Ozone is a harmful air pollutant and respiratory irritant that is mainly formed from outdoor pollution emissions (e.g., “smog”), though it may be found indoors or emitted by items in the home. Some air purifiers emit ozone as well, either as a by-product or intentionally. We recommend against using anything that introduces ozone into the air in your home (and so does the EPA).
If ozone levels are a concern for you in your home, you might wonder how it could be removed. Fortunately, there are a few air purifier technologies that can safely remove or filter ozone.
What is ozone?
Ozone is comprised of three oxygen atoms joined together (O3). Most oxygen in the atmosphere is formed from two oxygen molecules (O2). Ozone, on the other hand, is much more reactive than O2 because it readily combines with other substances it encounters, thus creating chemical reactions and forming new chemical compounds. This is why organic substances like latex can be damaged by ozone very quickly even at low concentrations, and why mucus membranes in your eyes, mouth, nose and lungs can also be damaged by ozone.
Ozone generally requires some amount of energy to be created out of O2. Electrical charges are a common source of this energy, which is why the distinctive smell of ozone, detectable even at low concentrations, is often associated with electricity. Lightning strikes create ozone, and smaller electrical charges do as well, including the charges generated by ionizing air purifiers. In the upper atmosphere, radiation from the sun forms ozone from oxygen. The ozone is then able to absorb some of that radiation, which would be harmful if it reached the surface of Earth.
Where does ozone come from?
According to the EPA, the primary source of ozone in the lower atmosphere is air pollution. Ozone is rarely emitted directly. Instead, car exhaust, power plants, chemical factories and other industrial facilities emit different forms of nitrous oxide and volatile organic compounds (VOCs). Sunlight provides sufficient energy to break these compounds down and reform them into new compounds, including ozone. This is why ozone levels in the lower atmosphere tend to be higher on sunny days with no wind.
In addition to industrial pollution, some household appliances also produce ozone. Laundry water treatment devices, fruit washes and facial steamers all produced ozone concentrations in excess of recommended levels, with even higher peak levels, according to the California Air Resources Board. Any device that uses ultraviolet light or frequent electrical discharge could also create elevated ozone levels. Certain office machines, such as printers and copiers, also generate potentially harmful ozone levels. Air purifiers that emit ozone obviously also create unsafe ozone levels.
What types of filters can remove ozone?
Because ozone is a gas rather than a particle, most common air purifiers will not remove it from the air. A HEPA filter or other type of mechanical filter will have no effect on ozone levels—this includes the filter that might be built into your HVAC system. Moreover, UV-C filters, ionizers, and ozone generators not only do not remove ozone, they actually produce it as a byproduct.
On the other hand, the characteristics of ozone that make it potentially harmful also make it possible to be filtered out of the air with another method: activated carbon. Ozone is reactive because the third oxygen atom attaches to other molecules very easily, with a tendency to “break off” of the ozone molecule, leaving only O2 behind. Activated carbon filters have numerous molecular spots for ozone molecules to attach to. A pilot study found that filters with carbon stages removed an estimated 60 to 70 percent of ozone from the air, compared to negligible removal by filters without activated carbon [Fisk et al, 2009]. Though more research is needed, these results seem promising.
Some proprietary products are designed specifically for ozone removal. Burnett Process filters use activated carbon, while Purafilter uses activated carbon and sodium permanganate to remove ozone and other chemicals from the air. They are typically installed in the HVAC systems in large facilities and public buildings.
Molekule’s PECO technology has been shown to reduce ozone levels, according to results from tests conducted with the University of Minnesota Particle Calibration Laboratory. A PECO air purifier assembly was run in a sealed test chamber and ozone was introduced to the chamber. After ten minutes, ozone levels dropped from 2.33 ppm (parts per million) to 1.66 ppm, then 0.08 ppm after 12 minutes. As a point of reference, the 1-hr California Ambient Air Quality Standard (CAAQS) for outdoor ozone is 0.09 ppm. In a second test, levels dropped from 30.2 ppm to 2.11 ppm after ten minutes, then to 0.08 ppm after 18 minutes.
PECO air purifiers use a photocatalytic reaction. During the photocatalytic reaction, ozone is decomposed and turned back into oxygen. Ozone goes from a very unstable molecule of three oxygen atoms, to a more stable molecule of oxygen due to the interaction of hydroxyl radicals that are produced in the PECO process.
It is also possible to remove ozone from the air without using a powered air purifier. Passive filtration, using building materials that can neutralize ozone, can reduce ozone levels over long periods of time. A 2012 study found that, “activated carbon mats and perlite-based ceiling tiles can provide substantial, long-lasting, ozone control.” [Cros et al, 2012].
Tips for preventing ozone in the home
How you deal with ozone in your home depends on the source of the ozone and whether it is coming from inside or outside the home. If you live in an area with high air pollution, there is not much you can do to control the external source of the ozone. Your best option might be to keep the windows closed, especially on warm and sunny days with little or no wind. Running an air purifier that can remove ozone in your home, either with a carbon filter or using PECO technology, may help lower ozone levels indoors.
If the source of the ozone is a device in your home, you have more options for removing it. For one, you could simply stop using whatever device is generating the ozone. But if you cannot avoid using a certain ozone producing device, try to use it only when no one is present in the room and allow 30 minutes after use before re-entering the room. Because it is so reactive, ozone eventually decays into regular oxygen even without using an air purifier. Finally, you should open the windows—fresh air from outside will quickly dilute the ozone in your house.
Ozone can be a significant problem, especially because it can damage the respiratory system. It is even more of an issue if someone in your home is sensitive to respiratory irritants due to emphysema, allergies or asthma. Unfortunately, industrial pollution causes most lower atmosphere ozone, so the only option is to find a way to remove it from your home.