Table Of Contents
- Common Types of Air Purification Technology
- Removal of Particles
- HEPA Technology
- Electrostatic Precipitation
- Air Ionization
- Removal of Gaseous Pollutants
- Deactivation of Air Pollutants
- Ultra Violet Irradiation
- Photocatalytic Oxidation
- How To Choose An Air Cleaner
- Do Air Cleaners Really Work?
We consider home air purifiers to be green products because they aim to improve indoor air quality which may also contribute to better human health.
It is no surprise that home air cleaners have become so popular, especially among the most sensitive individuals.
What types of air pollution do home air cleaners attempt to remove from our houses?
Air pollutants that pose ongoing risks to our health, and are commonly found in homes, include:
- Dust, fumes and smoke
- Biological contaminants – viruses, bacteria, pollen, molds, dust mite parts, animal dander
Particulate indoor air pollution comes from a variety of sources, such as tobacco smoke and gas stoves.
Dust particles range between 1 and 100 microns (μm) in size, while fumes and smoke are roughly between 1 and 0.01 microns in diameter.
Biological contaminants range from 100 microns (max for pollen) to 0.003 microns (min for viruses) in size.
- Combustion gases, ex. carbon monoxide (CO), nitrogen oxides (NOx), sulfur dioxide (SO2)
- Volatile organic compounds (VOCs) which can come from paints, solvents, aerosols etc
Indoor sources of combustion gases include, among others, tobacco smoke and combustion appliances; sources of VOCs are tobacco smoke, construction materials, paints, solvents, deodorizers, cleaning chemicals and such like.
Gaseous pollutants range from 0.0003 to 0.005 microns in size.
Have a look at the graph below:
Particles larger than 2.5 microns are mostly lodged in the upper respiratory tract and the nose & mouth area. In comparison, particles smaller than 2.5 microns, as well as gaseous pollutants usually get lodged deep into the lungs.
While particles larger than 10 microns in size can be expelled from the nose and throat by coughing, sneezing or swallowing, this is not the case for particles smaller than 2.5 microns and gaseous pollutants.
We can now imagine that the smaller the air pollutants are in size, the smaller is the chance for our bodies to get rid them completely, and the bigger is the risk to our health.
For example, if gaseous pollutants can enter the blood stream, we will have much more trouble trying to neutralize their negative health-related effects than if we’d managed to “filter them out” at the stage of their entering our bodies.
So we would expect the best home air cleaners to remove as much air pollution from our surroundings as possible – and that includes both particles and gaseous pollutants.
IQAir Home Air Cleaner
© Copyright IQAir
If you do a little bit of research you will find many different types of home air cleaners utilizing different types of technologies (or some combinations of these) to purify the air in your house.Most of them will attempt to remove only certain sizes of particulate pollution. But, like I said above, the best ones will be able to filter out the most dangerous gaseous pollutants as well.
Common Types of Air Purification Technology
So, what technologies do home air cleaners use to improve our indoor environment?
There are several established types of air cleaning technology which are usually designed to remove a specific type of air pollutant (ex., particles up to a certain size).
It is also quite common for manufacturers of high quality air cleaners to use several technologies together (“hybrids”) to fight against several types of pollutants at the same time in order to achieve the best results possible.
Below we discuss the most common types of air purification technology.
Removal of Particles
HEPA stands for high efficiency particulate arresting and is a type of filter that can remove large amounts of very small particles from your indoor air.
HEPA filters are required to capture at least 99.97% of airborne particles 0.3 microns in size.
HEPA filters are not designed to remove gaseous pollutants.
These filters are usually made of very fine glass fibers with a texture similar to blotter paper, and are folded into pleats for greater surface area. They work like a sieve and trap tiny particles inside their fibers.
HEPA is perhaps the most established, proven technology for air purification. It was originally developed in the 1940s and has been successfully used for many decades since then.
Please note that filters that satisfy the efficiency standards mentioned above may also be referred to as “true HEPA” or “absolute HEPA”.
