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COVID-19 showed the importance of personal protective infection control measures.  The airborne disease called attention to the use of in-room air cleaning technologies like air purifiers.

The in-room pollutants and dust particles are not visible to the naked eye.  Yet, poor air quality can lead to respiratory problems, illnesses, and allergies.  As a preventative method, you can use an air purifier to remove dust, pollen, mold spores, and other irritating small particles from your air. 

There are many decent air purifiers, though only a few great air purifiers. Among these, each model has its unique pros and cons. Your selection should be tailored to your own needs and desires.

Do air purifiers work? What problems they can and cannot solve? How do air purifiers and HEPA filters work? Does an ionizer make sense for your home? We prepared this guide to give you a comprehensive understanding of what air purifiers do, what types there are, how they can be best used, what to pay attention to when buying one, which models we recommend and why.

Overview

Do Air Purifiers Work?

Indoor air can be improved by removing the pollutant sources and ventilating with clean outdoor air.  Air purifiers, also known as air cleaners or air sanitizers, can greatly help this process.  Their abilities, however, are limited.

We have conducted tests with a number of air purifiers we were able to get our hands on.  In addition, we went through many studies on air purifiers.  Below, we dive deeper into these abilities and limitations.

What Does an Air Purifier Do?

Air purifiers proved to be efficient at filtering;

  • Smoke
  • Dust
  • Pollen
  • Mold Spores
  • Allergens floating in the air
  • Particulate Matter from the air.

What does this mean in regard to your health?

Numerous studies ¹ analyzed the cardiovascular effects of the decrease in these particulate matters. Many concluded improved cardiovascular health among the sample population.  The use of in-house air cleaners also reduced ² allergies and asthma symptoms. ³

Due to the number of variables in the test however, there is still no definitive link between the use of air purifiers and health benefits.  These variables include test locations, use of ventilation, vacuum cleaners, pillow covers, the presence of pets, etc.

What Does an Air Purifier NOT Do?

Although air purifiers are successful at filtering allergens, they only remove those that are floating in the air.  Heavier and larger mold spores, pollen, dust mites and other allergens quickly land on the ground or on furniture.  Air purifiers are not able to grab them.

What Does an Air Purifier MAYBE Do?

According to the US Environmental Protection Agency (EPA), it is not clear if air purifiers are efficient at undertaking dangerous gases such as radon.  The effect of air purifiers with ionizers are also in the same ambiguous category in terms of usefulness.

With that, let’s take a look at the different types of air purifiers currently available.

Types of Air Purifiers

Air purifiers use a variety of different technologies in improving indoor air quality.  Some are better than others, and some are straight-up dangerous for your health.  These types include;

Electrostatic

Electrostatic air purifiers use electricity to charge collection plates, to which particles will stick.  It is a rather outdated technology.  These units typically have small and weak fans, if any at all.  Thus, they are ineffective at circulating air.  The maintenance is also a hassle as the collection plates need to be regularly cleaned.

Electrostatic air purifiers alone are inefficient in removing prevalent toxins and allergens in high enough levels to make a significant effect on your health.  However, combining this method with other filtration methods can increase the level of efficiency.


¹ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4515693/

² https://ww2.arb.ca.gov/sites/default/files/classic//research/apr/past/11-324.pdf

³ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3165134/

Ionizer

Ionizers charge ions in the air, which then bond with other particles making them heavier.  The bonded particles no longer float in the air as they land on the floor or on furniture.  These charged particles can also cling on to each other, leading these larger and heavier particles to get trapped by filters more easily.  Ionizers are also useful to use against odors.  These abilities make ionizers a popular technology to be applied within air purifiers.

True HEPA Filter

High-efficiency particulate air (HEPA) filters are certified by the US Department of Energy to remove 99.97% of particles with diameters larger than 0.3 micron.  To give you a benchmark, an average human hair is about 75 microns across.  These filters have repeatedly been tested to be effective at filtering significant amounts of small particles from the air.  The dense lining of fine fibers within these filters enable them to tackle dust, pollen, and mold spores, although they cannot undertake gases or odors.

It is important to note that some manufacturer models that do not feature true HEPA filter, label their products with “HEPA-Like” or “HEPA-Type” in order to capitalize on the positive associations of the technology.

True HEPA filters come at a price as they need replacing once or twice every year and may range from $50 to $200 in some extreme cases

Activated Carbon Filters

Activated carbon, also known as activated charcoal, is a form of processed carbon.  These filters are ideal for absorbing odor-causing molecules and removing toxic chemical gases from the air.  However, they are not able to tackle nitrogen oxide or ammonia.

Activated carbons useful if you suffer from kitchen, smoke, or pet odor or from chemical gasses in a new home.  They are not useful if your concerns are particles instead.

 

Many air purifiers include both activated carbon filters and mechanical filters like HEPA filters together.   Activated carbon gets saturated quicker than pleated filters, so they need to be frequently replaced; typically four times a year.  Each can cost around $50. 

