Do Air Purifiers Produce Ozone?
Filter-only purifiers do not. Some ionizing and electronic types do, and ozone generators make it on purpose. Here is how to tell which kind you have and what the rules say.
Shaheer Ali Khan
Consumer Product Testing & Materials Performance Specialist
Last Updated
October 17, 2026
In This Guide
It depends entirely on the technology. Air purifiers that only use HEPA and activated carbon filters produce no ozone; ionizers, electrostatic precipitators, photocatalytic oxidation and plasma or bipolar ionization units can produce some; and ozone generators produce it deliberately, at levels the EPA warns can harm your lungs. California requires indoor air cleaners sold in the state to be certified by the California Air Resources Board, which limits ozone emissions to 0.050 parts per million, so a CARB-certified label is the quickest check. For most homes the simplest answer is to buy a filter-based purifier and switch off any ionizer feature it includes.
1. Which Kinds of Air Purifier Produce Ozone?
Ozone comes from electricity or ultraviolet light acting on oxygen. Any purifier that cleans air purely by pushing it through a filter has no mechanism to make it. Purifiers that use high voltage to charge particles, or certain UV lamps, can create some as a byproduct. Ozone generators are built to produce as much as possible.
| Technology | Produces Ozone? | Notes |
|---|---|---|
| True HEPA filter | No | Mechanical capture only |
| Activated carbon filter | No | Can remove some ozone from the air |
| Ionizer or negative ion generator | Can, usually small amounts | Varies by design; check certification |
| Electrostatic precipitator | Can | High-voltage plates; output varies by model |
| Photocatalytic oxidation (PCO) | Can | May also produce other byproducts |
| Plasma or bipolar ionization | Can | Limited independent data on byproducts |
| UV-C lamp | Depends on lamp | 185 nm lamps make ozone; ozone-free lamps block it |
| Ozone generator | Yes, by design | Not safe to run in occupied rooms |
The labels on the box do not always make this clear. A purifier described as HEPA may also have an ionizer switched on by default, and some marketing uses terms like activated oxygen, energized oxygen or pure air for what is actually ozone. The EPA has specifically called out that kind of language from ozone generator sellers.
Where you buy matters a little too. Indoor air cleaners sold in California have to be certified, but online marketplaces carry plenty of units with no certification at all, often with ionizer or negative ion features advertised as a selling point. Those are the units to be most careful with, because there is no independent check on what they emit.
So the practical question is not whether air purifiers produce ozone, but whether yours has a feature that can. Check the manual for an ionizer, plasma, PCO, electrostatic or UV feature, and look for CARB certification, covered below.
2. Do HEPA and Carbon Air Purifiers Produce Ozone?
No. A HEPA filter is a dense mat of fine fibers that catches particles as air passes through it. An activated carbon filter holds gas molecules on its surface. Neither involves high voltage or ultraviolet light, so neither creates ozone. The fan motor that moves the air does not produce a meaningful amount either.
Carbon actually works in the other direction. Activated carbon reacts with and removes some ozone from air that passes through it, which is one reason carbon filters are used where outdoor ozone is a concern. A HEPA plus carbon purifier will, if anything, slightly lower indoor ozone that drifts in from outdoors.
The catch is add-ons. Many purifiers sold as HEPA units include an ionizer, a plasma module or a UV lamp as an extra feature, sometimes switched on by default and sometimes with no separate switch at all. The ozone question is about those extras, not about the filter. If your purifier has one and lets you turn it off, turn it off, and the unit becomes a plain filter purifier.
This is why we favor filter-only designs for homes, particularly for people with asthma or allergies, who are the ones most likely to buy a purifier and the most likely to be bothered by ozone. A sealed true HEPA filter and a substantial carbon stage handle particles and odors without the trade-off. Our guide to whether a HEPA filter removes mold spores shows how much filtration alone can do.
3. How Much Ozone Do Ionizers and Electronic Purifiers Make?
It varies widely by design and model. Ionizers and electrostatic precipitators use high voltage to charge particles, and the electrical discharge involved can split oxygen molecules, some of which recombine as ozone. Well-designed units keep that to small amounts, and many are certified as meeting California's limit. Others, especially cheap units with no certification, may not.
Photocatalytic oxidation, or PCO, uses UV light and a catalyst to break down gases. Some designs produce ozone, and incomplete reactions can create other byproducts, including formaldehyde and other aldehydes, which the EPA lists as a potential drawback of the technology in its guidance on home air cleaners. Plasma and bipolar ionization devices make strong claims about killing germs and breaking down pollutants, but independent, peer-reviewed evidence for their real-world performance in homes is limited, and byproducts are a recognized concern.
There is a second issue with ionizers that has nothing to do with ozone. Charged particles tend to stick to the nearest surface, so instead of being captured in a filter they can end up on walls, curtains and furniture near the unit, sometimes leaving visible dark residue. The particles are out of the air for the moment, but not out of the room.
If you already own an ionizing or electronic purifier, check whether it is on the CARB certified list. If it is not, or you cannot tell, the safest approach is to switch the ionizing feature off if possible, or to replace the unit with a filter-based model. Our best air purifiers for mold rely on filtration rather than ionization for this reason.
