Historically, ultraviolet (UV) light has been used to disinfect water, surfaces and the air. You may wonder if this technology works against airborne microbes or generally improves the air quality of your home. This article will describe how UV air purifiers work, whether they have been shown to be effective in cleaning the air and their potential safety concerns.
What are UV light air purifiers?
UV air purifiers are designed to use short-wave ultraviolet light (UV-C light) to inactivate airborne pathogens and microorganisms like mold, bacteria and viruses. They have the same ultimate goal of all air purifiers: to reduce indoor air pollutants. The technology is also referred to as UV germicidal irradiation, or UVGI air purifiers. This is different from other air purifier technologies that contain UV light technology but do not use it directly against air pollutants.
On the market, UV-C air purifiers are currently sold as stand-alone, freestanding devices or as systems installed into pre-existing residential or commercial HVAC units. As air is forced through the device, it passes UV lamps, which directly attempt to disinfect the air by means of germicidal irradiation. The biggest safety concern is that ozone may be generated during this process.
Rarely a stand-alone product, UV-C light air purifiers often require additional systems for full effectiveness and are most often included in larger High-efficiency Particulate Arrestance (HEPA) air filtration systems. In fact, the EPA says that a UV-C air purifier does not seem effective as a stand-alone unit because it cannot trap or remove particles.
Background on ultraviolet light
Germicidal UV light has been used in the treatment of tuberculosis and to disinfect hospitals, kitchens, meat processing plants and laboratories. As long ago as 1908, UV-C light was used to disinfect municipal water supplies in France.
Electromagnetic radiation takes on many forms–from visible light to radio waves to ultraviolet light. Here is some background on how different forms of light have different energy levels:
Different forms of light
Light is made up of tiny particles called photons. As they travel, they vibrate back and forth and trace a wave in space. The quicker they vibrate, the shorter the distance between each wave. The slower the vibration, the longer the distance between each wave. This wave-to-wave distance is called the light’s wavelength. Long waves with slower vibrating photons have less energy. Short waves with quicker vibrating particles have more energy.
Depending on their molecular makeup, different materials in the world reflect and absorb different wavelengths of light:
- Visible light has a wavelength between 400-700 nanometers long—the range that affects the light receptors of your eyes.
- Infrared light, which you can feel as heat, is longer (700 to 1M nanometers).
- Ultraviolet, which you cannot feel or see, is shorter than visible light at 100 to 400 nanometers.
Photons transmit electromagnetic energy when they encounter matter, and ultraviolet light has high levels of energy.
Ultraviolet light: UV-A, UV-B and UV-C
Ultraviolet is split into three sections:
- UV-A light: 315–400 nanometers with photons that vibrate just a little faster than visible light
- UV-B light: 280–315 nanometers, with photons that vibrate even faster
- UV-C light: 100–280, with photos that vibrate the fastest and carry the most energy
Prolonged exposure to UVC light can cause temporary eye and skin damage, so extra precautions should be taken if directly working with or around UVC lamps. Today, UV light is mainly used to complement other established methods of disinfecting and “sterilizing” sensitive scientific and medical equipment and spaces, though such irradiative cleaning systems have found their way into residential and commercial applications by UV light’s popularization as a purifier in the past two decades. These products fall within the scope and exigency of improving cleanliness and reducing environmental pollution, rather than combating infectiousness.
How do UV light air purifiers use UV-C light?
UV-C light is responsible for the main disinfectant activity of UV-C air purification systems. All that extra energy, much more than visible light, can actually change the molecules that absorb it, and DNA is particularly susceptible to these changes. Ultraviolet light bombards microorganisms around the UV lamp and damages the DNA they need to live.
When people get sunburned after a day at the beach, they are suffering radiation burns from a type of UV light emitted by the sun—the redness is the inflammatory response of the skin when its DNA is directly damaged by UV radiation, which can potentially lead to skin cancer.
Since bacteria are only one cell, they rely on their DNA to live. This is the principle behind UV light air purifiers. If a bacterial cell’s DNA is sufficiently damaged, it triggers a self-destruct mechanism, rendering it harmless.
UV-C air purifiers can be installed in a wide variety of ways and to varying degrees of success (Macher, 1993). In one study, the placement of germicidal ultraviolet lamps on the walls of healthcare dwellings was found to successfully provide the disinfectant qualities with no statistically significant side-effects of UV overexposure, reinforcing the familiarity these systems have in the healthcare industry (Nardell et al. 2008).
