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Original artwork by Windows to the Universe staff (Randy Russell).
Related links:
MILAGRO Campaign - studying air pollution around Mexico City
Movie showing when gases will rise and mix and when they won't
Tropospheric Ozone, The Polluter content and activities from Project LEARN
The Troposphere
The troposphere is the lowest layer of Earth's atmosphere. The troposphere starts at ground level. The top of the troposphere is about 11 km up (that's 7 miles or 36,000 feet). The layer above the troposphere is called the stratosphere.
Most of the air (about 3/4ths) in our atmosphere is in the troposphere. Almost all weather happens in the troposphere. Most clouds are found in this lowest layer, too. The jet stream is near the top of the troposphere. This "river of air" zooms along at 400 km/hr (250 mph)!
The troposphere is warmest near the ground. Sunlight heats the ground (or oceans!). The ground heats the air that is closest to it... at the bottom of the troposphere. The higher up you go in the troposphere, the colder it gets. That's why there is often snow in tall mountains, even in the summer. The temperature at the top of the troposphere is around -55° C (-64° F)! Brrrrrrrrr!
Air also gets 'thinner' as you go higher up. That's why mountain climbers sometimes need bottled oxygen to breathe.
The "border" between the troposphere and the stratosphere above it has a special name. It is called the tropopause. The height of the tropopause actually depends on whether it is day or night, summer or winter, or whether you are near the equator or one of the poles. At the equator, the tropopause is about 20 km (12 miles or 65,000 feet) above sea level. In winter near the poles the tropopause is much lower. It is about 7 km (4 miles or 23,000 feet) high.
