Ionic air purifiers are not filter systems. Ionic air purifiers work by sending out negatively charged ions into the air of your home. The ions latch onto chemicals and particles such as dust, tobacco smoke, and pollen, causing them to become attracted to each other and to the interior surfaces of your home. The result is that they drop right out of the air. You wipe, mop, and vacuum the precipitant as part of your regular chores. This may seem like a dirty way to purify the air, but many machines are highly effective at it.
Some ionic air purifiers have fans and others dont. Those with fans can be noisy or very quiet, depending on the brand. Those without fans rely on existing air currents caused by ceiling fans, human movement, and so on to carry the ions to the various nooks and crannies of the room. If you buy one with no fan, be sure to place the unit accordingly. If you buy one with a fan, wipe off the grille once in awhile, just as you would with a ceiling fan.
One variation on the ionic air purifier is the electrostatic air purifier. It works by actually drawing air in through a carbon or HEPA pre-filter, which catches larger particles such as dust and pet dander. Then, the smaller particles, such as aerosols, pass through an electrical field, which ionically charges the pollutants. Immediately the newly charged particles are caught upon magnetized plates. To maintain peak efficiency, you periodically wash the filter, the electronic cell, and the electrostatic collector plates. This could be anywhere from every week to every six months, depending on air quality.
Most ionic air purifiers produce some ozone as a byproduct of ionization. Ozone has a distinct, fresh smell that can help to reduce and mask certain odors. But ozone can be bad for your health when exposed in large amounts or for a long period of time. Be sure to buy a unit that emits 50 parts per billion or fewer.