Science reviewed by: Dr Tiancun Xiao, inventor of DNO, Department of Chemistry, University of Oxford
Page reviewed by: Dr Chunli Cao, CEO, Healthy Air Technology Ltd
Published:
Short answer
Healthy Air Technology’s D-Orbital Nano Oxide (DNO) catalyst is not photocatalytic oxidation (PCO). PCO needs a UV lamp to activate its catalyst; DNO works at room temperature with no UV lamp or plasma. DNO breaks formaldehyde down into carbon dioxide and water.
In laboratory tests, the HA800 removed formaldehyde at a clean air delivery rate of 437.6 m³/h. Ozone at its outlet was below the test rig’s detection limit (under 0.003 mg/m³), even in Turbo mode with the ioniser on.
Why people ask
The US Environmental Protection Agency’s guide to home air cleaners says PCO cleaners use “a UV lamp along with a substance, called a catalyst”, that “currently available catalysts are ineffective in destroying gaseous pollutants from indoor air”, and that some PCO cleaners “produce new indoor pollutants”. That is a fair warning about UV-activated PCO. The rest of this page sets out how DNO is different and what has been measured.
How DNO works
- Air first passes through a HEPA-13 filter, which captures fine particles.
- It then passes over the DNO catalyst media. Gas molecules such as formaldehyde attach to the nano-oxide surface.
- At the surface they react with oxygen from the air and are oxidised. Formaldehyde ends up as carbon dioxide and water. Nitrogen oxides (NOx) and sulphur oxides (SOx) are handled differently: DNO converts them into stable salts that stay on the catalyst surface rather than returning to the air.
- For gases such as formaldehyde, the catalyst is not used up by the reaction, so the surface stays free for the next molecules. Activated carbon, by contrast, holds pollutants until it is full and may release them again.
The name refers to the d-orbital electrons of the transition-metal oxides that make the catalyst active. The technology was invented by Dr Tiancun Xiao of the University of Oxford’s Department of Chemistry and is protected by Chinese patents ZL201410737571.3, ZL201510446706.5, ZL201611265831.7 and ZL201910062327.4 (see Technology).
How DNO compares
| Technology | How it treats gases | Needs UV lamp or high voltage? | Main concern raised |
|---|---|---|---|
| DNO catalyst (HATL) | Oxidises selected gases at the catalyst surface; converts NOx and SOx into stable salts held on the media | No | Results are specific to the pollutants and models tested |
| Photocatalytic oxidation (PCO) | UV light activates a catalyst, usually titanium dioxide | UV lamp | EPA: can produce new indoor pollutants; limited gas removal |
| Plasma and stand-alone ionisers | Charged particles and reactive species in the air | High voltage | Can produce ozone with nothing to break it down; charged particles may settle on walls |
| UV-C lamps | Aimed at microorganisms, not gases | UV lamp | Some lamps produce ozone |
| Activated carbon | Adsorbs gases until full | No | EPA: short useful life; may release trapped pollutants when full |
What has been measured
| Model | Pollutant | Result | Conditions |
|---|---|---|---|
| HA800 | Formaldehyde | CADR 437.6 m³/h | Laboratory chamber |
| HA800 | Nitrogen dioxide | 99.11% reduction in 60 minutes | Laboratory chamber |
| HA800 | Sulphur dioxide | 93.3% reduction in 60 minutes | Laboratory chamber |
| HA500 | TVOC | 99.3% reduction in 60 minutes | Laboratory chamber |
| HA800 | Ozone emitted | Below detection limit (under 0.003 mg/m³) | 5 cm from outlet, Turbo, ioniser on |
| CETEC office assessment | TVOC in a meeting room | 232 to 95 µg/m³ (59%) | Real room; sampling period not reported |
Full details, including laboratories and test conditions where published, are on the Evidence & Test Results page. Further technical reports are available on request through our contact page.
Ozone and byproducts
Ozone. The HA800’s outlet ozone was below the test rig’s detection limit, under 0.003 mg/m³ (about 1.5 parts per billion). This was measured at its harshest setting: Turbo, with the ioniser on, 5 cm from the outlet. Ozone assessments for the HA500 and HA30 are available on request.
Formaldehyde. DNO breaks formaldehyde down into carbon dioxide and water rather than storing it.
The ioniser (negative-ion) function
Every Healthy Air Technology purifier includes a negative ioniser. It is part of the system design and works with the HEPA-13 filter and the DNO catalyst:
- Better particle capture. Negative ions charge very fine particles so they clump together into larger ones, which the HEPA-13 filter captures more easily.
- Ozone control. Ionisers can create small amounts of ozone. The DNO catalyst breaks ozone down into oxygen. That is why the HA800’s outlet ozone stayed below the detection limit in Turbo mode with the ioniser on.
- Fresher-feeling air. Many users find the air feels fresher with the ioniser on.
The ioniser can be switched off. The UK Department for Education’s guidance on air cleaning units (February 2026) does not recommend air ionisers, and NHS England’s HEPA bulletin (NETB 2023/01A) does not recommend ionisation without clear evidence. Buyers following that guidance can run the purifier with the ioniser off; the HEPA-13 filter and DNO catalyst keep working. Performance figures with the ioniser off are available on request.
What DNO does not claim
- It does not replace ventilation, source control or cleaning.
- It does not remove every gas; results apply to the pollutants and models tested.
- Laboratory chamber results do not guarantee the same result in every room.
- Purifiers support indoor air quality; they are not proven to prevent infection.
Frequently asked questions
Is DNO the same as PCO?
No. PCO needs a UV lamp to activate its catalyst. DNO works without UV light or plasma, at room temperature.
Does a DNO purifier produce ozone?
In testing, the HA800’s outlet ozone was below the detection limit (under 0.003 mg/m³), even in Turbo with the ioniser on.
What does DNO turn formaldehyde into?
Carbon dioxide and water.
What happens to nitrogen dioxide and sulphur dioxide?
DNO converts them into stable salts that are held on the catalyst surface, so they do not return to the air.
Can I switch the ioniser off?
Yes. Every model has a negative ioniser that can be switched on or off. It helps the HEPA filter capture fine particles, and the DNO catalyst breaks down the small amount of ozone ionisers can create.
Do I still need ventilation?
Yes. Air purifiers work alongside ventilation and source control, not instead of them.