How do UV air purifiers clean the air?
The way UV-C light air purifiers work is quite simple. As discussed above, they are designed to use UV lamps that can potentially alter the DNA of microorganisms and inactivate or destroy them. Depending on the material of the emitter (e.g., phosphor or quartz,) this light may be blueish or may not be visible to the human eye. Usually, residential units use mercury lamps that emit UV-C light at a wavelength of 254 nm, according to the EPA.
UV light air purifiers are generally a combination of a forced air system and another filter (like a HEPA filter). As a result, the UV light of the air purifier acts together with other processes to clean the air. Ambient, in-house air is forced through the unit and ventilated through a chamber with bulbs emitting light within the UV-C frequency. The UV lamp is usually placed downstream of a filter in a portable air purifier. Various factors such as the type of UV lamp, humidity and temperature can affect its performance.
UV-C lamps used in UV-C germicidal purifiers are silent, and the glow of many, depending on the casing mounted around it, is invisible to the human eye. They are generally odorless. UV bulbs may need replacing on a yearly basis, depending on the make and model.
Dangers of UV air purifiers
Perhaps the most important negative aspect of UV air purifiers, UV-C radiation has been proven to transform the oxygen in the air into ozone (Slonim et al, 1969). This happens through photolysis–when light causes oxygen (O2) to break apart into two individual atoms and combine with other oxygen molecules to create ozone (O3). This can happen with the UV-C lamps mentioned above, especially if they are uncoated. Because of this possibility, some manufacturers use a special coating on the UV lamps.
How effective are UV air purifiers?
Though UV-C light can potentially deactivate microbes, whether it can do so within a portable air purifier unit is a different matter altogether. These units are often advertised to reduce dust mite and mold allergens.
The effectiveness of UV-C light in disinfecting the air depends on a number of factors, including:
- Whether the pollutants come into contact with the UV light
- Whether the light is inhibited by the cooling effect of airflow
- The material of the bulb emitting such light
- The high dosage of light required
- How long the pollutant is exposed to the light
UV air purifiers vs. microorganisms
If it is properly designed, the UV filtration process can potentially deactivate some bacteria and mold and offer a small reduction in viruses, but little reduction in bacterial and mold spores (Kowalski & Bahnfleth, 2000). Generally, bacterial and mold spores are resistant to UV radiation and require a high dosage of UV light. The EPA says that for actual destruction of mold and bacteria spores, you would need high levels of UV light and much longer exposure times. You may need much higher levels that what is offered in a residential unit, as well as prolonged exposure–much more than the few seconds when air passes through a device.
UV air purifiers vs. allergens
UV purification does not entirely remove allergens, chemical fumes, dust, pet dander, cigarette smoke or molds from the air (Olander et al., 1988). Dangerous gases and many solid particles are often invulnerable to UV radiation.
The EPA says that mold particles can still cause allergies even when deactivated, and so UV air purifiers may not be effective for allergies and asthma.
UV air purifiers vs. VOCs
Many harmful pollutants are unaffected by UV-C light. UV light cannot destroy volatile organic compounds, or VOCs – commonly found in household products, from paint and varnishes to cleaning, disinfecting, and cosmetic solutions. The intense energy of UV light can even cause VOCs to off-gas more quickly than they usually would, or change them into more dangerous substances.
If a UV air purifier on the market produces ozone, it can create a health risk for you and your family in your home. If there is no risk of ozone, UV-C light air purification systems may offer some type of disinfection capability, though it should have a filter media to trap particles as well. Generally, studies have shown that portable UV-C light air purifiers have limited effectiveness against microorganisms and cannot address many pollutants like VOCs.
There has been little innovation in the air purifier industry until now. A new technology, Molekule PECO technology, offers a powerful alternative solution over UV air purifiers. Not only does PECO technology destroy airborne microorganisms, it also destroys VOCs and allergens that UV air purifiers cannot address.
Aerosol Research and Engineering Labs tested PECO technology against a highly resistant bacteria, Staphylococcus epidermidis. The lab also tested the technology against viruses, mold and endospores. Results showed that PECO reduced concentrations of microorganisms by 99.99%.
Unlike UV-C air purifiers that attempt to deactivate microbes, PECO technology can destroy them. Most importantly, the PECO process does not produce ozone, as verified by an independent ozone emission test report. Learn more about the Molekule air purifier here.