PCO Air Purifier | Overview

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Written By Jamila W.

Photocatalytic oxidation, UVPCO, or PCO air purifier technology emerged in the 2000s and has become a powerful solution for removing pollutants from indoor air in a range of settings. It can degrade many of the common pollutants of indoor air making it an effective alternative to mechanical filter-based air cleaning. In this article, we explain:

  • What a PCO air purifier is
  • How a PCO air purifier works
  • The advantages and disadvantages of PCO air purifiers
  • How PCO air purifiers compare with other air-cleaning technologies

What is a PCO Air Purifier?

A PCO air purifier is an air-cleaning device that eliminates air pollutants from indoor air using a chemical process called photocatalytic oxidation. This technology combines ultraviolet light (UV-A or UV-C) with a titanium dioxide catalyst to generate oxidizing particles, called free radicals, from water vapor. These hydroxyl radicals break apart the molecular bonds in indoor air pollutants, eliminating them from your environment.

Rather than trapping pollutants, PCO breaks them down into carbon dioxide, water, and harmless mineral debris. This process continues as long as the titanium oxide catalyst is irradiated with UV light. Elimination of air pollutants using PCO rapidly produces a marked improvement in indoor air quality

Types of pollutants removed by PCO

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The oxidative action of PCO air cleaners targets organic (carbon-containing) pollutants. The hydroxyl free radicals, generated from water vapor, can break carbon-containing molecular bonds to generate carbon dioxide and water. This means that PCO is effective at removing organic particulate and gaseous pollutants, including

  • Volatile organic compounds (VOCs)
  • Acrylamide
  • Formaldehyde
  • Bacteria
  • Viruses
  • Molds
  • Pollen
  • Cigarette smoke
  • Particulates (PM1, PM2.5, and PM10)

PCO air purifier development

The photocatalytic oxidation technology that PCO air filters use was identified over a century ago by Dr. Alexander Eibner, a German chemist. He discovered that the illumination of zinc oxide produced a bleaching action. 

In the 1930s, titanium dioxide was identified as a photocatalyst by scientists Doodeve and Kitchener. Further research by Japanese scientists Akira Fujishima and Kenichi Honda in the 1970s found that TiO2 could catalyze the electrochemical photolysis of water. This discovery led to the development of a range of applications for the titanium dioxide photocatalyst. Aside from air purification, titanium dioxide was used in paper manufacturing, water treatment, and disinfection. 

By the 2000s, PCO emerged as a competent air purification technology. Increasing concern about indoor air pollution has led to its wider adoption as an effective way to eliminate allergens and pollutants in room air. Its ability to reduce levels of VOCs and other gaseous pollutants has increased demand for this type of air purifier.

How Does a PCO Air Purifier Work?

PCO air purifiers are powered devices that draw in room air to be cleaned. Within the device, there is a high-surface-area media coated in the titanium dioxide catalyst. Pollutants in the indoor air that enters the device are trapped or adsorbed to the surface of the catalyst.

In the presence of UV light, the catalyst is activated to generate hydroxyl free radicals that oxidize and break down adsorbed pollutants. If the chemical reaction is complete, the adsorbed organic pollutants are transformed into carbon dioxide and water that are released in exhaust air.

The efficiency of PCO is determined by several factors

PCO air purifiers have to manage three key variables to perform optimally and safely:

  1. The frequency of UV light used: The titanium dioxide photocatalyst needs to be irradiated with the correct frequency of UV light to perform optimally. Certain UV wavelengths can cause PCO devices to generate ozone.  
  2. The concentration of air pollutants: A high concentration of air pollutants has the potential to overwhelm the photocatalyst leading to the escape of pollutants and harmful intermediate chemicals in the air cleaner’s exhaust air. The concentration of pollutants can be reduced by pre-filtering air before it enters the catalytic chamber of the device.
  3. The rate of airflow through the air cleaner: The movement of air through the cleaner has to be slow enough to provide contact between pollutants in the intake air and the activated titanium dioxide catalyst. 