4. Why Are Ozone Generators Different?
Because producing ozone is their whole purpose. An ozone generator does not filter anything. It deliberately creates ozone in the belief that it will react with odors, mold and bacteria. Some are marketed as air purifiers or air cleaners, which is where most of the confusion around this question comes from.
The EPA's position is clear. It states that ozone is a lung irritant, that available scientific evidence shows that at concentrations that do not exceed public health standards ozone has little potential to remove indoor air contaminants, and that ozone generators sold as air cleaners can produce levels that exceed those standards. Ozone can also react with chemicals already in indoor air to form other irritants, including formaldehyde and fine particles.
California went further. Its indoor air cleaner regulation prohibits the sale of ozone generators marketed as air purifiers in the state. Ozone generators are still sold elsewhere, and professionals sometimes use them for odor treatment in empty buildings, with people, pets and plants kept out and the space ventilated before anyone returns. That is a different use from running one in an occupied home.
For mold specifically, ozone is a poor bet. Levels safe to breathe do little to mold, and levels that affect it are harmful to people. Our look at whether ozone generators kill mold covers the evidence, and our guide on whether mold can grow in an air purifier explains how to keep a filter purifier from becoming part of the problem instead.
5. How Much Ozone Is Harmful?
Ozone is the same gas that forms smog outdoors, and the effects of breathing it are well documented. The EPA lists coughing, throat irritation, chest tightness or pain when taking a deep breath, shortness of breath, and worsening of asthma and other lung diseases. People with asthma, children, older adults and anyone active while breathing it are more sensitive.
Several agencies set limits, and they are useful reference points even though they apply in different settings. The table below shows the commonly cited figures. The point to notice is how small they are: fractions of a part per million, which a poorly designed device in a closed bedroom can approach.
| Limit | Level | Applies To |
|---|---|---|
| California indoor air cleaner limit (CARB) | 0.050 ppm | Ozone emissions from devices sold in California |
| FDA limit for medical devices | 0.05 ppm | Ozone from medical devices in occupied spaces |
| EPA outdoor air standard | 0.070 ppm, 8-hour average | Outdoor ambient air quality |
| OSHA workplace limit | 0.10 ppm, 8-hour average | Workers over a work shift |
These numbers are not targets to aim for indoors. The healthiest amount of extra ozone from a device in your home is none, which is exactly what a filter-only purifier adds. If anyone in the home has asthma or another lung condition, that is a strong reason to avoid ozone-producing devices altogether.
If you notice symptoms such as throat irritation, coughing or chest tightness that seem to appear when a purifier is running, switch it off, air out the room and talk to your doctor. Symptoms have many causes, and a doctor is the right person to sort them out.
6. What Does CARB Certification Actually Mean?
It means the device was tested and meets California's limits. Since 2010, the California Air Resources Board has required indoor air cleaning devices sold in the state to be certified, which includes electrical safety testing and, for devices that could emit ozone, a test showing ozone emissions no higher than 0.050 parts per million. The test is carried out under a standard laboratory method in a sealed chamber.
Because California is such a large market, many purifiers sold nationwide carry the certification, and CARB publishes a list of certified devices on its website, searchable by manufacturer and model. If a unit with an ionizer or other electronic feature is not on that list, that tells you something, especially if it is sold in other states without restriction.
Certification is a floor, not a guarantee of zero. A certified ionizing purifier may still emit a small amount of ozone under the limit. Some manufacturers go further and test to UL 2998, a separate validation for zero ozone emissions, which uses a much tighter threshold of 0.005 parts per million. Seeing that mark on a purifier with an electronic feature is reassuring.
Be skeptical of claims without either. Phrases like ozone-safe, low ozone or natural levels have no defined meaning. A model number you can find on the CARB list, or a UL 2998 validation, is the evidence worth looking for.
7. How Can You Check Your Purifier, and What Should You Buy?
Start with the manual or spec sheet. Look for the words ionizer, ion, plasma, PCO, photocatalytic, electrostatic, bipolar, UV or anything describing activated or energized oxygen. If none appear and the unit uses HEPA and carbon filters, it does not produce ozone. If one does appear, look up the model on CARB's certified list and check whether the feature can be switched off.
Your nose is a weak test. Ozone has a sharp, chlorine-like or after-a-thunderstorm smell, and some people notice it at very low levels, but sensitivity varies and the nose gets used to it quickly. Smelling it near a purifier is a reason to switch the feature off. Not smelling it does not prove it is absent. Inexpensive consumer ozone monitors also vary a lot in accuracy at the low levels that matter.
For a new purchase, the safest choice is simple: a true HEPA purifier with an activated carbon stage, a published CADR, and either no electronic features or ones you can switch off. That combination removes particles, mold spores, smoke and odors without adding anything to the air. Our guide on whether to run an air purifier 24/7 assumes exactly this kind of unit.
For mold-prone homes the case is even stronger, because people often buy a purifier there hoping it will treat the mold itself, and that is where ozone devices are most aggressively marketed. Filtration, moisture control and proper cleanup are what work. Our best air purifiers for mold are all filter-based, and our look at whether UV light kills mold covers the other common add-on.
