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A short class with Sarah and her students. The other ways are under More.
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Today, we're going to learn about the temperature profile of air and how it affects pollutant transport. Can anyone tell me what happens to temperature as we go higher in the atmosphere?
I think the temperature gets colder as you go up?
That's right! This is part of what we call the environmental lapse rate. So, if the temperature decreases with height, what might happen to warm air rising from a source, like a diesel generator?
It would rise because it's warmer than the surrounding air.
Exactly! This process is called buoyancy. Can anyone remember the typical rate at which temperature decreases with height?
Is it around 9.8 degrees Celsius per kilometer?
Yes, that's the dry adiabatic lapse rate! It’s crucial for understanding how pollutants disperse.
Now let's consider atmospheric stability. Who can tell me what happens in a stable environment?
In a stable environment, warm air can't rise because it's cooler than the surrounding air.
Correct! That means pollutants will be trapped close to the surface, which is not good for air quality. What about unstable environments?
In an unstable environment, warm air can rise easily, so pollutants spread out more.
It depends more on the wind for movement of pollutants, right?
Spot on! This is why we study these concepts—understanding stability helps us manage air quality effectively.
We’ve talked about how buoyancy and stability influence pollutant dispersion. Now, what critical factor do we use to describe where this mixing happens?
Mean mixing height?
Yes! The mean mixing height indicates how pollutants can be diluted in the atmosphere. What happens if we have a low mixing height?
There would be higher concentrations of pollutants because there's less room to disperse!
Exactly! And that's a core reason we monitor these profiles—so we manage air quality effectively.
The rate of temperature decrease with rising altitude.
The force causing warm air to rise, leading to pollutant dispersion.
A constant rate of temperature change for rising air without heat exchange.
The tendency of the atmosphere to either allow or inhibit vertical air motion.
During the day, ground temperatures can reach up to 35°C while the air may be only 25°C. This creates a temperature gradient that leads to buoyancy and rising air.
In winter, a temperature inversion might occur where the air near the ground is cooler than the air above, trapping pollutants at the ground level.
As the temperature rises, warm air flies, polluting skies when stability sighs.
Once there was a warm bubble, rising up high, but in a stable world, it would not fly, trapped under clouds, it sighed, wondering why.
B.U.D. - Buoyancy, Unstable, Dispersion.
M.E.R. - Mixing height, Environmental lapse rate, and Release of pollutants.
Term
What is the environmental lapse rate?
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Term
What happens in a stable atmosphere?
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The variation of temperature with height in the atmosphere.
The rate at which temperature decreases with height in the atmosphere.
The rate at which a rising air parcel cools without heat exchange, typically at -9.8 °C/km.
The tendency of a warm air parcel to rise due to being lighter than the surrounding cooler air.
A measure of an air mass's ability to resist vertical motion.
The height at which pollutants can be effectively mixed with the surrounding atmosphere.
This section discusses the temperature profile of air as a function of height, introducing concepts of buoyancy, adiabatic lapse rates, and the impact of atmospheric stability on pollutant transport.
The section explores how temperature differentials create thermal forces, leading to vertical convection of air masses. It also covers the dry adiabatic lapse rate, environmental lapse rate, and the impact of stable, neutral, and unstable atmospheric conditions on the transport and concentration of pollutants.
This section delves into the phenomenon of vertical convection in the atmosphere, primarily influenced by temperature gradients as a function of height. It explains how the temperature profile changes throughout the day as surfaces heat up or cool down, creating distinct thermal layers.
The concept of buoyancy is introduced, indicating that warmer air parcels tend to rise, aided by thermal forces in an unstable environment, while cooler air sinks. The dry adiabatic lapse rate (approximately -9.8 °C per kilometer) is discussed towards understanding how temperature decreases with height in a rising air mass when no heat is exchanged with the environment.
Furthermore, the environmental lapse rate is contrasted with the dry adiabatic lapse rate, highlighting how this difference informs atmospheric stability and, consequently, the dispersion of pollutants. Stability in the atmosphere is classified into three types:
The section culminates with the importance of mean mixing height for understanding air quality management, emphasizing that inadequate vertical mixing can lead to increased pollutant concentrations.