
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Frequently asked questions
A plume is a column of liquid, gas, or dust, moving through another. In the context of air pollution, a plume is a vertical body of fluid moving through the air.
There are several types of plumes, including:
- Trapping Plume
- Neutral Plume
- Lofting Plume
- Fumigating Plume
- Looping Plume
- Coning Plume
The shape of a plume is influenced by the flow of the ambient fluid, such as wind blowing in the same direction as the plume. This can cause a transition from a "buoyancy-dominated" plume to a "momentum-dominated" plume.
Plumes disperse when they mix with the surrounding air, causing the pollutant to spread out and become less concentrated. This dispersion is influenced by factors such as wind speed and direction, as well as topography.
Plume behaviour refers to the movement and dispersion of plumes. It includes various types such as fanning, fumigating, looping, coning, trapping, neutral, and lofting. Plume behaviour is influenced by factors like wind speed, direction, and atmospheric stability.