The filters that do not satisfy these standards are sometimes called “HEPA type” or “HEPA like”. They are a lot less efficient than true HEPA filters and are generally not recommended, especially for medical purposes.
|Highly efficient at removing particles up to 0.3 microns in size||Does not remove gaseous pollutants|
|Proven technology that has been in use for many years||Requires frequent replacement of expensive filters|
Electrostatic precipitators can remove fine particles up to 0.01 micron in size. But, just like HEPA filters, they do not remove gaseous pollutants.
Electrostatic precipitators are a type of electronic home air cleaners which use a so called electrostatic attraction to trap charged particles.
Each electrostatic precipitator has two sections: an ionization section where particles from the passing air get electrically charged, and a collector section where the charged particles accumulate on oppositely charged flat plates.
There are several issues with electrostatic precipitators that need to be taken into account before making a purchase.
First, in order to be effective their collector plates require very frequent cleaning.
Second, they produce ozone as a by-product, which is a lung irritant.
Third, they do not remove gaseous pollutants which, as we have seen above, play a big role in causing all sorts of health-related issues.
|Can remove particles up to 0.01 microns in size||Requires very frequent cleaning of collector plates|
|Does not require replacement of expensive filters like HEPA||Produces ozone as a by-product|
|Energy efficient operation||Does not remove gaseous pollutants|
Blueair purifiers are a good example of air cleaners which use electrostatic precipitation. They use it in combination with HEPA technology.
Air ionizers, like electrostatic precipitators, are another type of electronic air cleaners.
But unlike ESPs, they don’t have collecting plates.
Ionizers work by dispersing charged ions into the air. The ions then attach themselves to particles and force them down on to surrounding surfaces such as walls and furniture.
Originally, air ionizers were designed to exclusively produce negative air ions which are believed to have great beneficial effects for human health. (I personally do believe that negative ions have a positive impact on people’s well-being).
Later on though, there came a ban for ionizer manufacturers to make health-related claims of their products, and they were forced to present ionization technology as another air purification solution.
There are several issues that need to be considered before using this technology.
First, it does not really remove particles from your house but gets them attached to other surfaces – these surfaces will get dirty and will then need to be cleaned.
Second, most ionizers emit ozone as a by-product, which is a lung irritant.
Third, they do not attempt to remove gaseous air pollutants but only particles.
|Does not require replacement of expensive filters like HEPA||Does not completely remove particles but gets them attached to other surfaces|
|Quiet & energy efficient operation||Produces ozone as a by-product|
|Does not remove gaseous pollutants|
Removal of Gaseous Pollutants
As we have seen above, the particle removal technologies are not capable of eliminating gaseous pollutants.
But there are two methods which are specifically used to deal with these tiny air pollutants – adsorption and chemisorption. They are especially good at removing a group of pollutants called volatile organic compounds (VOCs).
Activated carbon is also widely used in home water filters for cleaner, healthier tap water.
Adsorption is the process by which gaseous pollutants get physically attached to a surface area. The bigger the surface area, the higher the rate of adsorption.
Activated carbon is the most common adsorbent used in home air cleaners. Other adsorbents include silica gel, activated alumina and zeolites.
Home air purifiers using carbon-based adsorbents must operate in dry conditions, and adsorbents should be changed regularly to keep their efficiency.
Chemisorption takes place when gas molecules chemically react with sorbent material or agents impregnated into the sorbent. The end result are the chemical compounds which are attached to the sorbent as salts, or are broken down and released as carbon dioxide or water vapor or some other elements.
For example, activated alumina is a commonly used sorbent which is often impregnated with potassium permanganate.
Air Cleaners / Air Purifiers Using Adsorption & Chemisorption
IQAir HealthPro Plus
One prominent example of air cleaners which utilize adsorption & chemisorption techniques (alongside HEPA technology) are IQAir air purifiers.
IQAir HealthPro Plus model which is arguably the best home air cleaner on the market, includes a V-5 Cell gas & odor filter.
The V-5 Cell contains 5 pounds of activated carbon & activated alumina impregnated with potassium permanganate which “execute” adsorption and chemisorption inside the unit.
Carbon adsorption eliminates volatile organic compounds (VOCs), and pelletized alumina chemisorption actually destroys harmful chemicals such as formaldehyde.
Gaseous pollutant filters are usually used alongside HEPA filters in home are cleaners.
