Ions, Atmospheric

Ions, Atmospheric

 

electrically charged particles in the atmosphere. They form in the upper atmospheric layers mainly because of the action of ultraviolet and corpuscular radiation from the sun, as well as in lower atmospheric layers (the troposphere and stratosphere) as a result of radioactive radiation and cosmic rays, which cause ionization of neutral molecules or atoms. As a result, free electrons and positively charged molecules or atoms—positive ions—are formed. The free electron almost instantaneously combines with a neutral molecule or atom, forming a negative ion. These so-called monomolecular ions exist under ordinary conditions in the lower atmospheric layers for a very short time, since several neutral gas molecules attach to the ions virtually instantaneously, thus forming fairly stable molecular complexes. Each atmospheric ion is usually assumed to carry a single elementary charge. Atmospheric ions are arbitrarily divided into three groups according to the value of the mobility K, which is the mean rate of migration in an electric field with the intensity of 1. (See Table 1.)

Table 1
 Mobility K (cm2/sec · V)Ionic radius r (multiplied by 108 cm)
Light...........>1< 7-8
Medium.........1 > K > 0.018 < r < 80
Heavy and ultraheavy....< 0.01> 80

“Ordinary” atomic and molecular ions are found in the upper atmospheric layers. The lower atmospheric layers contain light ions in the form of complexes of gas molecules (up to several dozen), as well as medium and heavy ions. Heavy ions usually appear upon precipitation of light ions on very small liquid or solid particles suspended in the atmosphere. Some of these ions may form upon evaporation of larger charged particles. The mean concentration of atmospheric ions is determined by the balancing of their rates of formation and by their rate of disappearance as a result of recombination and conversion into heavier particles. The average lifetime of a light atmospheric ion is several dozen or even hundreds of seconds, whereas that of a heavy atmospheric ion is several thousand seconds.

Pure air near the earth’s surface contains about 500–1,000 light ions per cu cm, and there are 10–20 percent more positively charged particles than negatively charged particles. The concentration and mobility of light ions in the troposphere increase with altitude; for example, at an altitude of 10 km their concentration may exceed the quantity mentioned above by a factor of about 10. The concentration of heavy ions increases with increasing concentration of nuclei in the atmosphere. The concentration of heavy ions may reach ~ 100,000 per cu cm in cities and industrial areas. Under these conditions, as the concentration of heavy ions increases, the concentration of light ions decreases (it may fall to ~ 10 per cu cm). The concentrations of light and heavy ions are not identical in different geographic locations, and they may also vary diurnally, as well as annually. The concentration of light ions is usually highest early in the morning and lowest at midday; there are more light ions in summer than in winter. The concentrations of atmospheric ions in certain areas may differ markedly from the average values over the entire earth. Many atmospheric ions are generated near waterfalls and fountains, as well as during corona discharge involving sharp objects in strong electric fields (for example, during thunderstorms or dust storms). The electric conductivity of air, which depends mainly on the number of light ions, varies with their concentration. The presence of atmospheric ions has a marked effect on human physiology in the course of many diseases. Whereas greater quantities of negatively charged ions stimulate human activity, greater quantities of positive ions lead to high susceptibility to fatigue and the appearance of headaches and other effects. Effects of ions on the life processes of animals and plants have been observed.

The concentration of atmospheric ions may be measured using so-called ion counters; the concentration distribution according to ion mobility is determined by means of ion spectrometers.

REFERENCES

Tverskoi, P. N. Atmosfernoe elektrichestm. Leningrad, 1949.
Imianitov, I. M. Pribory i metody dlia izucheniia elektrichestva atmosfery. Moscow, 1957.
Minkh, A. A. Ionizatsiia vozdukha i ee gigienicheskoe znachenie. Moscow, 1958.

I. M. IMIANITOV

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