An ionizer is a type of air filter that uses high voltage to charge molecules in the air, to help clean them. Since they are using electricity, rather than a passive form of filtration, they do not require filters that need to be regularly changed. As a result, they are very convenient for a number of different uses, most especially in the house or in the car, and there are a wide range available on the market. Depending on a number of factors, an air ionizer can cost anywhere from around $50 US Dollars (USD) to many hundreds of US Dollars.
The general premise behind an air ionizer is that the charged electrode attracts particles, in the same way a statically charged bit of fabric might pull dust or dander from the air. These charged particles may then clump together and fall out of the air to the ground, or they may be attracted to a large surface, such as a wall, or they may be drawn to an attached dirt trap, which can then be easily brushed off to be cleaned.
An air ionizer should not be confused with an ozone generator, although the way both devices function is quite similar. An ozone generator is built to draw in extra oxygen ions, which then bond with an O2 molecule to create ozone. Although an air ionizer will generally create some small amount of ozone, this is not its intent, and the two devices have quite different effects.
In recent years, especially in East Asia, and particularly in Japan, the ionizer has begun to crop up in any number of small devices. Rather than being used as a stand-alone device, it instead is added to things like computers, toothbrushes, air conditioners, and refrigerators. This eliminates the need to buy a stand-alone ionizer, as every appliance can potentially have one always operating, drawing particles out of the air.
When looking to buy an ionizer, it is important to make sure it does actually generate negative ions. In some cases cheap ionizers, especially those coming from Asia, may not actually ionize the air, simply using the term as part of a normal air filter. Also check to make sure the device comes with a warranty, as they are prone to problems, and can be quite costly to repair. Generally speaking, it is worth the investment of a bit more money to get an ionizer that will function well and last for a while.
The most important feature of an ionizer is its power consumption. More powerful ionizers, which generate more negative ions, will draw a great deal more electricity. Depending on how much contamination tends to be in the air, you may want to get a model that draws less power, thereby saving your energy consumption. On the other hand, if you feel you need a great deal of cleaning regularly, getting the most robust model available may make more sense. Also look at the size of the device, as having a highly portable model can be a great way to save on buying multiple ionizers, as you can simply move it from room to room.