If you are planning to use a home air purifier to relieve a medical condition, the one with a gaseous pollutant filtration option is highly recommended.
Deactivation and Destruction of Air Pollutants
While the above-discussed methods aim to remove air pollutants from the indoor environment, there are two other techniques – ultra-violet germicidal irradiation (UVGI) and photocatalytic oxidation (PCO) – which aim to deactivate or destroy them instead.
Ultra Violet Germicidal Irradiation (UVGI)
UVGI-enabled home air cleaners reduce populations of airborne biological pollutants, such as bacteria, viruses and molds, inside your house. In other words, UV air cleaners deactivate biological pollutants but do not destroy them completely.
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The effectiveness of UV technology in removing biological pollutants is still under question.
The success rate depends on several factors including UV irradiation dose and system design. For example, the higher the irradiation dose, the higher the rate of pollutants’ reduction.
There are also issues with the fact that air is best irradiated when it is still rather than moving, and it can be quite hard to achieve this in an air purifier with continuously circulating air.
Ozone emitted as a by-product is another concern with this technology.
Maintenance requirements are cleaning the UV lamps and their regular replacements.
UVGI technology is usually used alongside particle filters in home air cleaners.
Photocatalytic Oxidation (PCO)
PCO is an emerging and promising technology.
PCO home air cleaners aim to destroy tiny gaseous pollutants by converting them into harmless substances.
Here is how the photo-catalytic oxidation process works.
- A UV lamp irradiates a photocatalyst (usually titanium dioxide) with strong UV light
- This creates a photochemical reaction and produces hydroxyl radicals
- Hydroxyl radicals oxidize gaseous pollutants which have been absorbed on the catalyst surface
- This process transforms organic pollutants into carbon dioxide and water
The major benefits of PCO are:
- It attempts to destroy the pollutants completely
- It does not have any filters which would require regular replacements (like HEPA filters)
- It does not have any collector plates which would require regular cleaning (like in electrostatic devices)
It does require regular replacement of UV lamps.
It is a relatively new technology and therefore many issues have not yet been completely understood.
Ozone may be emitted as a by-product.
Its effectiveness is still under question.
The operation of this technology may require high energy consumption.
In general, it can be more expensive to operate PCO technology than activated carbon technology (which also deals with gaseous pollutants).
How To Choose A Home Air Cleaner
The number of different brands and models of home air cleaners currently present on the market is staggering.
Some of them offer a pretty basic level of air purification while premium home air purifiers combine the best technologies to produce the best results.
Of course it is fantastic to have such choice.
But at the same time, as consumers we may feel inundated with all this information, and making the right choice may look like a really difficult task.
A good point to start is to understand why exactly you want to buy an air cleaner.
Many users of air purifiers have some sort of allergies caused by indoor air pollutants.
If you are one of them and are on the market for an air purifier, it is almost a must to get a high-quality device which can deal with as many indoor air pollutants as possible.
If, on the other hand, you are just looking to keep air in your house clean and pleasant, getting a device that offers a certain level of particulate pollution removal may be enough.
Home Air Cleaners for Allergy Relief
Our indoor air contains a whole cocktail of large and small pollutants which undermine our immune systems and cause all sorts of allergies.
© Anyunoff | Dreamstime.com<
While particulate pollutants may be easier to catch, tiny gaseous pollutants have proven harder to deal with – they present the highest risk to human health because they can get absorbed into our blood streams.
The best home air cleaners combine at least two types of filtration mechanisms – the one that removes particles from the air and the one that deals with gaseous pollutants.
The best purifiers will have many stages of filtration including pre-filters, true HEPA filters and activated carbon filters.
They are also among the most expensive ones on the market, and that is understandable because they produce much better results than their cheaper competitors.
While the traditional combination of HEPA filters with carbon activated ones has been successfully used for many years, some newer technologies may also turn out to be helpful in relieving allergies.
I have also heard that some people use cheaper home air cleaners for clearing the air of larger particles first and then letting more expensive models finish off the work by removing both smaller particles and gaseous pollutants.
This can save higher-quality air purifiers from having to do the job that cheaper models can do instead. This will also generate monetary savings for the owner in the long-term.
