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The troposphere begins at the Earth's surface,
which acts as a source of heat resulting from absorption of
visible sunlight. The temperature decreases with height in the
troposphere, and so the air is well mixed in this region (Greek:
tropos a turning). Weather phenomena such as thunderstorms and
clouds occur in this layer, as does most of the commercial airline
traffic at present (exceptions include the higher-flying supersonic
aircraft, for example, the Concorde). About 6 to 10 miles (10
to 17 kilometers) above the Earth, a new region called the stratosphere
begins. The stratosphere is heated from above (absorption of
solar ultraviolet radiation by oxygen and ozone) and temperature
increases with altitude. In this region there is much slower
mixing (Latin: stratum, layer). The "ozone layer"
resides in the stratosphere. At about 30 miles (50 kilometers),
temperature begins to decrease with altitude again and the mesosphere
begins.
Both the stratosphere and the troposphere
have important direct and indirect effects on the well-being
of humankind. In this century, it has become increasingly clear
that humans are influencing the chemical composition of the
troposphere and stratosphere in ways that can impact conditions
at the Earth's surface. Some of the most challenging environmental
issues of our time have arisen, and thus the need for ozone
research and monitoring has become very important.
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