10.6: Troposphere

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What if we took a field trip to the troposphere?

A field trip to the troposphere could start below sea level in Badwater Basin in Death Valley. It could end at the top of Mt. Everest at 29,029 feet (8,848m). In other words, every human activity that's in air is in the troposphere. You might say that your life is a field trip to the troposphere!

Troposphere

The troposphere is the lowest layer of the atmosphere. All of the air you breathe is in the troposphere. All of Earth's weather—wind, rain, snow, heat—is in the troposphere. The troposphere is the lowest and most important layer of the atmosphere!

Properties of the Troposphere

The troposphere is the shortest layer of the atmosphere. It rises to only about 12 kilometers (7 miles) above the surface. Even so, this layer holds 75% of all the gas molecules in the atmosphere. That’s because the air is densest in this layer.

In the troposphere, temperature decreases with altitude. The troposphere gets some of its heat directly from the Sun. Most, however, comes from Earth's surface. The surface is heated by the Sun. Some of that heat radiates back into the air. This makes the temperature higher near the surface than at higher altitudes.

Mixing of Air

Air in the troposphere is warmer closer to Earth’s surface. Warm air is less dense than cool air, so it rises higher in the troposphere. This starts a convection cell. Convection mixes the air in the troposphere. Rising air is also a main cause of weather. All of Earth’s weather takes place in the troposphere.

Temperature Inversion

Sometimes air doesn’t mix in the troposphere. This happens when air is cooler close to the ground than it is above. The cool air is dense, so it stays near the ground. This is called a temperature inversion (Figure below). An inversion can trap air pollution near the surface. Temperature inversions are more common in the winter. Can you explain why?

Diagram of a temperature inversion

Temperature Inversion and Air Pollution. How does a temperature inversion affect air quality?

Tropopause

At the top of the troposphere is a thin layer of air called the tropopause. This layer acts as a barrier. It prevents cool air in the troposphere from mixing with warm air in the stratosphere.

Summary

In the troposphere, warm air ordinarily sits below cooler air.
With a temperature inversion, cold air sits below warm air. This traps the cold air because it cannot rise into the warm air.
An inversion starts over land at night or in the winter, or near the coast.

Review

Why is the troposphere the most important layer of the atmosphere?
What is the source of heat in the troposphere?
Describe the temperature gradient found in the troposphere.