Ionisers, ozone generators and "plasma" purifiers
Devices that charge particles or make ozone can irritate the lungs and do less than a plain HEPA filter. What to avoid and what to switch off.
Ozone generators: avoid completely
Some devices are sold as “air purifiers” or “ozone purifiers” but deliberately produce ozone, claiming it “destroys pollutants” or “refreshes air”.
- Ozone is itself a lung irritant. It can cause coughing, chest tightness and shortness of breath, and worsen asthma. This is exactly what you’re trying to protect sensitive people from.
- At levels safe to breathe, ozone does little to remove pollutants. It does not remove PM2.5.
- Ozone can react with other chemicals indoors to form new irritants and fine particles.
US public-health agencies advise against using ozone generators in occupied spaces. California’s air regulator sets a strict ozone emission limit for air cleaners sold there, a useful benchmark when a product claims “certified low ozone”.
Ionisers, “anion”, “plasma” and “photocatalytic” modes
Many purifiers add a feature that charges particles or creates reactive molecules:
- Charged particles may stick to walls and furniture instead of being captured, then get stirred back up later.
- Some of these technologies can create ozone or other by-products.
- Independent evidence that they improve health is weak.
What to do: buy a purifier that relies on a mechanical HEPA filter, and switch off any ioniser or plasma mode. If a product can’t run without it, choose another one.
UV lights in purifiers
UV-C lamps are aimed at germs, not pollution, and do nothing for PM2.5. Some UV lamps produce ozone. A UV feature is not a reason to buy.
The simple test
Ask: does this device have a HEPA filter and a published particle CADR? If yes, it will reduce PM2.5. Everything else is optional at best.