Air is made up of molecules. Each molecule has a core, or nucleus, of positively charged protons surrounded by negatively charged electrons. In a stable atmosphere, nature seeks a balance in which there are as many electrons as protons so that the positive and negative charges cancel one another out. Electrons, being considerably lighter than protons are easily displaced — and when this happens the equilibrium is upset — ions are created. The displaced electrons which then become negatively charged, attach themselves to normal molecules, such as dust particle, and causes them to cling to room surfaces rather than float freely in the air.

The discovery of ions is attributed to Jean Antoine Nollet (1700-70), a French abbe and physicist, who also discovered osmosis, invented an electroscope and improved the Leyden jar.

In 1775, Father Gina Battista Baccaria of the University of Turin, Italy, wrote:


In the 1890s, scientists found that this air electricity comes from charged molecules — or ions — of gas. It was not until the 1920s however, that researchers took seriously the claims of the natural philosophers who argued that air electricity was in fact a vital part of the process that creates and sustains life.

These proponent ideas led to the invention of negative ion generators to purify the air by neutralising positive ions with negative ions. An abundance of positive ions is believed to increase levels of serotin in the nervous system leading to depression and irritability. Proponents of negative ion therapy (aeroiontherapy) claim that illness can be prevented by using these generators. However, these devices cannot produce enough ions to change the air in a room effectively, and scientific studies over many years have failed to support the claims made on their behalf.

In 1977, Fred Soyka, a principal proponent of negative ionisation, wrote a book, The Ion Effect, extolling its benefits. A review by Warner Clements in the Skeptical Inquirer takes the author to task, pointing out the many errors and contradictions in the book, and for failing to point out that ion generators also generate ozone. Ozone is toxic, and was a factor in the demise of early consumer-type air ionisers in the 1950s.


References:

American Medical Association, 1993. Alternative Health Methods. American Medical Association. Chicago.

Barrett, Jarvis, Kroger & London. 1997. Consumer Health: A Guide to Intelligent Decisions. Brown & Benchmark Publishers.

Clements, Warner. 1980. The Ion Effect, a book review. Skeptical Inquirer, Vol. 4 No.3, p.66-68.

Krueger, AP. 1973. Are Air Ions Good for You? New Scientist. UK. June 14, 1973.

----------------  1963 Influences of Air Ions on Certain Physiological Functions, Medical Biometeorology—Weather Climate and the Living Organism. Elsevier, Amsterdam, N.Y.

Soyka, Fred. 1977. The Ion Effect, Bantam Books Inc.