Air pollution meteorology deals with the meteorological processes near to the earth’s surface which consist of the impacts of meteorology on air pollutants and the effects of pollutants on meteorology. Air pollution meteorology studies how meteorological conditions affect the dispersion and behavior of pollutants. This field is crucial for understanding how various plume types—such as buoyant, neutral, and dense—interact with atmospheric conditions. By analyzing air pollution meteorology, we can better grasp how factors like wind patterns, temperature inversions, and humidity influence plume behavior and air quality. Understanding these interactions helps predict pollution dispersion and mitigate its impact on health and the environment. With insights into types of plumes and their behavior, we can develop more effective strategies for managing and reducing air pollution.
In this blog, I will show you some important terms related to air pollution meteorology, environmental stability and types of plumes.
If the air is still and pollutants are unable to disperse, the local concentration of pollutants will rise. Strong, turbulent winds, on the other hand, remove pollutants fast, resulting in reduced pollutant concentrations.
Thus, the destiny of air pollutants is influenced by air movements. As a result, any study of air pollution should also include a look at the weather patterns in the area that is meteorology.
The following are some of the benefits of analysing meteorological data:
- Identify the source of pollution.
- Predict the occurrence of inversions and days with high pollutant concentrations.
- Simulate and predict air quality with the help of computer models.
Also read : Air Pollution Causes – A Comprehensive Guide
Meteorological Factors affecting Air Pollution
Meteorological factors significantly influence air pollution meteorology by affecting plume behavior and dispersion. Wind speed and direction determine how different types of plumes—such as buoyant or dense—spread. Temperature inversions can trap pollutants, altering plume types and intensifying air pollution. Humidity and atmospheric pressure also impact the dispersion and behavior of pollutants, influencing overall air quality.
The following factors should be measured while examining air quality. They can help us better understand the chemical reactions that take place in the atmosphere.
- Wind speed and direction
- Temperature
- Humidity
- Rainfall
- Solar Radiation
Wind Speed and Direction
In air pollution meteorology, wind speed and direction are crucial for plume behavior. High wind speeds can disperse pollutants widely, affecting various types of plumes, while calm conditions may lead to plume stagnation and localized air pollution. Understanding these factors helps predict air quality changes.
Temperature
Temperature influences air pollution meteorology by affecting plume behavior. Higher temperatures can enhance plume rise, dispersing pollutants more effectively. Conversely, temperature inversions trap pollutants near the ground, altering plume types and intensifying air pollution. Temperature variations thus play a key role in determining pollutant dispersion patterns.
Humidity
Humidity impacts air pollution meteorology by affecting the size and behavior of pollutant plumes. High humidity can lead to the formation of secondary pollutants and alter plume types, while low humidity may enhance pollutant dispersion. Understanding humidity’s role is essential for accurate air quality assessments.
Rainfall
Rainfall affects air pollution meteorology by removing pollutants from the atmosphere through washout processes. It can change plume behavior, reducing pollutant concentrations in the air. The type and intensity of rainfall influence how different types of plumes are affected, impacting overall air quality and pollution levels.
Solar Radiation
Solar radiation influences air pollution meteorology by driving chemical reactions in the atmosphere. It affects plume behavior by promoting the formation of secondary pollutants and influencing thermal patterns that impact plume types. Solar radiation’s role is crucial in understanding how different types of plumes disperse and interact with the environment.
Lapse Rate in Air Pollution Meteorology
- The rate of change in the measured temperature as we move up through the Earth’s atmosphere is known as the lapse rate.
- When the temperature drops with elevation, the lapse rate is positive.
- It is zero when the temperature remains constant with elevation.
- When the temperature rises with elevation the adiabatic lapse rate is negative. This is called temperature inversion.
In air pollution meteorology, the lapse rate—the rate at which air temperature decreases with altitude—significantly impacts plume behavior. A normal lapse rate facilitates the rise and dispersion of plumes, aiding in the dilution and spread of pollutants. Conversely, a temperature inversion, where the lapse rate is negative, traps plumes near the ground, leading to higher pollutant concentrations and altered plume types. Understanding the lapse rate is essential for predicting how different types of plumes will behave in various atmospheric conditions, affecting overall air quality and pollution levels. Accurate knowledge of lapse rates helps in effective air pollution management and forecasting.
Environmental Lapse Rate
The rate of decrease of temperature with altitude in the stationary atmosphere at a given time and location is known as the environmental lapse rate (ELR). The International Civil Aviation Organization (ICAO) has defined an international standard atmosphere (ISA) with a temperature lapse rate of 6.49 K/km (1.98 °C/1,000 ft) from sea level to 11 km.
(dT/dz)env = -6.5 K / 1000 metres
The environmental lapse rate in air pollution meteorology affects plume behavior by influencing how different types of plumes rise or stay grounded, impacting the dispersion and concentration of pollutants.
Adiabatic Lapse Rate
The adiabatic lapse rate (ALR) refers to the rate with which the temperature of an air parcel changes in response to compression or expansion associated with elevation change. This process is assumed to be adiabatic, that is, no heat exchange happens in between given air parcel and its surrounding.
(dT/dz)adia = -g/Cp = -9.86 0C / 1000 metres
Where,
g = acceleration due to gravity
Cp = Specific heat at constant pressure
The adiabatic lapse rate in air pollution meteorology defines how temperature changes with altitude for rising or descending plumes. This influences plume types and their dispersion characteristics and behavior.
Atmospheric Stability
The degree of atmospheric stability plays a key role in the ability of atmosphere to disperse the pollutants emitted to it. It is determined by comparing ELR and ALR.