Ozone Generators

Ozone generating machines produce ozone, a toxic molecule that can react with a number of pollutants in order to change their composition.  In the US, ozone is officially recognized as a lung irritant and thus ozone generators may cause risk to the inhabitants when used indoors.  Accordingly, we do not recommend ozone generators.

Vendors of ozone generators that are sold as air cleaners may issue statement and distribute marketing material leading people to believe these devices are safe and useful in controlling in-room air quality.  Health professionals strongly disagree, so please be careful and make sure you do the necessary research while assessing them. This EPA article is a good point of reference.

Ultraviolet Germicidal Irradiation (UVGI)

Ultraviolet light (UV) is used to eradicate bacteria, germs, and viruses by altering their DNA structure at the microorganism level.  It can kill organisms like viruses as they pass through the air purifier or kill the organisms like fungi and bacteria that are already enclosed within the filter in order to prevent them from being multiplied and spread again within your home.

It should be noted that the UV light needs to be quite powerful and its exposure needs to be sustainable in order for the above feature to be effective.  Even then, some mold spores and bacteria are resistant to this sort of radiation.  It is thus arguable if the UVGI is effective or not in most air purifiers that bear the function. 

Air Washer

As the name suggests, air washers are designed to improve the air quality in your home by filtering the air with the use of water.  They also serve as humidifiers.  The air that moves through the washer is scrubbed and the humidity level is adjusted to keep the air consistent.  These devices can only perform a rough cleaning from dust, pollen, and hair.

Indoor Air Quality : Your Needs

Fine Dust

The stereotypical dirt in air are exhaust gases from cars, which are practically full of fine dust.  ‘Dust’ refers to a wide range of solid particles of different sizes.  ‘Fine dust’ refers to particles between 0.5 µm to 50 µm in size.  Particles that are 50 µm or larger are referred to as ‘coarse dust’ instead.

Dust in the house include, but are not limited to dander, hair, animal dander, and also mite drops.  In only a teaspoon of dust, a quarter million drops can be found.

Majority of the dust outside is caused by motor vehicle traffic. On the other hand, dust in homes can commonly be caused by outside air coming in, dead skin, food debris, insects, lead, pets, etc. In addition to these, dust in offices can also be caused by printers and copying devices.

These small ‘fine dust’ particles are not visible to the naked eye, and they can move around very easily.  Thus, they can also move through the respiratory airways and cause diseases or allergies in people.  Runny nose, red eyes, and sneezes are among the common symptoms.  Asthma symptoms are triggered by high level of dust in the indoor air.

Micro-Organisms : Bacteria, Viruses, and Mold

Bacteria and viruses commonly move around in the air.  Sizes of bacteria range between 0.1 µm and 40 µm.  Sizes of viruses are much smaller, they range between 0.01 µm and 0.05 µm.  Mold spores range from 2 µm to 100 µm in size.

Inhaling bacteria or viruses can lead to infectious diseases such as the flu, common cold, pneumonia, bronchitis, diphtheria, meningitis, COVID-19, or other infections. Even the killed germs can cause irritation and inflammation of the respiratory tract. On the other hand, mold spores can cause frontal and sinus infections and trigger allergies.

Typically, the most susceptible to these viral and bacterial risks are the young, the elderly and those with compromised immune systems.  According to a recent study, about 8% of the U.S. population gets sick from the flu each season, leading to the death of 12.000 to 61.000 victims. Common hygiene practices such as washing hands with soap, covering your mouth when coughing or sneezing, and disinfecting most used areas are all essential preventative measures.

HEPA filters are certified to filter 99.97% of all particles larger than 0.3 microns and Most common bacteria and mold spores are larger than 0.3 microns.  Contrarily, viruses are much smaller and may not be trapped by HEPA filters efficiently.  Ultraviolet Germicidal Irradiation (UVGI) and Photo-Catalytic Oxidation (PCO) filtration may help grab viruses more effectively.

Volatile Organic Compounds (VOC)

¨Volatile¨ means that these organic compounds can evaporate at room temperature and thus exist in gas form in the air.  A high proportion of volatile organic compounds (VOC) can also cause poor air quality.

The largest cause of VOC are traffic and heavy industries.  However, these gases can also be released in your home when solvents such as those in cleaning products, paints, and varnishes evaporate.  It is highly probable in newly constructed or renovated structures.

Although not all VOC are harmful, some can be irritating in terms of smell.  In certain cases, they may also cause danger when reacting to ground-level ozone.

Ion Concentration

Ions are electrically charged particles.  The concentration of ions in the air is a determinant in the quality of the air.  It is typically low in dense metropolitan areas.

As the ions are reactive, they can break up molecules, causing unpleasant odors.  On the flip side, ions assure that several charged particles are attracted towards each other, forming larger particles, and thus falling down to surfaces.

