AWH 4-2

Chapter 4, The Earth’s Atmosphere 4-2 4.2 Composition The Earth’s atmosphere consists of numerous gases (see Table 4-1) with nitrogen, oxygen, argon, and carbon dioxide making up 99.998 percent of all gases. Nitrogen, by far the most common, dilutes oxygen and prevents rapid burning at the Earth’s surface. Living things need it to make proteins. Oxygen is used by all living things and is essential for respiration. Plants use carbon dioxide to make oxygen. Carbon dioxide also acts as a blanket and prevents the escape of heat to outer space. Table 4-1. Approximations of the Composition of a Dry Earth’s Atmosphere Gas Symbol Content (by Volume) Nitrogen N2 78.081% Oxygen O2 20.945% Argon Ar 0.932% Carbon Dioxide CO2 0.042% Neon Ne 18.20 parts per million Helium He 5.20 parts per million Methane CH4 1.75 parts per million Krypton Kr 1.10 parts per million Sulfur Dioxide SO2 1.00 parts per million Hydrogen H2 0.50 parts per million Nitrous Oxide N2O 0.50 parts per million Xenon Xe 0.09 parts per million Ozone O3 0.07 parts per million Nitrogen Dioxide NO2 0.02 parts per million Iodine I2 0.01 parts per million Carbon Monoxide CO trace Ammonia NH3 trace Note: The atmosphere always contains some water vapor in amounts varying from trace to about 4 percent by volume. As water vapor content increases, the other gases decrease proportionately. Weather (the state of the atmosphere at any given time and place) strongly influences daily routine as well as general life patterns. Virtually all of our activities are affected by weather, but, of all of our endeavors, perhaps none more so than aviation.