For more than ten years, controversy has swirled around the usefulness of ion generators sold (at roughly 100 dollars each) to improve air quality in homes and offices. Total American sales of ion generators was near the ten million dollar mark in 1980, so obviously many people think or hope the generators are worthwhile.

The stated purpose of a home or office ion generator is to increase in the air the number of molecules or molecular clusters that carry positive or negative charges - such molecules or clusters are called ions, even though the name ion has a broader meaning for most scientists.

Any volume of natural air near the earth's surface contains roughly equal numbers of positive and negative ions, there being about a thousand or so of each in a cubic centimeter of natural air. Since there are more than ten billion billion air molecules per cubic centimeter, the ratio of ions to neutral air molecules is pretty small.

The relatively few ions that do exist in the air are created mostly by decay of radioactive materials in the earth's crust and by cosmic rays striking the air. Because more cosmic rays come into the polar regions than the tropics, there is tendency for higher ion concentrations in the air at high latitude.

Such a trend bodes well for those of us who live in the North, if it is really true, as many claim, that high ion concentrations make for a better living environment. It certainly is true that in urban areas where air pollution is severe the concentration of ions in the air is very low. In an urban office the ions may number as few as fifty per cubic centimeter.

Ions attach to pollution particles and may assist in sweeping the pollution particles out of the air by interacting with electric fields that exist naturally in the air. If that really happens as claimed, then an effective ion generator is useful. It is also argued that the existence of high ion concentrations in air promotes plant growth, inhibits bacterial growth and generally makes people feel better. Clearly this is one of those issues needing further investigation.

This column is provided as a public service by the Geophysical Institute, University of Alaska Fairbanks, in cooperation with the UAF research community. T. Neil Davis is a seismologist at the institute.

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