Air purification is becoming an essential step in taking care of our health. PCO air purifier are – by far – the most effective technology to fight indoor air pollution.

The application of photocatalytic oxidation in the processes of cleaning both air (PCO Air Purifier) and water is an exciting and recently discovered technology. This new technique is at the core of the wave of novel air purification devices commercialized by several different companies in recent years. All these technologies have a few similarities, as they mostly “process” pollutants on a photoreactive surface that utilizes photons of light to initiate a reaction which oxidizes and destroys organic pollutants in the air.

Photoreactor air purifiers perform, typically, a form of Photocatalytic Oxidation (PCO).

What is photocatalytic oxidation?

Air purification through photocatalytic oxidation is a process that involves a light-activated catalyst reacting with organic pollutants to oxidize them. Fundamentally, air pollutants are sucked in the device where they go through a chemical reaction that ultimately transforms them into non-toxic substances.

Since the 1990s, several hundreds of papers have been published on the possibility of using this process to clean the air and water from toxic pollutants. And in the most recent years there has been a lot of interest revolving around this groundbreaking technology, as it becomes more and more mainstream and more products are brought to market.

PCO – basically – works by combining ultraviolet (UV) light with titanium oxide, usually applied as a coating to a filter. The photocatalytic process emerging from the contact of the two, results in the formation of hydroxyl radicals and superoxide ions, both highly reactive electrons.

These “supercharged” electrons have the ability to electrically “attract” volatile organic compounds and bacteria floating in the air, combining with them.

Some volatile organic compounds get attached to hydroxides and hydrogen radicals during the oxidation process. Other pollutants like bacteria and fungi are destroyed by the incorporation of a photon with ultraviolet light rays.

Regardless from when it happens, this reaction greatly accelerates the breakdown of pollutants in the air into harmless products like carbon dioxide (CO2) and water molecules.

Photocatalytic process in PCO air purifiers

Here are the main components used in any photocatalytic process:

Photocatalyst

A photocatalyst is a substance that enables a chemical reaction to happen on its surface when activated by light. In PCO air purifiers, this chemical reaction is used to break down pollutants. Most PCO air purifier use a slightly different catalyst, with varying degrees of effectiveness, safety, durability, and environmental impact.

Free Radicals and Reactive Oxygen Species

All photoreactor processes use photons of light to free electrons from the surface of the catalyst, leaving “positively-charged holes” in the catalyst where electrons used to be. Hydroxyl ions (OH-) form naturally from water vapor in the air and carry a negative charge. These ions react with the positive holes on the catalyst surface by inserting one of their electrons in the “hole”, which turns the ions in hydroxyl free radicals.

Hydroxyl free radicals are among the most potent oxidizers in the world, and can oxidize even the toughest organic molecules in the presence of oxygen. The end result of the oxidation process is the conversion of organic compounds into carbon dioxide, water and small amount of gases.

One of the drawbacks of PCO air purification is that due to the recombination of electrons and holes, the PCO process can end-up utilizing only a small fraction of the photons available, which can reduce its efficiency over time. A potential danger of the inefficient process is that some of the older and less advanced systems may yield toxic oxidation byproducts such as formaldehyde due to an incomplete reaction. Nevertheless, if we consider the most modern PCO air purifiers, even these small risks have been completely overcome.

UV light

UV light is used in the photocatalytic oxidation process to excite and activate the catalyst, which begins the chemical reaction needed to break down pollutants. The best PCO air purifiers use low energy UV light (some even work with just visible light, without need of UV) to begin the reaction. While the most common type of light to use for PCO air purifiers is a very energetic band of light (normally UV-C) to initiate the reaction. The risk with UV-C light is that it can produce small quantities of ozone, another potent oxidizer but toxic to living things. Caution should always be used to ensure no people, pets, or indoor house plants are exposed to elevated levels of ozone.

PCO in tackling pollutants

Microbes

One of the photocatalytic process’s key feature is its ability to sterilize microorganisms, preventing them from growing or infecting further. Airborne viruses, bacteria, fungal spores, and fungal fragments are trapped on the catalyst (the filter) where they are subjected to the oxidation by the photocatalytic process.

