Studies and research on negative ions goes a long way back in the 1900s. One of the earliest research was conducted by none other than Albert Einstein. In 19l0, along with a colleague, Conrad Harbicht - took as a Ph.D. thesis, the problem of why the mountain air of Davos was renowned for its health-giving properties.

They decided it was "Air Electricity". Einstein went on to consider other matters, but Harbicht later raised funds to continue his research and the first ionizers were built.

In the 1940s and 1950s, the U.S. Air Force did more research on negative ions. Pilots usually passed out at high altitudes. When tested, the air in the planes was found to be hight in positive ions. When negative-ion generators were placed in the planes, pilots stayed awake and alert.

Below are some links to additional research/studies done, notably the 1 year study/research in St James's Hospital in Leeds, study no. #2

1.	Negative Air Ionization - Penn State Univ. Aero-biological Engineering, Negative air ionization has the potential to reduce the concentration of airborne microorganisms. The effect appears to result from the ionization of bioaerosols and dust particles that may carry microorganisms, causing them to settle out more rapidly.
2.	Air ionizers wipe out hospital infections New Scientist, Jan 2003 Repeated airborne infections of the bacteria acinetobacter in an intensive care ward have been eliminated by the installation of a negative air ioniser. In the first such epidemiological study, researchers found that the infection rate fell to zero during the year long trial. "We were absolutely astounded to find such clear cut results," engineer Clive Begg at the University of Leeds, UK, told New Scientist.
3.	Pharmacy and Health: Ionized Air The Kroger Company (NYSE:KR) Ionized air may play a role in allergies. Research suggests that some allergy-provoking substances, such as dust and pollen, have a positive electrical charge. Negative ions appear to counteract the allergenic effects of these positively charged ions on respiratory tissues. Negative ions also have other beneficial effects for the respiratory system.
4.	Negative Ions and Health - Swiss Meteorological Institute. In 1974, the Swiss Meteorological Institute first studied problems related to seasonal winds in various regions of the earth. The Foehn that blows across Switzerland, the Sirocco in Italy, the Sharav in the Middle East, and the Mistral in southern France were determined to cause physical and mental effects ranging from headaches and depression to heart attacks. The one common denominator in all these wind variants was the type of electrical charge of the ions in the air. A very high concentration of positive ions was found to be the culprit. Conversely, the air quality studied at the site of a waterfall, in the mountains, or after a spring rain showed significant amounts of negative ions. Further research revealed that human beings respond to negative ion levels above 1000 ions per cc. Scientific research concluded that negatively charged ions have positive effects on living organisms. Plants grow faster and healthier, lab animals are calmed and more able to perform certain tasks, and humans respond with increased alertness and relaxation.
5.	Ions and Computers - Geophysical Institute, University of Alaska Fairbanks Evidence shows that the new trend towards using computerized equipment in offices may be creating a special problem. One experiment performed in England on 54 individuals at a computer site seems rather convincing. Negative-ion generators were installed, but, unknown to the persons being tested, the generators were not turned on for four weeks. During that period the negative-ion concentration was about 550 per cubic cm. A secret switching on the generators during the next eight weeks of the test raised the ion concentration to 3,500 per cubic cm, several times that found in normal outside air. After the experimenters turned on the ion generators, they found that the tested persons had fewer headaches and other complaints than before. Only five percent then said they had headaches, whereas 20 percent of the workers complained of headaches before the ion generators were turned on. The number reporting dizziness and nausea dropped by more than half, down to less than one percent.