Atmospheric Chemistry: The Present Day Atmosphere


The atmosphere we breathe is a relatively stable mixture of several hundred types of gases from different origins. The proportions of gases, excluding water vapor, are nearly uniform up to approximately 80 kilometers (km) above Earth's surface. The major components of this region, by volume, are oxygen (21%), nitrogen (78%), and argon (0.93%). Small amounts of other gases are also present.
[These remaining trace gases exist in such small quantities that they are measured in terms of a mixing ratio.....parts per million by volume (ppmv), parts per billion by volume (ppbv) or parts per trillion by volume (pptv).]
Atmospheric temperature and chemistry are believed to be controlled by the trace gases. [There is increasing evidence that the percentages of environmentally significant trace gases are changing because of both natural and human factors.]

Purely man-made gases include chlorofluorocarbons CFC-11 and CFC-12 and halons. Carbon dioxide, nitrous oxide, and methane (CH4) are produced by the burning of fossil fuels, and some natural sources.

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