Let me start off by clarifying that there is a big difference between an "Air Ionizer" and an "Ozone Purifier." They are not the same. However it's easy to get confused because:
"Several name brand ionizers have been found to generate dangerous ozone levels as a byproduct of their ionization methods."
After we clarify these technologies and what each can do we'll review the popular Ionizers and Ozone purifiers on the market. By the end you should be able to determine if they fit the type of air purifier right for your needs. Ionizers and ozone machines are also different in what they help when it comes to air problems. Here's the difference:
Air Ionizers - Both positive and negative ions are naturally occurring in nature, and essential to life itself. An air ionizer purifier simply creates more of them. Many air pollutants (cigarette smoke, soot, carbon fumes, etc.) are made of highly charged (+ and -) particles. Inside an ionizer air purifier you'll often find highly charged flat plates (think "cookie pans"). These plates, charged with positive and negative ions, operate like a magnet - attracting pollution to the surface of the metal.
Ozone - Although Ozone is also naturally occurring ozone is something different than ionization. It is often created by lightning and sometimes you can smell it in the air after a lightning storm. Too much car pollution can also create ozone, and generate Ozone warnings. Oxygen is 02 (two molecules) while Ozone is a rare and very unstable "third molecule" added to an oxygen molecule (O3).
The grid style and the plate style are both usually washable and both do the same thing. (The picture below is from the Alive Air Purifier which uses an ionizer grid as 1 of it's 7 types of purification.)
Negative ions have been researched to assist in breathing problems and in improving brain function. That's why they have also been called: "Air Vitamins."
Companies like EcoQuest (now called Vollara, before Ecoquest called Alpine or Living Air) market Ozone machines for air purification. They've taken a lot of heat from the government (hence the name changes) because of the Ozone Problem.
Because of the air ionizer ozone purifier problem states like California have enacted strict ozone regulations and testing.