Of course, no one can guarantee that your health will improve once you start using such an air cleaner.
In fact, you should be cautious about any health-related claims made by air purifier manufacturers, as most likely none of such claims would have been approved by any governmental authority.
But air cleaners are certainly there for you to use in combination with other health-strengthening measures that you might want to implement to relieve your symptoms.
There are several well established companies that manufacture air purifiers of highest, medical grade quality.
Their premium devices are widely sold in specialty allergy shops. And you really can’t go wrong with long-term allergy sufferers – these people truly know which air cleaner models work and which don’t.
We are covering some of the best room air purifiers (fighting multiple types of air pollutants) elsewhere on this site as well.
Home Air Cleaners for General Housekeeping Purposes
If you just want to have a generally clean indoor environment and are looking for a basic level of air purification, then cheaper models offering the removal of particulate pollutants may do the job.
But how do you choose one? There is such a multitude of choice in this pure-particle-filtration segment of the market that it is quite easy to get lost.
The Association of Home Appliance Manufacturers (AHAM) has developed a method for measuring an air purifier’s performance called Clean Air Delivery Rate (CADR), to provide consumers with a metric to compare different models of air purifiers.
What is CADR Rating
CADR is the volume of filtered air produced by an air cleaner, measured in cubic feet per minute.
CADR takes into account an air cleaner’s ability to remove only particulate air pollutants completely disregarding gaseous pollutants.
The particles measured by CADR are dust, pollen and tobacco smoke 0.1 to 11 micron in size. The maximum CADR ratings awarded by this system will be 450 for pollen and tobacco smoke and 400 for dust.
The rule of thumb is the higher the CADR rating, the better.
Please remember: you cannot use the CADR metric to compare home air cleaners which remove both particles and gaseous pollutants at the same time – CADR is only capable of testing particulate pollution filtration.
It is almost certain that this rating will not help allergy sufferers to make the right buying decision.
This system has been recognized by US government bodies such as the Environmental Protection Agency (EPA) and the Federal Trade Commission (FTC).
However, it has been widely criticized by experts and consumers alike.
For a number of different reasons.
- AHAM excludes the removal of gaseous pollutants and odors from their tests. We know the dangers posed to human health by gaseous pollutants. While ignoring this parameter the CADR rating does not really help identify the highest-quality home air purifiers which attempt to deal with this type of contaminant.
- AHAM’s tests exclude particles smaller than 0.1 microns in size. We know that the smaller the particles, the bigger the damage to the body. Exclusion of smaller particles works against higher-quality home air cleaners which attempt to deal with this issue.
- AHAM’s tests are very short. The CADR rating system disadvantages the long-term performance of high quality air cleaners by emphasizing the short-term results instead. AHAM’s tests last for only 72 hours which is not enough to assess the real long-term value of an air cleaner.
Indeed, many manufacturers of excellent, medical grade home air purifiers have not signed up with the CADR rating system.
Our advice for consumers is to use CADR as a rough guide when choosing a pure-particle-filtration air cleaner.
We discuss CADR ratings in more detail here.
Other general tips when shopping for any air purifier:
- Go for an established company (or a specialty retailer) that has a proven track record and good after sales support
- Check how many years a warranty is for – the longer the better
- Check how expensive replacement filters are
- Check how easy it is to get replacement parts
- Obsolete (although cheap) models may not have after sale support readily available
- Obsolete models may not have parts easily available for sale
- Do thorough research before making the final decision – it’s well worth your time and effort
Also, please feel free to read an excellent article by our guest air purifier experts about how to choose an air purifier here.
Do Home Air Cleaners Really Work?
They do, especially the best ones which offer a two-stage filtration for both particles and gases.
But please bear in mind that the first steps always recommended for keeping your indoor air clean are source removal and ventilation.
For example, if you keep smoking in the same room where your air purifier works and hope to keep the air clean at the same time, it will be hard to achieve the best results.
If the source (i.e. your tobacco smoke) is always there, your home air cleaner will have to work much harder, its filters will get clogged much faster and you will need to replace them much more often.
Ventilation helps once the sources of air pollution have been eliminated.
Only then should home air cleaners be allowed to finish off the job of your indoor air purification.