The Composition of The Atmosphere

The atmosphere consists essentially of a mixture of gases. Within these gases, tiny solid particles of dust and smoke are suspended. In addition, water occurs not only as a vapor but also in solid and liquid forms.

The composition of dry air by volume at sea level at locations remote from large cities and forest fires are:

  • Nitrogen: 78%
  • Oxygen: 21%
  • Other gases: 1%

In general gases of the atmosphere are present in the same proportions up to an altitude of about 80 km. However, there are some important exceptions such as water vapor, ozone, and carbon dioxide. These gases are found in the following quantities in the lower levels of the troposphere:

  • Water vapor: 0 to 5%, essential for cloud formation and is the main source of the greenhouse effect;
  • Carbon dioxide: 0.037%, absorbs infrared (IR) radiation and contributes to the greenhouse effect;
  • Ozone: 0.001%, toxic and very reactive. Low-level ozone is the main gaseous constituent of airborne pollution.
Water vapor is the most important gas as far as meteorology is concerned. The amount of water vapor in the air (often expressed as humidity) varies greatly between the oceans and deserts, between ground level and higher altitudes, and between cold and hot regions. Even though water vapor makes up only a small percentage of the atmosphere, the energy released/consumed as it changes from gas to liquid to ice and back again, drives many severe weather systems such as thunderstorms, tornadoes, and cyclones.

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