8. Common Mistakes to Avoid
Assuming HEPA means no ozone
Many purifiers sold as HEPA units also have an ionizer, plasma module or UV lamp, sometimes on by default. The filter makes no ozone, but the add-on can. Read the manual, look for those features, and switch them off or check the model against the CARB certified list.
Running an ozone generator in an occupied room
Ozone generators are built to produce ozone, and the EPA warns they can exceed public health standards indoors while doing little for indoor pollutants. They are not air purifiers. If one is ever used, it is for unoccupied spaces, with people and pets out and thorough ventilation afterward.
Trusting your nose
Ozone has a sharp smell that some people notice at low levels, but sensitivity varies and the nose adapts within minutes. Smelling it is a reason to switch a feature off; not smelling it proves nothing. Rely on the technology type and certification, not on whether the room smells clean.
Falling for activated oxygen
Terms like activated oxygen, energized oxygen, trioxygen and pure air are used to sell ozone without naming it. If a purifier claims to add something to the air to clean it, find out what. A good purifier removes pollutants rather than adding a reactive gas to the room.
Ignoring the residue on the walls
Dark smudges on walls or curtains near an ionizer are particles it charged but did not capture. They left the air but stayed in the room. A filter-based purifier traps particles inside the machine instead, which is better for your walls and for the people sensitive to what is in that residue.
9. Frequently Asked Questions
Is ozone from an air purifier dangerous?
It can be, depending on the amount. Ozone irritates the lungs and can worsen asthma, and the EPA advises against devices that produce it to clean indoor air. A CARB-certified purifier stays under California's 0.050 ppm limit, and a filter-only purifier adds none. People with asthma or lung conditions should avoid ozone-producing devices and talk to their doctor about symptoms.
Do ionic air purifiers produce ozone?
Many do, in amounts that depend on the design. Ionizers use high voltage, which can create small amounts of ozone as a byproduct. Certified models meet California's limit, while uncertified ones may not. If you own one, look up the model on the CARB certified list and switch the ionizer off if your unit allows it.
Does a UV light in an air purifier produce ozone?
Only some lamps. UV lamps that emit at about 185 nanometers create ozone; lamps marketed as ozone-free use glass that blocks that wavelength and emit mainly at 254 nanometers, which does not. Check the manufacturer's specification or the CARB listing. A small UV lamp adds little cleaning power anyway, so a unit without one is a fine choice.
What is the difference between an air purifier and an ozone generator?
An air purifier removes pollutants, usually by trapping particles in a filter and gases in carbon. An ozone generator adds ozone to the air in the hope it will react with odors and microbes. The EPA warns that ozone generators can exceed health standards indoors and do little at safe levels. California prohibits selling them as air purifiers.
Are CARB-certified air purifiers ozone-free?
Not necessarily. CARB certification means ozone emissions tested at or below 0.050 parts per million, which can still be more than zero for ionizing or electronic units. A filter-only certified purifier emits none. For an electronic purifier with a stricter claim, look for UL 2998 validation, which covers zero ozone emissions at a much lower threshold.
Can an air purifier remove ozone?
Partly, if it has a substantial activated carbon filter. Carbon reacts with ozone and removes some from the air that passes through it, which can help on high-smog days when outdoor ozone leaks inside. HEPA alone does not remove ozone, because it is a gas. Keeping windows shut on high-ozone days also helps.
Should I worry about an older purifier I already own?
Check what it uses. A plain HEPA or carbon unit is fine. If it has an ionizer, electrostatic plates, plasma or a UV lamp, look up the model on CARB's certified list and turn those features off if you can. If it is an uncertified ionizer with no off switch, replacing it with a filter-based unit is the cautious choice.
Related Air Purifier Safety Guides
Buyer's Guide
Best Air Purifiers for Mold
Filter-based true HEPA and carbon units, with no ozone-producing add-ons needed.
Straight Answer
Should You Run an Air Purifier 24/7?
Why continuous running wins, and why to switch off any ionizer first.
Mold
Do Ozone Generators Kill Mold?
What it takes for ozone to affect mold, and why those levels are unsafe for people.
The Bottom Line
Whether an air purifier produces ozone comes down to how it cleans. Filters make none: true HEPA and activated carbon trap pollutants without adding anything to the air. Ionizers, electrostatic, PCO and plasma units can produce some, and ozone generators produce it on purpose, at levels the EPA says can harm your lungs while doing little to clean the air.
Check the features, look for CARB certification on anything electronic, switch off ionizers you do not need, and never run an ozone generator in a room people use. For most homes, a sealed true HEPA purifier with a real carbon stage is the right answer, and it is the safest one too.
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About the Author
Shaheer Ali Khan, Consumer Product Testing & Materials Performance Specialist
Shaheer Ali Khan holds a PhD in Materials Science and Engineering from Georgia Tech and is an ASQ Certified Quality Engineer and Certified Reliability Engineer. He leads testing for household appliances, vacuums, cleaning products, and caulks, adhesives and sealants.