Page 288 - Fundamentals of Air Pollution

244 17. The Physics of the Atmosphere

Fig. 17-1. Electromagnetic spectrum. Note the regions of solar and earth radiation.

processes. The earth's gravity keeps the thin layer of gases that constitute
the atmosphere from escaping. The combination of solar heating and the
spin of the earth causes internal pressure forces in the atmosphere, resulting
in numerous atmospheric motions. The strength of the sun's radiation, the
distance of the earth from the sun, the mass and diameter of the earth,
and the existence and composition of the atmosphere combine to make the
earth habitable. This particular combination of conditions would not be
expected to occur frequently throughout the universe.
As noted in Chapter 2, the atmosphere is approximately 76% nitrogen,
20% oxygen, 3% water, 0.9% argon, and 0.03% carbon dioxide; the rest
consists of relatively inert gases such as neon, helium, methane, krypton,
nitrous oxide, hydrogen, and xenon. Compared with the average radius
of the earth, 6370 km, the atmosphere is an incredibly thin veil; 90% is
below 12 km and 99% below 30 km. In spite of its thinness, however, the
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total mass of the atmosphere is about 5 x 10 kg. Therefore, its heat
content and energy potential are very large.

A. Radiation from a Blackbody
Blackbody is the term used in physics for an object that is a perfect emitter
and absorber of radiation at all wavelengths. Although no such object exists