UV air purifiers — how do they work?

Ultraviolet (UV) light over decades has been used to disinfect surfaces, water and the air. Lately, the technology behind UV air purifiers has been used to improve the air quality around us.

But do UV air purifiers defend us against airborne viruses, and how do they work?

Concerns surrounding air quality and a public increase in health awareness due to the COVID-19 pandemic have led to increased demand for the use of UV air purifiers. According to a Research and Markets study, the global air purifier market size will reach USD 31.83 billion by 2027.

Several air purifiers on the market exist that reduce airborne contaminants, like viruses, in the home, offices and commercial places. Fighting airborne viruses has become a much-sought demand since airborne transmission has been proven to transmit COVID-19, especially in indoor, enclosed and crowded spaces with little ventilation.

But are these UV air purifiers effective?

Here’s what to know about UV air purifiers, how they can help with indoor particles and pollutants, and whether they can protect you against COVID-19.

What are UV air purifiers?

UV air purifiers are designed to use shortwave UV-C light to inactivate airborne pathogens and microorganisms like mould, bacteria and viruses.

UV air purifiers have the same goal as all air purifiers: to reduce and remove indoor air pollutants. However, UV technology is different from other air purifiers in that rather than only removing air pollutants, they inactivate them, thus, making the air around them cleaner, safer and better for all.

The current UV air purifier consists of two device types:

• standalone or freestanding devices
• personal and wearable devices

Standalone UV air purifiers

A standalone UV air purifier is air quality control equipment that uses UV-C light to rid the air of harmful bacteria, viruses and other pathogens within a room to make the air clean and safe to breathe.

Home and office UV air purifiers usually come in a small, compact form. Still, some models are larger than others but please note that it can take more time to purify air room quality depending on the model. Some contain mercury lamps and don’t always use more effective UV-C LEDs.

Rensair is an example of a standalone UV air purifier. Genano does not use UV-C but plasma technology. Both still use HEPA filters that need cleaning and replacing.

Wearable or personal UV air purifiers

A personal UV air purifier offers faster protection once the device is switched on. It protects the wearer instantly and does not need to wait for a room to be purified. Plus, the wearer can switch locations without purifying a new room or moving a standalone air purifier. Wearable UV air purifiers that do not use filters will not get clogged up or dirty, so no filters need to be changed.

Wearable UV air purifiers are part of a hybrid solution inactivating harmful airborne viruses, microorganisms, and pathogens without wearing a mask. As they are reusable, unlike masks, they are also more sustainable.

Respiray is one example of a wearable air purifier.

UV air purifiers vs HEPA air purifiers

No air purifier is perfect and without flaws. Similarly, both HEPA filters and UV-C light air purifiers come with their own set of benefits and disadvantages.

UV-C air purifiers kill and do not catch airborne viruses as HEPA devices do. HEPA only collects viruses, bacteria, allergens and spores instead of destroying them; therefore, filters need to be replaced regularly. There is little to no maintenance with UV-C.

UV-C devices are, however, more sustainable and energy-efficient (especially when they use new generation LEDs that are very energy efficient). HEPA devices need frequent filter changes, but UV-C LEDs last around 3.5 years, depending on the usage and the LED operating hours.

HEPA filters are not compostable. The only way to provide biosafety of HEPA waste is to burn it. Also, when changing the filters, they could be full of viruses and spread to the cleaner.

HEPA filters are more effective for allergy sufferers as they remove air pollutants and are potentially cheaper than standalone UV air purifiers. Wearable UV air purifiers are more cost-effective, cheaper, and reusable.

Plus, with both HEPA and UV standalone air purifiers, it depends on the room size and how effective it is, taking up to an hour to eliminate viruses.

A personal air purifier device like Respiray needs to purify only the air a person breathes rather than the whole room. The Air Change per Hour (ACH) is around 30x higher than World Health Organisation recommendations.

How do UV air purifiers work?

As air flows through the devices, it passes through UV-C technology that directly eliminates the airborne pollutants employing germicidal UV light. The biggest safety concern is that UV light may generate ozone during this process (these fears have developed from the early UV mercury lamps used in the mid-twentieth century).

Direct exposure to UV-C light is dangerous to humans. However, in leading personal devices like Respiray, UV-C light is sealed inside, so no UV-C light is exposed to humans. Today, reputable UV air purifiers have UV-C light contained within devices that emit no ozone, making them safer to use.

Why UV light is used for disinfection

UV disinfection uses ultraviolet light to clean and disinfect air, water or surfaces.

UV light is part of a spectrum with wavelengths varying between 200–400 nanometres (nm), just below wavelengths visible to humans.

The UV spectrum is divided into three different wavelengths:

UV-A rays have the longest wavelengths, followed by UV-B and UV-C rays which have the shortest wavelengths.

