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| 1.6 SUMMARY Nitrogen, oxygen, argon, carbon dioxide, and small amounts of other gases make up the air surrounding the earth. The amount of water vapor in the air depends upon the temperature of the air. Impurities in the air are important because of their effect on visibility and the fact that they are necessary for forming clouds and condensing water vapor. Air has weight and is in layers surrounding the earth. The layers, starting with the one next to the earth, are the troposphere, stratosphere, ionosphere, and exosphere. The tropopause is a narrow area between the troposphere and the stratosphere. The jet stream is near the upper portion of the troposphere. As altitude is increased, temperature decreases at an average lapse rate of 2°C or 3 1/2°F per thousand feet. As temperature increases or altitude becomes higher, wings and rotor blades become less efficient. Density altitude must be evaluated before takeoffs or landings can be accomplished safely. |
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Last Updated: January 10, 2009