The average composition of dry, pure air in the layer of the atmosphere up to an altitude of 25 km is summarized in Table 3. Traces of other gases (carbon monoxide [CO], radon [Rd], nitrous oxide [N2O], methane [CH4], ammonia [NH3], and various hydrocarbons) occur also and are important beyond their low concentrations. Many of these are greenhouse gases and play a significant role in the radiative equilibrium of the Earth-Atmosphere system. In fact, the most important gases from a meteorological standpoint are the minor gases, with nitrogen and oxygen providing little but a bulk pressurizing service and service to life.
Above 80 km oxygen is dissociated on absorption of ultraviolet radiation from the sun. At higher levels nitrogen is also dissociated. While the dissociation products are not significant from the stand point of the dynamics of the atmosphere they are critical to the layering of the atmosphere. The dissociated ions form the layers off which we bounce our radio waves for long distance communication.
Dust, smoke, salt particles, condensed liquid and solid water are the most abundant nongaseous material found in the atmosphere. These materials affect the transmission of incoming solar radiation as well as outgoing terrestrial radiation. These particles are of critical importance in cloud processes and in the realization of precipitation from these clouds.
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