Upated Winter 2022
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, is that in real-life circumstances the chemical breakdown of VOCs is not a simple linear process. Byproducts like formaldehyde can be produced as an intermediary product.
With a high amount of hydroxyl radicals in a closed chamber 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.
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.
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. I am going to go with Molekule if I try another brand (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.
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.
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.
2. GermGuardian – The Best Small & Inexpensive Unit
Another brand that is very affordable and also incorporates HEPA, carbon, and PCO is GermGaurdian.
I have heard of people using it in trailers and being happy with it. At $89 it’s a steal. And it has 5.5 ACH in 171 sq ft.
But this is small and simple, I would only use it in tiny spaces if you can’t afford something better.
Buy the GermGuardian on Amazon.
3. 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.
Their newest filter option also contains HEPA and some carbon.
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.
I will be trying this machine out as I think it is very promising.
The warranty started as a 1-year warranty but now it is a 2-year limited warranty. The company has been around since 2016.
Molekule Air Pro
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.
It goes for $1,199.
The Molekule Pro does have a basic particulate filter but that is not the primary function of this unit. That is likely to keep the other filters and components free of dust.
The replacement filters for the Pro are $150 which lasts about 6 months, so replacement filter costs are high.
This is their original model. They state it cleans up to 600 sq ft. You get 1 ACH in a room of 600 sq ft with 8.5 ft ceilings.
It goes for $998.
The replacement filters are about $200 per year.
The new Molekule Mini provides 1 air exchange per hour in 250 sq feet.
It sells for $499.
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, if design is important to you, and if you only need PCO technology (not HEPA or carbon) Molekule is my top pick.
1. Air Oasis – A Review
The Air Oasis Ionic Air
The Ionic Air has three components, 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 if you are using this as an ionizer.
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 in 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 ineffective it would be at moving 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 CARB are too high for me.
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. However with hydroxyl radicals, the molecules do not travel very far, and so air passing through is important so that contaminants interact with the ions before they dissipate.
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 without adding any other technology.
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
- No other technology added
- 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.
3. What I Would Not Go With….
This is an air purifier that I myself would not consider. You can skip this section unless you want to hear all the details about HiTech.
HiTech Air Solutions Review – Is it a Scam?
HiTech Air Solutions, a brand known among some extreme mold avoiders, makes Air Reactors that claim to be PCO machines. And wow, what I found out was very disturbing to me.
To start, the 101 model ($2000) is very expensive relative to the other PCO machines. From looking at the inside of the machine they use basic components that total under $150 for all visible parts if I bought them: four foam/coarse dust filters, two UVC lights, two computer fans, and a 4U 19″ rack case.
The claim here is that some of these filters are photocatalysts that produce OH molecules – that there is something invisible called “Technosite®” (no evidence of this trademark with USPTO) impregnated onto the filters.
They may be using something similar to PALCCOAT (confirmed not partnering with this brand) which is a clear titanium dioxide catalyst (FYI $13 per square meter). I have found no evidence of a patent held by HiTech or Ray Robison, owner, on anything in the machine.
I have also seen two other odd claims from sales reps of the company – one, that the filters are coated with Sporax (I have seen pictures of their filters with Sporax, though they later denied this.) And that both the filters and the bulbs are also coated with something proprietary – both things that I would want to know are safe to use with UVC light.
HiTech makes some pretty astonishing claims that not only have not been backed up by evidence, but feel free to ask a chemist about how this is even possible:
They claim their OH molecules (which are produced by the PCO process) last much longer in the air than the other air purifiers’ OH molecules (~6 weeks instead of ~15 seconds) based on “a study by Texas Tech”, though this study cannot be produced by the company. Dozens of phone calls were made to track down the existence of this study and nothing turned up. Even more, the University claims it does not conduct studies give the results on the phone, and then withhold the report for large sums of money (as the reps claim).
I have not found any evidence that this “study” exists or ever existed, or that this produces a totally different kind of OH molecule. Just ask a chemist how you can have a stable but also reactive OH molecule.
I would like the company to disclose what they are using in this machine so we can know if it is safe and effective, or, provide real studies that show which molecules and byproducts this machine produces.
The burning smell is worrisome to me. I have seen photos of users’ machines showing the filters having been burned through by the UV light. That will produce offgassing. The accounts I have seen of bad reactions are also worrisome.
HiTech claims it produces 99.9% pure air. I have seen no studies to back up this very broad claim. What is the level of contamination in the air to start, and what is “pure air”? Also note, PCO technology does not filter particulate pollutants (EPA).
I have contacted a technical rep, sales rep, and the owner for these studies – they responded but were not able to provide them. Others have contacted them as well for this information.
Their bigger units are ~$5000 and ~$6000 dollars!
The HiTech sales reps make 25% commission off each unit and they usually recommend multiple units for houses. The commission for the three sizes is roughly: $500, $1000, and $1500! The cost of the replacement parts are $140, $190, and $295 per year, for the three different sized units.
HiTech has not submitted their Air Reactors to CARB at the time of writing in 2017, to confirm they give off a safe level of ozone. However, the bulbs they are using are USHIO brand UV bulbs with a 2G11 / PL-L base which do not give off ozone. They use another brand as well, LSE Lighting UV bulbs, with the same base. From what I can tell this bulb would not be any different from the USHIO brand.
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.
If you are in high VOCs I would focus on a filter that has a lot of carbon – like these I review here.
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.
HiTech reps speculate to buyers that the bad reactions may be helpful (some kind of detox or “herx”), which is ethically unsound in my opinion. With no data to suggest this is detox, we should take a precautionary approach.
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.
HiTech states that the burning smell is mold/mycotoxins breaking down. I see no evidence for this claim.
Airocide made a statement that mold does not produce a smell when broken down by OH molecules.
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.