troposphere

Here, well above the troposphere, the air was thin and always clear.

Investigators have noted the importance of rain or snow in washing fallout particles from the air in the troposphere.

The dense reaches of the troposphere—the weather belt where storms are born—dropped below them.

At last Ken leveled off in the troposphere, at an altitude of five miles.

In distinction from the stratosphere, the part of the atmosphere lying below it is called the troposphere.