How an Ionizing (Electrostatic) Air Purifier Works

Air purifier tower with ionizer in living space

The Spruce / Danielle Moore

Air purifiers come in many designs, and some have the rather mysterious words "ionizer" or "ionizing" on their labels. These are also known as electrostatic air purifiers. There is considerable debate on the effectiveness of ionization when it comes to purifying air and even some question regarding the health effects of such appliances. Buying an air purifier is made more complicated by the ways in which ionization is used in different models.

Some appliances are pure ionizers, for example, that ionize the air but don't have any type of filter that actually removes particles from the air. Others are appliances that have standard air filters and also include an ionizing capacity. Finally, there are some very sophisticated air purifiers that include an ionizing option as well as top-end HEPA filters for capturing the smallest particles, along with UV lights that kill viruses and bacteria. These are generally considered the top-end units that offer the very best air purifying function.

air purifier ionizer illustration

The Spruce

How Ionization Works

Whether it is a pure ionizer or some form of air filter with an added ionization function, these devices all work by electrically charging air molecules with a negative charge. They then attract and bond with air pollutants such as cigarette smoke and pollen, which generally have a positive electrical charge. The manner in which these purifiers accomplish the ionization varies, depending on the design of the device.

Some non-filtering air purifiers work by means of a pair of electrically charged plates, through which air is drawn by a fan. One plate has a high negative voltage charge, and as pollutant particles pass by, they pick up a negative charge. Because opposites attract, these particles then cling to the other plate, which is charged with positive electrical current. As the room air moves through the purifier, it is gradually cleansed of all pollutants. The collection plates can be periodically washed and reused as they become laden with contaminates. If the plates become too dirty, though, the particles are simply sent back out into the room.

Other simple ionizers work by giving circulating air molecules a negative charge, then sending them back out into the room, where they eventually bond with positively charged pollutant particles, which gradually clump together with other pollutants. Eventually, the negatively charged clumps cling to positively charged surfaces, such as walls, furniture, and floors. One side effect is that this type of ionizer tends to create dust that settles on surfaces.

Ionization alone can be good at eliminating odors, which are generally caused by rather large air particles, but they are not very good at eliminating the very small particles that cause the most problems for allergy and COPD sufferers.

Other more sophisticated air purifiers that work by filtering air through different types of paper or fiber filters may also include ionization as one of their features, sometimes as an optional feature you can activate. Some of these appliances are quite sophisticated with multistage filtering that includes a HEPA filter, activated charcoal for removing odors, UV lights for sterilizing bacteria and viruses, and an electrostatic (ionizing) plate that causes particles to cling.

Can Ionization Be Hazardous?

There is some evidence of problems using ionization as an air-purifying technique. First, simple ionization does not really make small pollutant particles heavy enough to remove them from the air. They do not, for example, have any effect on viruses and other very small particles, unless the appliance is also equipped with a top-end HEPA filter and UV lights. Some people with allergies or COPD find that these devices actually increase their symptoms.

Second, and more important, ionizers can create ozone, which in itself is a dangerous pollutant. Small amounts of ozone are created when an electrical discharge (spark) splits oxygen molecules into elemental oxygen. Government environmental standards allow a very small amount of ozone to be created by these appliances, but critics point out that no amount of ozone can really be considered safe. And Consumer Reports and other testing agencies have found that low-quality ionizers and ionizing air purifiers can produce dangerous amounts of ozone when run constantly. Even a small amount of ozone can cause problems for asthma or COPD sufferers.

Instead, some experts argue that a purifier with a HEPA filter is a safer and more effective way to purify air.

Do Negative Ions Promote Wellness?

Some holistic health advocates argue that an ionizer air purifier freshens the air in a healthy way. They point to the fact that negative ions are present in the natural environment wherever the air is stirred up, especially around waterfalls, ocean surf, rivers, or mountains as well as after a rainstorm. The energizing effect you feel in the presence of turbulent water can be duplicated, they say, by the use of an ionizing air purifier.

Advocates believe that an environment in which negative ions exceed positive ions inherently promotes wellness and enhanced consciousness. Though unproven by mainstream science, this belief is a mainstay of holistic wellness strategies. Even if the effect is placebo in nature, it can be quite real for people who experience a sense of well-being through using an ionizing air purifier.

Tips for Buying and Using a Ionizing Air Purifier

If you are considering an air purifier, here are some things to know about the ionizing function:

  • Buy a purifier that also filters. Purifiers that only ionize are not regarded as very effective, and they may even create health hazards. Instead, buy a unit that has some form of filter that actually traps pollutant particles.
  • Choose a purifier with an optional ionizing function. If ionization is a feature you think you want, buy a unit where this function can be turned off and on as you wish. This will allow you to test the effectiveness of ionization and turn it off when it isn't wanted.
  • HEPA filters are best. These filters can trap particles up to .01 microns in size, which is sufficient to trap bacteria and most viruses. Be aware, though, that pathogens are not killed unless the purifier also has UV lights. If your HEPA filter requires cleaning or is close to the end of its lifespan, particles may not be filtered but instead returned to the room. If your home has more than the average amount of allergens, such as animal dander or smoke, the usual lifecycle of a HEPA filter can be greatly reduced.
  • Replace filters monthly if you have pets. A considerable amount of pet dander is put into the air, even by a single pet. Especially if you have two or more pets, changing the filter monthly—or even more often—is essential.
  • Choose purifier with UV light. If protecting against bacteria and viruses is essential, you'll want this option. Pathogens such as coronaviruses are generally not killed by standard air purifiers. While HEPA filters may capture such pathogens, they will not be killed unless the appliance also is equipped with UV sterilizing light.

The Best Ionizing Air Purifiers

Be aware that many "best" lists of air purifiers do not include ionizing purifiers among their top recommendations. In fact, many tout the missing function by marketing the product as "non-ozone-producing."

Of the well-regarded purifiers that do have ionizing functions, these four are among the best:

NuWave OxyPure Smart Air Purifier: The ionization feature is downplayed in this model, but the five-stage filter includes an "electrostatic precipitator" layer that is designed to capture particles through ionization. This is a very sophisticated appliance that also includes a filter layer to remove the ozone created by the ionizer.

PURO²XYGEN P500: This is a six-stage purifying filter that includes a HEPA filter, a negative ion generator, and a UV sterilization feature. It is a good unit for large rooms, up to 550 square feet.

Medify Air MA-40-W V2.0 Air Purifier: This model has a multistage filter system with a top-quality H13 HEPA filter that will capture bacteria and pathogens. The ionizing feature is an optional function.

Winix 5500-2 Air Purifier: This sophisticated purifier includes multistage HEPA filtering and a method of ionization the manufacturer calls "plasma-wave technology." The maker claims this is a superior method of ionization, since it uses a permanent filter and doesn't allow captured particles to circulate in the room and settle as dust.