APES 7.3 Thermal Inversion

Enduring Understanding:

• Human activities have physical, chemical, and biological consequences for the atmosphere.

Learning Objective:

• Describe thermal inversion and its relationship with pollution.

Essential Knowledge:

• During a thermal inversion, the normal temperature gradient in the atmosphere is altered as the air temperature at the Earth’s surface is cooler than the air at higher altitudes.
• Thermal inversion traps pollution close to the ground, especially smog and particulates.

Thermal Inversion

• Under normal conditions in the troposphere, temperature decreases as altitude increases
• During thermal inversion, there is a reversal in the trend
  • A warmer layer on top of the cooler surface air develops
  • This is the opposite of the expected conditions
• Thermal inversion ‘traps’ cooler, denser air
  • Air cannot rise, so pollutants do not disperse
  • This includes photochemical smog and particulate matter
• Geography can encourage inversion layers
  • Valleys, near mountain ranges, and coastal or prevailing winds increase the frequency of inversion layers
• Pollution is intensified by the inversion
  • Large cities with high industrialization and many vehicles will be more affected by inversion

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