Thermal inversion is

• A. A weather condition where warm air traps cooler polluted air near the ground.
• B. A weather condition in which the upper atmosphere has lower pressure.
• C. A layer of the atmosphere that contains no pollution.
• D. A seasonal rainfall pattern.

Answer: (C)

Thermal inversion happens when a layer of warmer air sits above cooler air near the ground, creating a lid that prevents vertical mixing. Because the air near the surface stays cool and stagnant while aloft is warmer, pollutants emitted at ground level get trapped and concentrations can build up, leading to smog and poor air quality in affected areas.

The other choices don’t match this mechanism. It isn’t about lower pressure in the upper atmosphere, which describes a different atmospheric condition. It isn’t about a layer that contains no pollution—an inversion often leads to higher pollutant buildup near the ground. And it isn’t related to a seasonal rainfall pattern, which is a weather phenomenon independent of temperature layering and air mixing.