Various industrial pollutants also may be present as gases or aerosols, such as chlorine (elemental or in compounds), fluorine compounds and elemental mercury vapor.Sulfur compounds such as hydrogen sulfide and sulfur dioxide (SO Earth's atmosphere Lower 4 layers of the atmosphere in 3 dimensions as seen diagonally from above the exobase.The exosphere is located too far above Earth for any meteorological phenomena to be possible.

By volume, dry air contains 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, and small amounts of other gases.

Air also contains a variable amount of water vapor, on average around 1% at sea level, and 0.4% over the entire atmosphere.

The concentration of water vapor (a greenhouse gas) varies significantly from around 10 ppm by volume in the coldest portions of the atmosphere to as much as 5% by volume in hot, humid air masses, and concentrations of other atmospheric gases are typically quoted in terms of dry air (without water vapor).

among which are the greenhouse gases, principally carbon dioxide, methane, nitrous oxide, and ozone.

Layers drawn to scale, objects within the layers are not to scale.

Aurorae shown here at the bottom of the thermosphere can actually form at any altitude in this atmospheric layer.Because the general pattern of the temperature/altitude profile is constant and measurable by means of instrumented balloon soundings, the temperature behavior provides a useful metric to distinguish atmospheric layers.In this way, Earth's atmosphere can be divided (called atmospheric stratification) into five main layers.Thus, the exosphere no longer behaves like a gas, and the particles constantly escape into space.These free-moving particles follow ballistic trajectories and may migrate in and out of the magnetosphere or the solar wind.This layer is mainly composed of extremely low densities of hydrogen, helium and several heavier molecules including nitrogen, oxygen and carbon dioxide closer to the exobase.