When ELR = ALR, the atmosphere is neutrally stable.
If ELR > ALR, the atmosphere is superadiabatic and unstable.
When ELR < ALR, the atmosphere is subadiabatic and stable.
Under an unstable atmospheric condition, the lapse rate is super adiabatic. The actual temperature gradient is more negative than the dry adiabatic temperature gradient. A rising parcel of air gets warmer and tends to travel upwards due to increasing buoyancy. Air from different altitudes mixes thoroughly. There is rapid dispersion of pollutants throughout the entire atmosphere. As a result, this is highly desirable in pollution prevention.
Under a stable atmospheric condition, the lapse rate is subadiabatic. In this condition, a rising parcel of air gets denser, cooler and tends to fall back. The vertical mixing is very less and the dispersion of pollutants is very slow.
Atmospheric stability in air pollution meteorology determines how air layers resist or promote vertical movement, affecting plume types and behavior, and influencing the dispersion and mixing of pollutants.
Types of Plume
A plume is a column of liquid, gas, or dust that moves through another fluid, gas, or dust. The term plume is commonly used to describe things like smoke rising from a chimney. Depending on the degree of atmospherical instability, exit velocity from a stack and the prevailing wind turbulence, the plume emitted from a stack behave in different ways.
In air pollution meteorology, plume types refer to the behavior of pollutant emissions as they disperse in the atmosphere. Each plume type exhibits distinct behavior based on meteorological conditions, influencing how pollutants spread and affect air quality. Common types of plumes include
- Coning Plume
- Fanning Plume
- Looping Plume
- Lofting Plume
- Fumigating Plume
- Trapping Plume
Coning Plume
In air pollution meteorology, a coning plume occurs when pollutant emissions disperse in a vertical cone shape. This plume type typically forms under neutral atmospheric conditions, where temperature and wind speed are relatively consistent with height. The coning plume’s symmetrical spread limits its horizontal dispersion, keeping pollutants concentrated near the emission source. Understanding this plume behaviour is crucial for predicting pollutant distribution in various meteorological scenarios, influencing air quality management strategies.
- Formed when horizontal wind velocity exceeds 32 km/h and cloud blocks solar radiation during the day and terrestrial radiation during the night.
- There is little vertical mixing.
- The environment is slightly stable under sub-adiabatic conditions (ELR<ALR).
- The plume shape is vertically symmetrical about the plume line.
Fanning Plume
In air pollution meteorology, a fanning plume occurs under stable atmospheric conditions, where the environmental lapse rate is less than the adiabatic lapse rate.
- Fannin plume types are formed at extreme inversion conditions owing to a negative lapse rate.
- When the environment is under conditions of inversion, a stable environment occurs just above the stack, and the plume moves horizontally rather than upwards.
- Occurs more frequently when there is less turbulence.
- For high stack, fanning is considered a favourable meteorological condition as it doesn’t cause ground pollution.
Looping Plume
In air pollution meteorology, a looping plume forms under highly unstable conditions, causing the plume to rise and fall, leading to erratic pollutant dispersion.
- The wavy looping plume arises in a super adiabatic environment (ELR>ALR), resulting in a very unstable atmosphere due to rapid mixing.
- In an unstable atmosphere, rapid vertical air motions occur both upward and downward, resulting in a looping plume.
- As a result, large pollution concentrations may arise near the ground.
- It is preferable to create high stacks where the environment is normally hyper adiabatic to scatter these contaminants.
Neutral Plume
In air pollution meteorology, a neutral plume occurs in neutral atmospheric conditions, where plume behaviour is neither buoyant nor sinking, maintaining a steady dispersion.
- In neutral atmospheric circumstances (ELR=ALR), a neutral plume forms.
- A neutral plume rises vertically in an upward direction.
- The plume will continue to rise until it reaches a height where the density and temperature of the surrounding air are equal.
Lofting Plume
In air pollution meteorology, a lofting plume rises above a stable layer of air, enhancing dispersion. This plume type benefits from favorable plume behavior for pollutant spread.
- Lofting plume is produced by a strong super adiabatic lapse rate immediately above the stack and a negative lapse rate (inversion) immediately below the stack opening.
- The downward movement is stopped by inversion.
- This results in a very rapid and turbulent upward mixing of the plume. But the downward mixing is less.
- As a result, the dispersion of pollutants becomes quick, and pollutants cannot come down to the ground.
- Such a plume is good for dispersing air contaminants and providing significant protection to living beings.
Fumigating Plume
In air pollution meteorology, a fumigating plume descends from an inversion layer, causing pollutants to concentrate near the ground, illustrating adverse plume behavior.
- The fumigant plume is the exact opposite of the lofting plume.
- Formed when there is a negative lapse rate (inversion) just above the stack and a strong super adiabatic lapse rate below the stack.
- Pollutants cannot escape above the stack under these conditions, thus they settle towards the ground due to turbulence and mixing.
- As a result, the dispersion of contaminants in a fumigant plume is exceedingly poor.
Trapping Plume
In air pollution meteorology, a trapping plume occurs between two inversion layers, confining pollutants within a specific altitude, showcasing a critical plume behavior.
- When an inversion layer exists above and below the stack, the plume does not rise or fall.
- Rather, it is constrained or trapped between the two inversion levels, resulting in a trapping plume.
- This plume isn’t optimal for pollution dispersion since it can’t go past a particular height.
Key take aways
That’s it about air pollution meteorology. Hope you found it insightful.