Does Photoelectrochemical Oxidation (peco) Emit Ozone?

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Written By Jamila W.

Photoelectrochemical oxidation, known as PECO, is an emerging air purification technology that degrades a wide range of common indoor air pollutants. PECO is derived from an earlier technology called photocatalytic oxidation (PCO) which several studies have associated with the emission of ozone. If you’re considering purchasing a PECO air cleaner, ozone emissions are an understandable concern. In this article, we provide a clear answer to the question of whether PECO emits ozone.

No. PECO air cleaning technology does not emit ozone. This has been independently verified by the California Air Resources Board (CARB) which tested PECO air purifiers for ozone emissions in 2018 and certified that they are ozone-free

What is Photo Electrochemical Oxidation (PECO)?

Photo Electrochemical Oxidation (PECO) is a new air-cleaning technology that uses a UV-activated catalyst to degrade and destroy common indoor air pollutants. This emerging technology has shown excellent performance in eliminating organic particulates and gasses from room air, including 

  • Volatile organic compounds (VOCs)
  • Biological agents like viruses, mold, bacteria, and pollen
  • Cigarette smoke
  • Formaldehyde
  • Nitrogen dioxide
  • Ammonia
  • Particulate Matter including PM1, PM2.5, and PM10 particles

How PECO works

PECO air purifiers contain a special catalytic filter that is coated with a proprietary titanium dioxide-based nanocatalyst. In the presence of UV light and an electrical current, the activated catalyst generates high concentrations of hydroxyl free radicals from water vapor in the intake air. 

These free radicals are powerful oxidants that destroy organic particulates and gasses that come into contact with the catalyst surface. The destruction of pollutants is thorough, leaving harmless carbon dioxide and water in exhaust air.
PECO was developed from photocatalytic oxidation (PCO), which has a similar mechanism of action. But PCO’s oxidative activity can be variable, leading to the generation of harmful emissions including ozone. PECO improved the performance of PCO by introducing an electrical current that enhances the oxidative activity of the photocatalysts. This makes a PECO air cleaner much more efficient and even capable of degrading ozone rather than emitting it.

Why is ozone emission a concern?

Ozone (O3) is an inorganic gas composed of three oxygen atoms. that is naturally present in the Earth’s atmosphere. It is present in high concentrations in the stratosphere where it shields the Earth from excessive UV radiation. However, it can be generated at a terrestrial level where it can cause health and environmental harm. This type of ozone gas is called tropospheric ozone.

Health effects of ozone 

Ozone is a noxious gas and respiratory irritant. Exposure to ozone in indoor air causes the following symptoms:

  • Headaches
  • Eye and nose irritation
  • Respiratory tract irritation
  • Coughing
  • Shortness of breath
  • Chest pain
  • Fluid in the lungs. 
  • Development and aggravation of asthma

Tropospheric ozone exposure limits

Because of these health risks, state and federal agencies have enacted stringent exposure limits for ozone. The Environmental Protection Agency specifies an eight-hour exposure limit for ozone of 0.07 parts per million (ppm). 

Environmental effects of ozone

Tropospheric ozone can also harm trees, plants, and other vegetation. Ozone exposure reduces photosynthesis in plants, slows their growth, and makes them susceptible to disease.

Where does tropospheric ozone come from?

Ground-level ozone is a notable outdoor air pollutant. It is largely generated from the reaction between UV light and the pollutant gasses nitrogen dioxide, sulfur dioxide, and VOCs. This type of ozone is the smog that is prevalent in urban areas. 

Air Purifiers Can Be a Source of Ozone in Indoor Air

Air cleaning devices are a novel source of ozone emission in indoor spaces. The emission of ozone by the majority of air purifiers is unintentional, with the gas released as byproducts of the air purifier’s normal function. 

Ozone emissions have been detected in the following classes of air-cleaning devices:

  • PCO air cleaners 
  • Uncoated UVGI lamps
  • Plasma
  • Electronic air cleaners
  • Portable and duct-mounted Electrostatic precipitation (ESP) devices
  • Ionizers 
  • Ion generators

The Environmental Protection Agency advises that air cleaning devices marketed with the terms ‘plasma’ or ‘ions’ may be capable of generating high concentrations of ozone.

UV light in air purifiers can generate ozone

Specific frequencies of UV light used in air purification devices are increasingly recognized as a cause of ozone generation by air purifiers. Ozone is generated by UV light at specific wavelengths. In the presence of elevated concentrations of nitrogen dioxide and other gasses, the UV lights used by air purifiers may generate ozone.  

This usually takes place if the UV wavelength is suboptimal. At light wavelengths below 240 nm the bonds in oxygen (O2) can be disrupted, leading to the formation of ozone (O3). The worst UV wavelengths for this problem are between 100 and 200 nm.

Ozone generators are also being marketed as air purifiers

There is also a class of air-cleaning devices that intentionally emit ozone. Manufacturers who sell ozone generators as air purifiers cite the disinfecting effects of ozone. However, the Environmental Protection Agency has stated that there is no federal or state agency that has approved ozone generators for air purification because of their obvious health risks. 

In Conclusion

Ozone emissions from air purifiers are a valid concern. PECO air purifiers are an excellent choice for an air cleaner that has been independently tested and certified to be ozone-free.