Air Purifiers

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FAQ about Air Purifiers:

• Why buy an air purifier?
• What is an air purifier?
• What types of air purifier are there, and how do they work?
• What should I look for when buying an air purifier?
• Which type of air purifier will remove particle pollution?
• Which type of air purifier will remove chemical pollution?
• Which type of air purifier will remove particle pollution?
• How reliable are claims made by air purifier manufacturers?
• What standards and tests are applied to air purifiers?
• What evidence is there that air purifiers can actually benefit health?
• What should I consider when buying an air purifier?
• What pollution should an air purifier filter out?
• Is UV light recommended in an air purifier?
• What is an air washing air purifier?
• What are ozone air purifiers?

 

Why buy an air purifier?

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A good air purifier can significantly improve indoor air quality by removing virtually all particle pollution. These include house dust mite, mould spores, pollen grains and PM₁₀, PM_2.5  and ultrafine particle pollution from traffic and industry. An air purifier can also remove molecular pollution like gases, including cigarette smoke components and volatile organic compounds. Which components of your indoor air pollution are removed will depend upon the type filtration the air purifier uses. Some combine filter and absorbent technologies so they can remove both particles and gases from the air. Finding the right air purifier for your needs whether, for instance, you have a child with asthma or suffer yourself with chemical sensitivity, can be difficult. There are hundreds of different types, manufacturers make various claims, which are not yet properly regulated.  There are, however, some excellent air purifier models available, endorsed by opinion leaders within the industry and used in hospitals, research facilities, and government buildings around the world. These air purifiers will protect your family's health and can make a real difference to those who suffer from allergies, multiple chemical sensitivities, asthma, and other respiratory problems. 

What is an air purifier?

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An air purifier is a device which removes particulate and/or gaseous pollution from the air. They range widely in size and design, from large installations used on an industrial scale to small portable machines that could be used in a bedroom. Residential air purifiers are either stand alone or whole house air cleaning systems. 

There has always been a percieved need for cleaning the air. For instance, Leonardo Da Vinci had the notion that finely woven cloth dipped in water would protect the military from toxic powders.  At the end of the 18^th century, the German explorer and naturalist Alexander von Humboldt devised a primitive respirator for use in mining, while Lewis P. Haslett’s ‘lung protector’, which received its patent in 1848, used moistened wool with a one way valve to filter dust out of the air.  The High Efficiency Particulate Air (HEPA) filter system was developed by the United States Army Chemical Corps and the United States Atomic Energy Commission during the Manhattan Project (development of the atom bomb) to protect against the spread of radioactive dust. The first HEPA filters were rigid and unwieldy machines, quite unlike their modern counterparts.   

What types of air purifier are there, and how do they work?

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There are many systems and models available, but they fall into four basic categories, described below:

HEPA Air Purifiers

The US Environmental Protection Agency recommends HEPA (high efficiency particulate air) filters as the most effective of the mechanical air purifiers. The HEPA is a specialized filter consisting of a folded mat of fibres. It has three different modes of action, each of which acts upon a different size of particle. Interception deals with particles above 0.4 microns in diameter and involves the particle sticking to a fibre in the HEPA filter when it comes close to it. In impaction, the particle is blown towards the fibres by the airstream on which it is travelling, collides with them and sticks to the mat. Then there is diffusion, which mainly affects smaller particles, of diameter below 0.1 microns. The particle collides with air molecules which throw it off course. Diffusion keeps the particle within the filter until it is captured by impaction or interception. What about particles between this size range? They are captured, but with a very small decrease in efficiency.  

HEPA air purifiers uses the same principle as a spaghetti strainer- it holds back everything that is too big to fit through it's mash. The benefit of this kind of filtration, is that it does not lose its filtration efficiency over time. A true HEPA filter becomes more efficient in filtering air pollution, the more pollution loads up in the filter. The airflow delivery rate of an air purifier using mechanical filtration might decrease, but the filtration efficiency will increase. This makes mechenical HEPA filtration the most reliable filtration technology, because you know that the air that goes through the filter is always cleaned at the same rate.

The term “HEPA” filtration is unfortunately not properly regulated. Every manufacturer can use the term "HEPA filtration" as they please. So you should look at independent testing for the actual performance of an air purifier before purchasing it. A drawback of true HEPA filtration is that the air purifiers tent to be larger then other air cleaners, such as an ionizing air cleaner. The larger size of a true HEPA air cleaner is required in order to be able to provide a desired air-flow rate. 

