Updated Winter 2022/2023
PCO Air Purifiers – Which Ones Reduce Mold and Which Ones are a Scam
Photocatalytic oxidation (PCO) is a technology that breaks down mold, VOCs as well as some pathogens.
My interest in these air purifiers comes from first-hand accounts of this benefiting homes with low levels of mold and volatile organic compounds (VOCs), and from the studies showing the eradication of mold and mycotoxins.
I am really excited about this technology as something that can safely break down mycotoxins and odors. Some people may be interested in its effects on breaking down viruses and bacteria as well (including SARS-2).
What is PCO?
In photocatalytic oxidation, UV light hits a catalyst, usually titanium dioxide, creating hydroxyl radicals (OH) and superoxide radical anions (O2–). These molecules bind with and break apart pollutants into harmless molecules.
Best for Mold, Not VOCs
Right from the first version of this article which I published in 2017, I qualified PCO technology as best for mold reduction, not for VOC reduction. I have a different post on the best air purifiers for VOCs.
The reason is that in real-life circumstances the chemical breakdown of VOCs is not a simple linear process. Byproducts like aldehydes can be (and often are) produced as an intermediary product of PCO.
With a high amount of hydroxyl radicals in a closed chamber experiment it will almost certainly break everything down (with enough time) into harmless molecules, but in a home with relatively high VOCs, the results could look different.
Brands Under Fire
It has not surprised me (or really concerned me) that big brands have come under fire for some of their claims. What did shock me when I did the initial research is that smaller air purifier companies get away with outrageously false claims since no regulatory body even has time to get to them.
I would say most companies are exaggerating claims. My focus was on the technology itself, and what studies based on that technology show us, and to remember that there are only a few types of air purifier technologies out there – their claims need to fall into one of a handful of categories.
What About HEPA?
HEPA filters do capture some mold spores and this article does include filters that include both PCO technology and HEPA, though the main focus of this article is on PCO.
If you’re looking at HEPA filters that don’t include PCO, and filters that help with high levels of VOCs, the post on filters for VOCs will be more relevant.
My recommendation is based on the most affordable and effective products that I have found. Upon purchase, I earn a small commission through affiliate links at no extra cost to you.
1. Vornado – The Best of Inexpensive PCO Air Purifier (What I’m Using)
They have true HEPA and activated carbon in addition to UV light and titanium dioxide. Most PCO units are much pricier or don’t include all three air purification methods.
True HEPA and activated carbon capture dust, pollen, pet dander, smoke, bacteria, mold spores, dust mites, and odors including VOCs.
PCO and carbon are the main technologies used to reduce odors and VOCs. (Ozone can as well, but it is very risky, I have a post all about ozone).
PCO actually breaks down molecules including molds and mycotoxins. I like that it has all three main air purification methods for a good price.
Why I chose this unit:
- The PCO component has true UV and titanium dioxide
- Respected brand name
- Noticeably brings down odors in new apartment and new cargo trailer
- Has a 10-year warranty
- Replacement parts are reasonably priced ($25 bulb every year, $35 titanium dioxide screen every 5 years – for the PCO related parts)
- Does not put out ozone
What I don’t like about it:
What I don’t like about it is that the unit itself offgasses a little bit (I am extremely sensitive). Not everyone thinks so or would notice this. After two weeks I found it to be good. I’m happy with it offgassing within two weeks. (Anyway, all air purifiers offgas a little).
The other drawback is that the amount of titanium dioxide is quite minimal so it may not be producing as many hydroxyl radicals as other PCO units. I am going to go with Molekule if I try another brand of PCO air purifier (more on them below).
Model 375 versus 575
The difference between the two sizes is that the PCO575 has a lower low speed and a higher high speed. The PCO575 has 2x the HEPA and 2x the activated carbon of the PCO375.
They both have the same PCO technology – so if you want to increase the effectiveness of the OH molecules in a large space you would want two of the PCO375 instead of one PCO575.
The 375 has a 113 CFM on high, 28 on low.
The 575 moves 156 CFM and is advertised for 258 sq ft., which would get you about 5 ACH in that room.
Some other PCO units are more or less the same unit re-branded: Continental Fan CX1000, Catalytic Pure Air, Field Control Trio / Sun Pure SP-20C. They seem to use a very similar PCO catalyst style to the Vornado with a titanium dioxide plated metal screen.
What are Air Exchanges Per Hour (ACH) – Air exchange per hour is how many times you are “replacing” the air in the room per hour, this is a key area of comparison with air purifiers.
ASHRAE (The American Society of Heating, Refrigerating and Air-Conditioning Engineers) recommends a minimum of 4 ACH for patient rooms in hospitals, 5 for intensive care units, and 25 for operating rooms. For the purposes of those extremely sensitive to mold and VOCs, we want about 5-10 air exchanges per hour.
To maximize how much air in the room the air purifier can process, put it in a central location.