Microbial cell walls are destroyed through interaction with the free radicals generated on the light activated catalyst surface. Toxins and allergens are also oxidized during this process, so any components of the organism that may cause health problems are safely destroyed.

Toxins are invisibly present in any fragment of microbes. Several studies have been conducted on the oxidative effect of a PCO devices, and they suggest that the process is more than capable of destroying these toxins, converting the cells of the microbes into benign byproduct

Allergens

In addition to microbes, small particles called allergens can also be harmful by causing dangerous allergic reactions that are at best uncomfortable, and at worst can impact productivity and health. The oxidative effect of photocatalysis can break down allergens very effectively, so they don’t stimulate any allergic reaction to begin with.

VOCs

Volatile organic compounds are dangerous to our health, particularly if they come from industrial by-products like paint, furniture, or building materials. VOCs are very vulnerable to oxidation by photocatalysis, though. 

Ozone

Many PCO devices use UV-C light to enable their catalytic reaction. UV-C light is well-known for its ability to convert oxygen to ozone. In fact, the ozone layer in the upper atmosphere is formed from oxygen being exposed to UV-C light emanating from the sun. Modern air purifiers use a different band of UV light called UV-A, which is the same light used in tanning bed bulbs and in the “black light” bulbs that make posters glow fluorescently.

Safety and effectiveness of PCO air purifiers

When considering a photocatalytic system, it is very important to be sure it is efficient enough to not produce any byproducts. There are several factors that influence the efficiency of a PCO device. Engineers have to consider how much light is shining on the catalyst, what types and concentrations of pollutants the device is expected to deal with, the airflow pattern through the device, the moisture levels in the air, and the properties of the specific catalyst used.

There are a few ways a consumer can figure out if a PCO system is safe and effective.

No ozone

The California Air Resources Board (CARB) does not allow air purifiers to be sold in California that produce unsafe levels of ozone, so make sure the PCO system is listed as CARB compliant. All KORU PCO air purifier has been certified and independently tested to not produce any ozone – in fact, KORU’s PCO technology could even be able to reduce the levels of ozone.

Long dwell time

Air pollutants have to spend enough time in contact with the catalyst in order for it to be exposed to enough oxidation, which is normally referred to as the pollutant’s dwell time.

If the system doesn’t seem to capture pollutants and hold them on the catalyst on the first pass, then it might not be completely destroying them. For example, if the pollutants are following an air path that doesn’t carry them directly onto the catalyst, they can easily end up in a region with a lower concentration of radicals. This is particularly problematic with simple organic molecules, such as those found in natural or synthetic fragrance. If partially oxidized, the nice smell of flowers can end up converted into toxic formaldehyde and acetaldehyde. KORU’s air purification technology has been tested to not produce any harmful byproducts.

Research

This is one of the most important aspects to pay attention to when selecting a photocatalytic air purifier. Look for tests done by laboratory companies external to the manufacturer and see how well it can destroy pollutants like VOCs and microbes. If there is no research available, then it’s possible the unit is inefficient at best or totally ineffective at worst. The PCO technology was developed over a period of over 20 years, and took multiple iterations to come to one that is highly efficient and effective in removing pollutants from the air without generating harmful side-products. However, it is currently considered – by far – the golden standard of air purification technologies.

Are PCO air purifier safe?

Indoor air pollutants are harmful materials that pose environmental health risks. Elimination of these pollutant sources will help to improve air quality for inhalation.

Ventilating your home is usually the best option, but most ventilation methods are limited by weather conditions and recurrent air contaminants.

The use of air cleaning appliances happens to be a real, effective solution.

A conclusive note

PCO technology is a fundamental scientific innovation in the air purification industry. Most PCO devices fall short of taking full advantage of the photocatalytic process, by employing low-quality electronical components and filters.

Luckily, the latest advancements in air purification technology allowed us to develop KORU Air Purifier focusing on maintaining an extremely high air purification effectiveness, while limiting our impact on the planet and on customer’s pockets with a permanent and washable filter perfect to capture even up to 99% of virus and bacteria.