ABSTRACT
The atmosphere consists of the thin layer of mixed gases covering the Earth’s surface. Exclusive of water, atmospheric air is 78.1% (by volume) nitrogen, 21.0% oxygen, 0.9% argon, and 0.04% carbon dioxide. Normally, air contains 1%–3% water vapor by volume. In addition, air contains a large variety of trace-level gases below 0.002%, including neon, helium, methane, krypton, nitrous oxide, hydrogen, xenon, sulfur dioxide, ozone, nitrogen dioxide, ammonia, and carbon monoxide. The atmosphere behaves as it does as a consequence of the gases in it from both natural and anthropogenic sources and the physical forces acting on it.
