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.
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.
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:
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:
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.
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 sanitation. 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).
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.
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.
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:
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 air purifiers are designed to deactivate things like bacteria, viruses, and mold spores, which Molekule destroys. On their own, UV air purifiers do not remove allergens like dust, pet dander, or chemical fumes 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.
Our recommendation
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.
As explained in this article, you need a mechanical filter to go along with the uv light. The uv light only kills the algae, and the filter removes the dead debris from the pond.
And also explained there is that generally the best place the have the uv light is right AFTER the filter:
Generally, the better, and most common, placement is right after the filter. In fact, a lot of the biological filters (that have a uv light built in) place this uv light after the filter itself. There are a couple of good reasons for this:
- The uv light works more efficiently when the water flowing along it is clearer. By filtering out big particles and debris helps, the light can penetrate deeper into the water, and reach more algae.
- Any small rocks being sucked up by the pump and transported to the uv light can harm the quartz sleeve around the bulb. Having a filter before the light prevents damage to the quartz sleeve.
- A filter before the light traps more sludge, thus slowing down the build up of sludge in the uv light casing.
- Ultraviolet light also kills ‘good’ bacteria. Usually this is not something to worry about, because the bacteria tend to live along the sides of the pool and on the bottom. But if some are free-floating, it helps having the filter before the uv light: the good bacteria might stick to the filter material (the pad) itself.
In some cases it might be a good idea to have the filter AFTER the uv light.
In a setting where the uv light is the last stage of the inline filtering process, the killed algae clump together and are then released into the pond. They might sink to the bottom, maybe in a spot where no pump can reach them. What’s not so good about this is that all this biomatter ends up being food for more microorganisms like algae.
Whether or not this is a problem depends on the specific situation of your pond: for example, if you have rocks on the bottom that biomatter will have a hard time being sucked up by the pump, as opposed to a naked plastic liner where any debris is much more likely to be able to swept up.
So, depending on your situation, it can be a good idea to have a filter AFTER the uv light as well as before. That is, of course, if your budget permits this.
That said, if you had to choose between a filter before or after the light, I’d definitely suggest having a filter before the uv light. The pros outweigh the cons.
There’s one type of situation that comes to mind where you cannot do this, where you have to have the filter after the uv. This is when you have a biological filter that spills right off a waterfall.
photo “bio falls”
You can’t have the uv clarifier/sterilizer after these types of “bio-falls”, so in such cases place it before the waterfall.
But in the case when you don’t have such a bio-waterfall (and if your budget permits) it might be worth to place another mechanical filter before the uv clarifier as well.