It is a little known fact that a air purifier such as the IQAir HealthPro 250 virtually takes all particles out of the air.  Only at the range of 0.3 microns, particle movement is so erratic the 0.05% of them will not be captured.  There is no other domestic air purifier that comes close to this kind of filtration efficiency.  

Electronic Air Purifiers

Electronic air purifiers work by giving particles that pass through the unit an electric charge and then using electrostatic attraction (positive attracts negative and vice versa) to trap the particles. There are different kinds of electronic air purifiers; two popular versions are electrostatic precipitators and ionizers. The electrostatic precipitator sucks air into the unit, charges up the particles in the first section, and then passes the stream to a pair of plates bearing an opposite charge. So the particles stick onto the plates. An ionizer acts externally rather than internally in that it releases ions into the environment. This charges up the particles in the air and they become attracted to their surroundings by electrostatic attraction (ever tried rubbing a balloon on your jumper and making it stick to the wall, or curtains? You’ve got the idea!). A problem here is that electrically charged pollution can be an inconvenience when it sticks to walls, furnishing and other objects in your house. For that reason we do not recommend air purifiers that use ionization alone and do not combine it with a HEPA-like filter as Blueair does. 

A common problem with ionizing air purifiers is that the collection efficiency with which the air purifier collects the pollution out of the air should be as high as possible. All air pollution that is ionized when passing through the air purifier, but that is not collected in or on the air purifier's collection surface will attach itself to something else with in your home. So if the air cleaners collection efficiency is only 80%, then you are realising 20% of charged air pollution particles into your environment.

Another problem with air purifiers that use ionization is, that their filtration efficiency tend to get less effective with use. Many ionizsers might start out with a particle collection efficiency of 90% or even 99%, but that efficiency can often drop quickly to as low as 50% or less. The reason that the collection efficiency decreases, is that if enough dust is accumulated on the air cleaner’s collection surface, then that dust functions as an insulation. The charge will not pass through the layer of dust, letting the particle pass through the collection surface without being captured.

To ensure that your ioniziser is working most efficiently, you should make sure that its filters are replaced regularly and often enough.

UV Air Purifier

Ultra-violet (UV) light is very short wavelength radiation which kills living particles like viruses, bacteria, and moulds (generally known as microorganisms) if they are exposed to the light for a significant amount of time. The performance in terms of killing microorganisms with an UV light depends upon the dose of UV light to which the air pollution is exposed, the actual length of time the microorganisms are exposed to the light, and the nature of the microorganism involved (not all bacteria are killed by UV, nor are mould spores). In general, microorganisms have to be exposed to UV light for several hours to be killed. Given that the air passes through an air purifier within a fraction of a second, UV light is not an effective way to eliminate microorganisms from the air.  

Gas / Chemical Air Purifier

What if you’re concerned about volatile organic compounds (VOCs) rather than house dust mite allergen or other particles? These are gaseous molecules, rather than particles, and none of the above air purifier types by themselves will remove them. VOCs, as other chemicals, are removed by purifiers containing activated granular carbon, or equivalent, filters. Important here is the quality of the carbon that is being used. Carbon dust (which is relatively cheap) will not be very effective. Some air purifiers, like the IQAir HealthPro 250, combine a HEPA filter with a powerful gas filter, thereby removing the widest range of pollutants.  Alternatively, you might want to consider a IQAir GC VOC or IQAir GC MultiGas for environments with elevated chemical contamination.  

What should I look for when buying an air purifier?

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There are several factors you should consider, described below.

• Stand alone or whole house system? Stand alone air purifiers are easy to use and install, allow you to focus on one room or area at a time, and tend to achieve higher filtration efficiency. 
• Whole system efficiency. The efficiency of an air purifier is described as its Minimum Efficiency Reporting Value (MERV) which is a number between 1 and 20. The Environmental Protection Agency translates this as follows: True HEPA filters with a MERV between 17 and 19 are defined as having a minimum efficiency of between 99.97% and 99.999% in removing 0.3 micron particles.  An air filter with a MERV value of 7-13 might be almost as effective as a 'true' HEPA filter and will be quieter and less expensive. This efficiency may not be achieved in practice if there are leaks present, if the filter is damaged or becoming worn. 
• Air change per hour rate. Put simply, this is how fast the air purifier processes air going through it (polluted air in, clean air out). This is measured by the room's volume in cubic meters divided by the air purifier's airflow rate in cubic meters per minute.  You might want to look at an air purifier that gives at least 2 air changes per hour to be effective at lowering pollutant/allergen burden.
• Filtration technology. As described above, there are HEPA and electrostatic filters with the former generally being more efficient.
• Maintenance cost. Consider how often you will have to change filters and parts. 

Which type of air purifier will remove particle pollution?

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The HEPA and electrostatic air purifiers remove particle pollution.

What type of air purifier will remove smoke and chemical pollution?

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An air purifier fitted with activated carbon filters will remove smoke and chemical gaseous pollution. For instance, the IQAir HealthPro  250 contains both a HEPA filter (a HyperHEPA filter which filters out particles down to 0.003 microns) and activated carbon and impregnated alumina filters to remove a wide range of gases and odours.

How reliable are claims made by air purifier manufacturers?

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Labels and claims on air purifiers are often no more than marketing slogans. Look, therefore, for independent testing and endorsements. Be aware, however, that some supposedly independent tests and certifications are again just companies run indirectly by certain a manufacturers. You should also be aware that there are a lot of dealers and distributors that only push products to make money, but do not undertand the products and the industry.  Look for dealers that know what they are talking about.  Just because someone is selling air conditioners does not mean that they understand air purifiers. 

What standards and tests are applied to air purifiers?

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Various types of performance standards are set for air purifiers, though none are universally used. One is called the Military Standard 282 which is used to rate particle reduction in air purifiers fitted with HEPA filters. Another which is used with home air purifiers is the ASHRAE which tests how many larger particles can be removed from the air, and also the amount of dust left on the filter when the air has been filtered through the unit, which gives an idea of how long the filter might last. 

Another test for the efficiency of the effectiveness of HEPA filters is the DOP penetration test, which sends a cloud of particles 0.3 microns in size through the filter and comparing how highly concentrated these particles are in the airstream before and after they pass through it. 

What evidence is there that air purifiers can actually benefit health?

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There have been a number of studies, described below:

• Children with asthma exposed to second hand smoke had fewer emergency hospital visits when their homes were fitted with a HEPA filter.
• HEPA filters in hospital rooms decrease the rate of invasive aspergillosis.
• Fitting a HEPA filter in the home was found to reduce cardiac disease markers while also reducing levels of particulate pollution.
• In chronic obstructive pulmonary disease, many doctors do recommend air purifiers as part of a medical management strategy which also includes inhalers, antibiotics, and steroids.

What should I consider when buying an air purifier?

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There are several aspects that you should consider when buying an air purifier. One of the most important aspects is effectiveness. The effectiveness primarily depends on:

1. the amount of air the air cleaner moves, and
2. the air cleaner’s efficiency in removing air pollution from the air.

If you are looking for a unit that is supposed to filter out the two different kinds of air pollution in your home, you will need to make sure to take a machine that has effective HEPA filtration as well as gas filtration.  

Another thing you should keep in mind is, that there are many dubious air purifier manufacturers, and they are not affright to blatantly misrepresent information. The result is that many labels and certificates for air purifiers that you find in stores and online are nothing more then well devised marketing programs in disguise.

What pollution should an air purifier filter out?

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Air pollution either consists of gas or particulates. Particle pollution can have many sources, such as tobacco smoke, pet allergens, microorganisms, pollen, spores, dust mite allergens. Gas pollution is caused by cleaning products, sprays, solvents, paints, vanishes and adhesives. To learn more check out our Air Pollution page and Air Pollution Chart. It is important to point out that are the different kind of technologies that have to be used to collect particle pollution on the one hand, and gas and chemical pollution on the other hand.

What is an air washing air purifier?

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Air washing air purifiers can be effective for removing larger particle pollution from the air. A problem, however, tends to arise whenever one combines water and bacteria/dirty air, which naturally results in growing more contamination. To avoid a hygiene issues such as mold growing in your air cleaner, it is advisable to use chemicals to fight bacterial growth. It is important to keep in mind, however, that some of these chemicals will be released into the air when the water in the air washer air purifier evaporates. Inhaling these chemicals can result in severe reactions in people with respiratory conditions.

What are ozone air purifiers?

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Ozone can clean the air by affecting the cells that are exposed to it. This makes ozone very effective in cleaning bacteria and mould infestations in hard to reach places. Ozone, however, does not discriminate one cell against another. It will affect a person’s lugs in the same way that it is affecting bacteria that it is supposed to get rid off. For that reason, ozone has absolutely no place in everyday air purification in a domestic setting. Ozone should only be used to clean the air if no humans or animals are around. Some ionizing air purifiers are producing small amounts of ozone. The ionizing process breaks down oxygen molecules in the air, producing ozone in the process. There have been ionizing air cleaners that have been banned for those reasons.