Advantages and disadvantages of PCO air purifiers

The concept of PCO is a promising one, but PCO technology does have notable limitations that are important in evaluating it as an air purifier. Here are some advantages and disadvantages of 

PCO air purifiers:

Advantages of PCO air purifiers

Here are the key advantages of the PCO air purifier:

  • PCO air purifiers can remove particulates and gaseous pollutants from indoor air: The free radicals generated by PCO air purifiers operate at the molecular level to destroy bonds in particulate and gaseous air contaminants. This makes PCO air purification an excellent choice for degrading volatiles that includes halogenated hydrocarbons, olefins, aromatics, alkanes, and aldehydes.
  • PCO can reduce ventilation costs for large buildings: PCO eliminates harmful gases and particulates, reducing their concentration in room air. By reducing the concentration of pollutants with PCO, building and facilities managers don’t have to increase ventilation to improve indoor air quality saving energy and money. 
  • PCO air cleansers can eliminate odors: Photocatalytic oxidation efficiently destroys volatile organic chemicals that cause unpleasant odors in indoor environments.
  • Photocatalytic oxidation can be combined with other air purification technology to enhance the cleaning of indoor air: Many PCO devices include HEPA filtration to remove particulates before intake air enters the catalytic chamber. They may also contain chemisorbent media to remove any unconverted pollution from the exhaust air of the device.
  • PCO air purifiers are typically quiet: PCO air purifiers do not move air quickly through their catalytic chamber, ensuring that the air pollutants have maximum opportunity to be oxidized and destroyed. This means that the sound generated by these devices as they operate is not intrusive.
  • PCO air purification provides suitable air disinfection for high-cleanliness environments: These air purifiers are capable of destroying pollutants that could contaminate sensitive environments like operating theaters, or manufacturing facilities for electronics.

Disadvantages of the PCO air purifier

Important disadvantages of PCO air purifiers include:

  • A PCO air cleaner does not destroy all pollutants: PCO air cleaners cannot degrade carbon monoxide, radon gas, ozone, and many inorganic air pollutants. 
  • The photocatalyst media has a finite lifespan: The titanium dioxide-coated filter media of PCO air cleaners does not perform indefinitely. The catalytic module in these devices needs to be replaced at regular intervals to ensure that they maintain safe and efficient performance. 
  • PCO has variable efficiency in removing devices: As an emerging technology, the performance of PCO devices is highly variable. Research has shown that the efficiency of pollutant removal can vary between 20% and 80% depending on the PCO air purifier used. 
  • PCO air purifiers have no national or international efficiency standards or performance metrics: Standardization is essential for the objective evaluation of air purifiers. This means that consumers are largely reliant on manufacturer claims of efficacy and safety. The Environmental Protection Agency has cited the lack of evidence and standards for the performance of PCO devices as a safety concern. 
  • PCO air purification may not completely transform gaseous air pollutants: Several studies of PCO air purification technology have found that the conversion of VOCs by PCO air cleaners is often incomplete. This leads to the generation of hazardous intermediate chemicals including nitrogen dioxide, formaldehyde, carbon monoxide, acetaldehyde, and ozone.

Are PCO air purifiers better than HEPA air purifiers?

HEPA air filtration is an industry-standard, removing at least 99.97% of particulate air pollutants that have a diameter of 0.3-micrometers. Though it cannot remove gaseous air pollutants, HEPA has a strong reputation for its efficient, reliable, and safe performance. 

PCO offers the promise of degradation of organic particulates and gasses, making it ideal for removing a wider range of pollutants from indoor air. However, the performance of PCO air purifiers may not always be consistent, meaning that HEPA may be the better choice for certain applications.

Is PCO the same as PECO?

Photoelectrochemical oxidation or PECO is a related air purification technology that is based on PCO. It was developed in the 2000s by Dharendra Yogi Goswami, an engineering professor from the University of South Florida. 

PECO addresses the inconsistent performance of PCO air purification by augmenting the generation of free radicals with an electrical current. The higher concentration of free radicals ensures that pollutants are degraded more completely and prevents the emission of pollutants in an air purifier’s exhaust air.  

You can learn more about the differences between PECO and PCO air cleaners in the article “PCO vs PECO Air Purifier” [INSERT LINK from the article when published].

In conclusion

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Photocatalytic oxidation devices can deliver outstanding air purification performance, but they must be carefully designed and calibrated to operate efficiently and safely. The limited independently-verified evidence base and lack of formal guidance and recommendations make it hard to evaluate these air purifiers. However, many PCO air purifier models have features like pre-filters and chemisorbent materials that improve their efficiency and safety.