Searching the web for air ionizers will return little substance. What you'll find is marketing hype from manufacturers of in-room ionizers.
Ionization can charge particles, but unless these charged particles are captured on a media filter within a forced air system, the particles will attract to and settle out on walls and other surfaces. Settling out of airborne pathogens will reduce their airborne counts (and has been used extensively in animal husbandry for infection control see
What's important about "ionization", as it pertains to microbial control, is the production of non-thermal plasmas. Below are some suggested readings. You may need to go to a University research library to find these. If you have trouble, let me know and I can send you hard copies. (drender@strionair.com)
M. Laroussi "Mechanisms of Inactivation of Bacteria by Air Plasma" Proceedings of the Colloquium on Plasma Processes 2003
M. Laroussi "biological decontamination by nonthermal plasmas" IEEE Transactions on Plasma Science V28, No1, Feb 2000
M. Laroussi "Nonthermal decontamination of biological media by atmospheric pressure plasmsa: review analysis and prospects" IEEE Trans on Plasma Sc V30,No4 Aug 2002
J Birmingham "bacterial decontamination using ambient pressure nonthermal discharges" IEE Trans on Plsma Sc V28, No1 Feb 2000
R Hackam "Air pollution Control by Electrical Discharge" IEEE Trans on Dielectrics and Electrical Inuslation, V7, No5, Oct 2000
K Urashima "Removal of VOC from air streams and industrial flue gases by nonthermal plasma technology" IEEE Trans Dielect and Electr Ins V7, No5, Oct 2000
Here are 3 vendors of commercial, in-duct-forced-air ionization technologies: