Atmospheric Composition Encyclopedia of Aerospace Engineering, 9 Volume Set
This article considers the gases constituting Earth’s atmosphere and how the mixture of atmospheric gases varies with altitude up to roughly 1,000 km. Turbulent mixing keeps the relative concentrations of gases nearly constant in the lowest 100 km. At higher altitudes, molecular diffusion controls the concentrations, with the lighter gases becoming relatively more abundant with increasing altitude. Atmospheric gases are electrically neutral up to about 60-km altitude. At higher altitudes, energetic solar radiation from the sun ionizes neutral molecules, creating charged particles (ions and free electrons), which mix with the neutral particles.