Air ionizers can have some benefit at removing particles from the air near the unit, but unless the ionizer is paired with a fan and filter combination, it is not very effective at cleaning the air in a room. In addition, some ionizers produce ozone, which can be hazardous.
An ionizer works by generating charged particles that attract dust and other particulates in the air. As these particles bind together into larger clumps, they fall out of the air and are electrically attracted to surfaces in a room. While this can remove them from the airstream, unless they are vaccumed away, any agitation can break the electrostatic bonds and return them to the air. In addition, an ionic purifier without a fan to draw in air can only clean the air that passes naturally through the unit, reducing its effectiveness.
Ionizers also often produce ozone as a byproduct. While ozone generators can be beneficial for disinfecting a room, they are typically used in industrial settings due to the high concentrations of the gas and long cleaning times required. Ozone can actually cause respiratory problems, especially in people with pre-existing conditions, such as asthma or bronchitis.
The best air purifiers incorporate a fan and filter system to draw room air into the unit and capture particles. HEPA filters are designed to trap 99.97 percent of all particles .3 microns in size or larger. An ionizer can help these filters work more efficiently by attracting particles to the filter media, increasing the device's air cleaning power.