2. Basics of air ions (2)
A. How are air ions created?
A. How are air ions created?
Air ions in the atmosphere are generated in various ways.
While new ions are generated some cease to exist in order to maintain a certain balance.
(1) UV rays
Gaseous molecules are intensively ionized when UV rays pass through the molecules.
(Research conducted by Leonard, Thompson, Brenry)
This intensive ionization phenomenon can be found in the upper layers of the atmosphere.
It has been said that molecules are ionized about 10 times more intensively at an altitude of 10km than at the ground surface.
These highly concentrated ions are diffused to the ground surface at low speeds.
Negative and positive ions combine together and they are electrically cancelled out on their way back to the ground surface. This results in lower ion densities at or near the earth's surface.
(2) Lenard's effect (Waterfall effect)
When a drop of water changes its shape (e.g. splits into smaller droplets),
the droplets and the surrounding air are charged positively and negatively respectively.
This is the Lenard's effect.
Two electronic layers always exist on the surface of a drop of water.
The inner/outer layer is charged negatively/positively respectively.
As soon as a newly formed water droplet has contact with the air positive ions in the air are absorbed into the droplets outer layer.
As a result the surrounding air is charged negatively and thus negative air ions are generated.
Ions are generated by the photoelectric effect (when a light of a certain wavelength hits a metallic surface, the surface emits electrons).
Electrons collide with molecules in the air to ionize the molecules.
It has been said that the photoelectric effect is less likely to cause ion generation because few substances, which can cause the photoelectric effect, exist at or near the surface of the earth.
(4) Radioactive substance
The majority of ions found at or near the surface of the earth are generated by alpha, beta or gamma rays.
(A) Alpha ray
This ray is positively charged.
A helium atom becomes a positively charged tiny particle after losing two electrons.
When the particle passes through the air it collides with gaseous molecules and ionizes them intensively.
(B) Beta ray
This is an electron and it is charged negatively and it passes through the air at very high speeds.
It does not ionize other molecules so intensively as the alpha ray.
(C) Gamma ray
This is a very short wavelength electromagnetic wave.
Its transmittance is higher than that of X rays while it ionizes molecules as intensively as the X ray.
(5) Radium emanation
The radioactive series (e.g. Uranium, Radium, Actinium, Thorium) exist extensively in the earth.
"Emanation" is a gaseous form of decayed substances found at the surface of the ground.
It decays more rapidly in the atmosphere while emitting alpha, beta and gamma rays, and it ionizes the air.
Negative ions are generated when atmospheric pressure falls because air is drawn out of the earth together with Emanation due to the pressure changes.
(6) Ion balance in the atmosphere
In most cases, positive and negative ions are generated in pairs.
While few ways generate positive ions only, the Lenard's effect, beta ray emission and so on generate negative ions only.
In theory, more negative ions should exist in the air.
However, negative ions decrease by recombination as the air gets polluted.
Author: Masaharu Nemoto
(Universal Plan Co., Ltd.)
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