Thermal Inversion
Introduced| English | Meaning |
|---|---|
| lid/lɪd/ | lid |
| thermal inversion/ˈθɜːml ɪnˈvɜːʃn/ | thermal inversion |
| inversion/ɪnˈvɜːʃn/ | inversion |
A lid on the air
- Normally, air near the warm ground rises and carries pollution away.
- Sometimes this stops working, and smog just sits there.
- The cause is a thermal inversion 逆温现象.
- It puts a warm lid over a city and traps the dirty air.
The normal case
- Usually the air gets colder as you go higher.
- Warm air near the ground is lighter, so it rises.
- Rising warm air carries pollution up and away.
- The air near the ground stays fairly clean.
A thermal inversion 逆温: warm air above cool air traps pollution near the ground
In a thermal inversion, the unusual thing is that…
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Normally air cools with height. In an inversion, a warm layer sits on top of cooler air — upside down.
The inversion
- In an inversion, a layer of warm air sits above the cool air.
- This is upside down from normal — hence "inversion".
- The warm layer acts like a lid 盖子 on the cool air below.
- Cool, polluted air cannot rise through it and escape.
How a thermal inversion traps pollution
See how a warm-air lid stops polluted air from rising and clearing away.
A thermal inversion makes air pollution…
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The warm lid stops polluted air from rising and clearing, so smog builds up near the ground.
The warm air layer acts like a ____ that traps pollution below it.
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The warm layer is a lid — cooler polluted air cannot rise through it and escape.
Pollution piles up
- With no way to rise, pollution builds up near the ground.
- Smog grows thicker hour by hour under the lid.
- Cities in valleys are hit hardest — hills hold the cool air in.
- The smog clears only when the weather breaks the inversion.
Cities in valleys are protected from temperature inversions by the surrounding hills.
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False. Surrounding hills trap the cool air layer and its pollution, so valley cities often suffer worse inversions.
Select all true statements about thermal inversions.
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An inversion puts warm air on top, trapping pollution and worsening smog. It does not clear the air.
The whole trick is the reversed temperature order. Normal air: cold on top, warm below → warm air rises → pollution disperses. Inversion: warm on top, cool below → the cool air (and its pollution) can't rise through the warm lid → smog is trapped. An inversion doesn't make pollution; it stops pollution from clearing.
A valley city in winter:
- Cold air pools in the valley overnight; a layer of warm air settles above it.
- Morning traffic and heating pump pollution into that trapped cold air.
- The warm lid holds it all down, and with hills blocking the wind, the smog thickens for days — until a storm finally mixes the air and clears it.
A thermal inversion flips the usual pattern: a layer of warm air sits above cooler air, acting as a lid. Cool, polluted air near the ground cannot rise through it, so smog is trapped and builds up. Inversions make air pollution far worse, especially in cities ringed by hills.