U.S. Dept. of Agriculture
A recent study by the U.S. Dept. of Agriculture found that ionizing a room led to 52% less dust in the air, and 95% less bacteria in the air (since many of the pollutants found in the air reside on floating dust particles).

Agriculture Research Service (of USDA)
The Agriculture Research Service of the U.S. Dept. of Agriculture tested the effectiveness of ionizers for removing dust in a poultry hatchery. The dust level is very high in such an environment. In this study, the use of an ionizer resulted in dust removal efficiencies that averaged between 81.1 and 92.2%. The airborne transmission of salmonella (to the eggs) was also significantly reduced as a result.

See Link: http://www.nalusda.gov/ttic/tektran/data/000008/54/0000085456.html

Journal of Hygiene
Scientists showed that ionization reduced bacterial levels in burns and plastic surgery units by over 96% after a two week period, which results in much better and more rapid healing of patients.

Journal of Applied Microbiology
The use of negative ions was even found by scientists to reduce the presence of airborne viruses by about 40%. A study featured in the 1987 issue also showed the negative ions are free from any adverse side effects.