Some air cleaners marketed as "purifiers" intentionally generate ozone, a lung irritant and the main component of ground-level smog. EPA is direct: "No agency of the federal government has approved these devices for use in occupied spaces." The agency's testing found that a large ozone generator operating at high setting in a 350-square-foot room quickly produced concentrations of 0.50-0.80 ppm — 5 to 10 times higher than public health limits (EPA).
What ozone does to your lungs
EPA documents that even relatively low amounts of ozone can cause chest pain, coughing, shortness of breath, and throat irritation. Higher exposures can decrease lung function, aggravate asthma, inflame lung tissue, and increase susceptibility to respiratory infection. Ozone may also worsen chronic respiratory diseases and compromise the body's ability to fight respiratory infections (EPA).
The California Air Resources Board (CARB) goes further, warning that elevated exposures can cause permanent lung damage and that repeated exposure can increase the risk of dying among people already in poor health. CARB also notes that ozone deadens the sense of smell — meaning users may not realize they are being exposed to dangerous levels (CARB).
| Standard or Limit | Ozone Level | Source |
|---|---|---|
| FDA medical device limit | 0.05 ppm | FDA |
| CARB certified air cleaner max emission | 0.050 ppm | California ARB |
| EPA NAAQS (outdoor, 8-hr avg) | 0.08 ppm | EPA |
| CARB outdoor 8-hr standard | 70 ppb (0.070 ppm) | California ARB |
| OSHA workplace limit (8-hr avg) | 0.10 ppm | OSHA |
| NIOSH ceiling limit | 0.10 ppm | NIOSH |
| Ozone generator output (EPA test) | 0.20-0.80 ppm | EPA testing |
| Levels needed to kill microbes | 50-100x outdoor standard | CARB |
The paradox: at safe levels, ozone doesn't clean
CARB's fact sheet states plainly: "Ozone, at safe levels, does not clean the air." The ozone concentrations needed to reduce odors and pollutants in unoccupied spaces are above levels generally thought to be safe for humans. To effectively kill microbes, ozone must reach levels 50 to 100 times the outdoor air quality standard — concentrations that would be extremely hazardous to anyone present. Independent studies by EPA, Consumers Union, and others found that ozone-generating devices do not effectively destroy microbes, do not remove odor sources, and do not reduce indoor pollutants enough to provide health benefits (CARB, EPA).
Ozone creates new pollutants.CARB warns that ozone can react with existing chemicals in indoor air to create additional toxic pollutants, including formaldehyde and ultrafine particles. So an "air purifier" that generates ozone may actually increase the concentration of harmful contaminants in your home — the opposite of its advertised purpose (CARB).
Which devices generate ozone?
Not all electronic air cleaners are equal. EPA and CARB distinguish three categories: ozone generators produce ozone directly and purposefully; ionizers and electrostatic precipitators produce ozone indirectly as a byproduct of their charging process. While ionizers and ESPs typically emit much less ozone than dedicated ozone generators, some can still produce enough to cause unhealthy exposures. CARB's 2008 regulation limits all indoor air cleaning devices to no more than 0.050 ppm ozone emissions, and more than 300 manufacturers have obtained CARB certification by meeting this standard (EPA, CARB).
What ASHRAE says
ASHRAE's Position Document on Filtration and Air Cleaning states that filtration and air-cleaning technologies are not recommended for use if they produce significant amounts of contaminants that are known or expected to be harmful for health. ASHRAE Standard 62.1, the recognized ventilation standard for acceptable indoor air quality, includes provisions for air-cleaning devices and references the FDA's 0.05 ppm ozone limit for medical devices. The standard's 2025 edition continues to address air cleaning as part of a comprehensive ventilation strategy (ASHRAE).
What the CPSC review found at low levels
A CPSC-commissioned review of ozone health effects literature found that while studies did not demonstrate significant group-level adverse health effects at or below 50 ppb (0.05 ppm), the evidence was insufficient to establish a safe threshold. Notably, bronchial epithelial cell cultures from asthmatic subjects showed significant inflammatory responses at ozone levels as low as 10 ppb — far below the FDA limit. The National Research Council's 90-day continuous exposure limit was set at 20 ppb, and a study of cross-country runners found performance deterioration beginning at approximately 30 ppb (CPSC).
Safe alternatives for indoor air cleaning
- HEPA filtration: Mechanical filters (MERV 13+) remove particles without producing ozone. See our MERV ratings guide.
- Carbon adsorption: Activated carbon filters remove gases and odors without ozone byproducts.
- UVGI systems: Properly designed UV-C coil irradiation controls biological growth on coils without introducing ozone into occupied spaces. See our UVGI guide.
- Source control: Eliminating pollutant sources (smoking, combustion, off-gassing materials) is more effective than any air cleaner.
- Ventilation: Diluting indoor pollutants with filtered outdoor air per ASHRAE 62.1 remains the primary strategy.
- CARB-certified devices: If using an electronic air cleaner, verify it is CARB-certified (max 0.050 ppm ozone emission).
Naming a product or manufacturer in this article is for identification purposes only and does not constitute an endorsement by HVAC Zone Inc. We are a multi-brand dealer and remain neutral on brand preference.
Concerned about indoor air quality in your home or building? Request a consultation — we assess your air cleaning needs and recommend ozone-free filtration strategies grounded in ASHRAE standards.