How do You Calculate the ACH From a Unit’s Specs – You always want to find the CFM of the unit. The CFM is the capacity of the unit to move air – how much air it moves through the machine. CFM stands for Cubic Feet Per Minute. You need the CFM to calculate ACH. I made two calculators to calculate ACH from CFM and CFM needed from the room size and desired ACH.
2. Molekule – Top Overall Pick
If I had to go back and pick one right now, I would choose Molekule.
This is a slightly different technology called PECO.
Here is a summary of their studies – very promising results on eradicating mold. The data they showed me showed it worked better on mold than PCO.
This company has well-respected big names behind the design. The inventor of Molekule is the person who discovered PCO. He has an impressive resume.
Their newest filter option also contains HEPA and some carbon.
I will be trying this machine out as I think it is very promising, I like that this maximizes PCO (presumedly more OH molecules are produced compared to Vornado), plus it has HEPA now.
The warranty started as a 1-year warranty but now it is a 2-year limited warranty. The company has been around since 2016.
The Pro is the biggest model, it’s is advertised as cleaning up to 1000 sq ft. You will get 1 ACH in a room of 1000 sq ft with 8.5 ft ceilings.
The base model Molekule Pro does come with a basic particulate filter but that is likely to keep the other filters and components free of dust. If you want to add more particulate filtration they do now offer a HEPA filter for the Pro. (This is what I would go for, I want maximum PCO function but with HEPA as well).
The replacement filters for the Pro are $150 which lasts about 6 months, so replacement filter costs are high.
The new Molekule Mini provides 1 air exchange per hour in 250 sq feet. They offer a HEPA filter option for the Mini as well.
It sells for under $450 (often much lower, check the price here).
Which Size Should You Choose?
In a room that is 15 by 15, the biggest model would get you 4 ACH. That is a good number of air exchanges to aim for if you want a high level of air purification.
Here is my calculator that helps you size an air purifier for your room based on how many times you want to overturn the air in an hour.
If you can afford it, and if design is important to you, Molekule with HEPA is my top pick.
3. Puraclenz – Affordable Alternative
Puraclenz is a relatively new brand of PCO air purifier. At first glance it appears to be an affordable alternative to the pricier Molekule.
Remember that all PCO air purifiers are limited by the fact that OH molecules only last a few seconds so they can clean some air and surfaces close to the device but mostly they all clean air that passes through the device.
Also, a PCO device can create aldehydes whenever you are breaking down formaldehyde and other VOCs since they break down into smaller aldehydes. This is why I would not choose any brand of PCO air purifier for a home with high offgassing personally.
Puraclenz comes in three different sizes, small, medium and large. They suggest the small is for rooms up to 750 sq ft, medium for 1500 sq ft, and large for 3000 sq ft. However, there is no fan in the units, they do not have a CFM (cubic feet per minute) rating. In other words they don’t move any air through the unit. This was very surprising to me.
It’s great that they are ozone free.
1. Air Oasis – A Review
The Air Oasis Ionic Air
The Ionic Air has three components, one, a PCO component – germicidal UV light and a catalyst that is made of different metals to produce hydroxyl radicals; two, a bi-polar ionizer; and three it produces ozone (either through the UV light or via the ionizer).
The 3000G3 model is rated for 3,000 sq ft and only moves 11 CFM of air. 3,000 sq ft at 11 CFM is 0.02 air exchanges an hour. That is very little air movement. (I am using 8 ft ceilings in my calculations of CFM to ACH). But that’s not important for the ionizer and ozone components.
Technology – PCO
The company states that the PCO process creates “ionized hydroperoxides”. I have seen other PCO air purifier companies make this claim. This seems to me a confusing way to describe PCO which primarily produces hydroxyl radicals and secondarily produces superoxide radical anions (O2–).
Whenever I’m reviewing an air purifier I always keep in mind that there are only a small handful of possible technologies they can use. When it sounds like they have invented something new it means it’s time to look into their claims and see which of the few main technologies they are really using.
Technology – Biopolar Ionzation
A bipolar ionizer produces negative and positively charged ions that can cling to pollutants, dropping them to the ground where they can be cleaned and they might be able to break apart (chemically) some types of pollutants or biologicals. This type of ionizer can sometimes be advertised as cold plasma ionization (source).
Technology – Ozone
The air purifier also relies on low levels of ozone for air cleaning technology. You can have one made without the ozone production component but that seems to be a key component of its air cleaning abilities.
I personally do not consider any level of ozone, unless it is minuscule, to be safe to use in occupied spaces.
Final Thoughts on Air Oasis Ionic Air
I know this brand because mold doctors promote it. I was surprised when I dug into it to see how little air moves air through it, and that it gives off ozone. It was not approved by CARB at the time of writing the original version of this article (2017). It is now meeting California levels of safe ozone (CARB). (Though the upper limits of ozone in CARB are too high for me, personally).