Whilst UV-A and UV-B rays are transmitted through the atmosphere, the Earth’s ozone layer absorbs UV-C and some UV-B rays. Thus, most UV rays you come in contact with are UV-A with a minor amount of UV-B.

UV-A and UV-B are either not at all or partially absorbed by the ozone layer; UV-C is fully absorbed. Because no UV-C from the sun reaches the Earth, no viruses, bacteria and other pathogens have not developed resistance to it.

The technology of using UV for disinfection is known as ultraviolet germicidal irradiation, or UVGI for short.

UV-C light is mainly used to complement other established disinfecting methods and ‘sterilise’ sensitive scientific and medical equipment and spaces. However, in the past two decades, such irradiative cleaning systems have found their way into residential and commercial applications by UV light’s popularisation as a purifier.

These products fall within the scope and necessity of improving cleanliness and reducing environmental pollution rather than combating infectiousness.

Can UV-C light kill pathogens?

UV-C lamps have long been the traditional products associated with killing bacteria and viruses.

They are often called germicidal lamps. Their ability to inactivate airborne microorganisms was first known in 1937, preventing an epidemic spread of measles in schools in Philadelphia.

UV-C light is one of the most effective methods of eliminating harmful pathogens as UV-C light doesn’t get through the earth’s atmosphere. This means no bacteria and viruses have developed resistance against it. UV-C light damages the DNA and RNA of harmful pathogens, so they cannot multiply.

UV-C lamps began to be used in hospitals, either fixed to walls and on trolleys bathing the wards and corridors with UV light, a practice used to deep-sterilise areas usually full of ill patients, cross-contaminated medical staff and well-used equipment.

How do UV air purifiers clean the air?

The way UV air purifiers work is relatively straightforward.

As discussed above, they used to be UV-C mercury lamps. However, today, most, including our own device, use UV-C LEDs as they are safer and more effective to alter the DNA of microorganisms and inactivate or destroy them.

UV air purifiers are generally a forced-air system and another filter (like a HEPA filter). As a result, the UV-C light of the air purifier acts together with other processes to clean the air.

Airflow is passed through a unit within the UV air purifier and ventilated through a module or chamber with LED bulbs emitting light within the UV-C frequency. The UV LED, or UV lamp, is usually placed downstream of a filter in a portable air purifier.

UV-C lamps or UV-C LEDs used in UV-C germicidal purifiers are silent. Depending on the casing mounted around it, the glow of UV light is invisible to the human eye and is odourless. UV lamp bulbs may need replacing yearly, depending on the make and model, but UV-C LED technology (like in Respiray) lasts 3 to 3.5 years depending on the usage

But aren’t UV air purifiers dangerous?

UV-C light has been used for decades to disinfect air, surfaces and water to reduce the spread of viruses and bacteria. UV-C light that doesn’t reach the Earth is ultimately very effective at eliminating harmful pathogens and is carcinogenic.

This means that, yes, direct exposure to UV-C light is dangerous to humans. However, the UV-C light is sealed inside devices, so no UV-C light is exposed to humans.

Whilst at some wavelengths, the energy of UV light can produce ozone, this only happens below 242 nm and this is also confirmed by the European Commission. UV-C light is generally associated with UV-C mercury lamps. Some UV-C lamps cause ozone and other radicals due to multiple emitted wavelengths — this is likely what many associate the dangers of UV-C with.

Reputable companies have protective measures in place to ensure the safety of their devices. For instance, in Respiray’s wearable air purifier, there is a double UV-C resistant plastic enclosure around the UV-C emitting LED. Our team has carried out ozone tests with a laboratory affiliated with Tartu University for additional safety. The results showed no ozone production.

How effective are UV air purifiers?

Because UV-C light can potentially deactivate microbes, they can be very effective in combatting the spread of airborne viruses. It’s why German, Estonian and UK schools have begun to invest in UV technology to keep children and teachers safe and schools open.

However, we should state that the effectiveness is dependent on what type of device they are and several factors, including:

• do the viruses and bacteria come into contact with the UV light?
• how long are the pathogens exposed to UV light?
• the location of the device (around a wearer or in a room or on a wall)
• which type of UV device is it — lamp or more effective LEDs
• time taken to begin air purification (standalone units take some time before they purify a room, more wearable devices disinfect immediately)

It’s imperative to ask these kinds of safety questions when considering purchasing a product that uses UV-C technology. Ensure that the manufacturer has all the safety measures in place and check whether they have scientific proof of their effectiveness.

When we started to develop the Respiray wearable UV air purifier, safety was paramount. We have conducted research and tests and worked closely with scientists across different universities to design a social, sustainable, and, most importantly, safe wearable air purifier to protect people.

Want to know more about Respiray and how it protects you against harmful pathogens? Check out the benefits of our wearable UV air purifier.

Originally published at https://respiray.com on November 10, 2021.