Since the time I first wrote this article, it seems the company is much more clear that this is an ionizer. How much air it moves is not that central to an ionizer (but is for the PCO component). I’m a little wary of bipolar ionization which Dr. Marwa Zaatari, Mechanical Engineer, claims is not necessarily effective (in a now deleted essay, I’m guessing because she has been sued my a big air purification company).
It has a 3-year warranty and the replacement parts are $80 every 2 years.
Air Oasis iAdaptAir
The newer iAdaptAir is similar but claims to produce zero ppm of ozone. This is something I would be more likely to try.
It contains a HEPA filter, a carbon filter, PCO technology, and a bipolar ionizer.
Most ionizers give off ozone but it is possible to produce ions with minuscule ozone that does not register against background levels.
It comes in three different sizes for $399, $599, and $799.
This is really a great little unit if you want HEPA, carbon, PCO and you want (or don’t mind) the ionizer.
Air Oasis Versus Molekule – A Comparison
The main comparison that I can’t quantify is the strength of the PCO component – just how many hydroxyl radicals do they produce. Molekule has a good reputation for working well even before the HEPA option was added.
On the other hand, iAdaptAir has a really good value for what it provides. The only downside for me is I’m not a big fan of bipolar ionization as I have my doubts about its effectiveness and I tend to be sensitive to ionizers.
Both are good choices, however.
Here’s the comparison:
- Modified PCO technology
- HEPA filter is optional
- No ozone
- CFM ~80
- Costs $998
- Replacement filters $200 per year
- Modified PCO technology
- True HEPA filtration for particulates
- Some carbon for absorbtion of VOCs
- Bipolar ionizer
- No ozone
- CFM 151
- Costs $599
- Replacement filters $100 per year
2. Airocide Air Purifier Review
Another popular PCO machine that has been around for a while is Airocide. The APS 300 has a CFM of 40.
I like that the website has studies confirming that it doesn’t give off ozone. They used to have a short case study on breaking down mycotoxins when this article was first published in 2017 (though I can no longer locate it at the end of 2021).
It looks cool which is a plus.
The claims about removing dust, dust mites, and allergens do not seem all that accurate (especially after seeing what Molekule just went through with the FDA suit) since PCO machines do not filter particulate pollutants (according to the EPA).
It had a 5-year warranty when I first wrote this article, now it is a 2-year warranty. It costs $100 a year in replacement parts.
Why did I rule it out for myself: Most of the PCO machines do not include HEPA and activated carbon like the Vornado. This is a lot more expensive than Vornado or Molekule, but doesn’t move as much air.
FDA Approval of PCO Machines
The FDA approvals I have found are one for a PCO machine involving titanium dioxide (it proved to destroy some bacteria, viruses, and mold) for specific commercial uses.
The Airocide, Odorox, and Molekule Air Pro all have FDA approval as type 2 medical devices for use in hospitals. The first two use titanium dioxide and UV technology.
The FDA approval cannot be stretched to make safety or health claims on any device that deviates from this technology or has unknown additional technologies.
HiTech claims to be FDA approved, I can find no evidence of that. Anyone can search for FDA approvals here.
Adverse Reactions to PCO Hydroxyl Generators
I have heard of people having bad reactions to HiTech. I have heard only one bad reaction to Airocide, and a couple of bad reactions to AirOasis both the ozone and non-ozone types.
I do not know what accounts for these bad reactions. It does not appear that there is an ozone issue (apart from AirOasis). Dr. Daniel Cagua Koo has also noted that some patients simply don’t do well around this technology.
Since writing I have heard of some bad reactions to Molekule with about 50% of sensitive folks buying it being happy with it, and the other half not, and one bad reaction to Germ Guardian.
It is possible that PCO is creating harmful byproducts in high VOC buildings.
My interest here is for a house with extremely low VOC levels and already extremely low levels of mold. And the hope here is to keep the air as low in mold as possible.
I would love to hear from more people who have tried these other brands. Let me know if you have had good results or a bad reaction to a PCO machine.
Do PCO Machines Give off a Burning Smell
According to Airocide, the UV bulbs themselves emit a bit of a burning smell at first. They burn theirs in for two days, but sensitive people can smell it for up to a week.
The Vornado PCO had a very slight burnt smell at first which seemed like the smell of carbon.
Airocide made a statement that mold does not produce a smell when broken down by OH molecules.
HiTech states that the burning smell is mold/mycotoxins breaking down. I have found no evidence for this claim. A HiTech user also stated that the UV lights have burnt right through the “reactor pads”. This is consistent with a theory that the UVC lights are burning the “reactor pads” and causing a smell.
Corinne Segura is a Building Biologist Practitioner with 8 years of experience helping others create healthy homes.
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This post was written with the technical assistance of an electrical engineer, though the opinions and conclusions are my own.