Allergies : Pollen, Hay Fever

Allergies are more common than ever.  Allergic rhinitis affects between 10% and 30% of the worldwide population.  Furthermore, 40% of the world has sensitization to foreign proteins in the environment.  Most common airborne allergens include pet dander, mold spores, pollen, dust mite, fine dust, and cockroach allergens.

These typically range from 0.1 microns all the way up to 40 microns.  Larger particles either fall down on surfaces or settle out.  However, they resurface with movement around them.  Sub-micron particles already tend to stay in the air for long periods. You are prone to inhale or contact these particles through your nose, eyes, or mouth.

Most air purifiers are successful at eliminating a good portion of these allergens.  HEPA filters are effective at filtering out 99.97% of the particles larger than 0.3 micron in size.  As for the smaller particles, UVGI and PCO technologies are available.

Asthma

Asthma is caused by allergens or irritants that are inhaled.  These cause airways to swell.  This leads to narrowing of the airways that carry air from the mouth and nose to the lungs.  Symptoms include difficulty in breathing, coughing, and tightness in the chest.  In severe cases, this can be fatal.

According to Global Asthma Network, close to 350 million people have asthma worldwide.  25 million Americans have asthma. Although there is no cure for it, proper treatment and prevention of asthma attacks make it manageable.  HEPA air cleaners appear to be effective at reducing asthma morbidity.

Odors

Many sources can cause unwanted odors at your home.  Some of these include cooking, pets, mold, and smoke.  The best method to eliminate the odors is to minimize or clean up the sources.

Tips

  • Cooking odors can be managed with the use of stove fans and range hoods.  Trash bins and compost bins should be covered all the time and taken out regularly.
  • Pets odors can mostly be avoided if the animals are washed frequently.  It is also important to regularly vacuum the floors and clean the furniture.  You can use deodorizing chemicals to absorb the smell of urine or poo from carpeting.

Mold and mildews need a dehumidifier to control.  Lack of humidity creates an inhabitable environment for their growth and leads the existing spores to die off.  Eventually the mold and mildew odors fade out.

Smoke odors can be caused by cigarettes, cannabis, wood fires or other sources.  It is essential not to smoke indoors to prevent the prevalent odor.

In addition to fighting these odors at the source, some air purifiers are helpful in eliminating unwanted odors.  Use of activated carbon will allow air cleaners to absorb many of the gaseous compounds responsible for these smells.

Pets and Animals

Pets make great companions.  That’s why almost 70% of the US households have a pet at home. Although there are many advantages to owning a pet, animals can have a negative effect on the air quality of your home.  They can introduce airborne irritants, trigger allergy symptoms, leave hair and dander, and have “accidents” leaving unwanted particles on your carpets, floor, and furniture.

Air purifiers can help alleviate these negative effects of owning a pet.

Protection of a Baby in Nursery

As a parent, you are most likely prepared to do everything possible to protect your children.  However, many parents are not aware of the health hazards of poor indoor air quality on babies and children.  Babies are extra susceptible to bad air quality due to their vulnerable immune systems.

For the first two years, babies spend most of their time in their rooms.  Exposure to contaminants in the air may lead to health issues such as headaches, dizziness, asthma, and irritation in the nose, eyes, throat.

Fortunately, there are preventative actions for parents to take on this matter.  Placing air cleaners in nurseries are among these precautions.

Multiple Chemical Sensitivities (MCS)

Multiple Chemical Sensitivities (MCS), also referred to as ‘sick building syndrome’, is a medical condition.  It is characterized by chronic symptoms when exposed to low levels of commonly used chemicals.  These typically include chemicals used in perfumes, pesticides, cigarettes, air fresheners, paint, cleaning and laundry products, and building materials.

MCS can have relation to imbalances in immune, nervous, and hormonal systems.  A person with MCS may react to pollen, dust, mold and animals.  Symptoms are not specific, but they include headaches, nausea, diarrhea, fatigue, dizziness, muscle pain, breathing difficulty, and seizures.  Their intensity may range from mild all the way to fatal.  Air purifiers may filter some of the triggers that lead to MSC symptoms.

Air Purification Process: How Do Air Purifiers Work?

There are several methods to filter particles from the air.  These methods differ in terms of effectiveness against different types of particles, depending on their size and nature.  Some of these methods are also effective against viruses and bacteria.

Many air purifiers use multiple filtering methods and technologies within one device in order to increase overall effectiveness.  This basically means placing multiple filter types within one air purifier.  So, an air purifier may use one or more of the below filters and technologies in order to clean the air.

Prefilter

Pre-filters are protective filters designed to capture large dirt particles such as hair, dust, and pollen. Filtering these particles with a pre-filter prevents other filters in the purifier from clogging.  This extends the life of more expensive filters like the HEPA filter.

You should pay attention that the pre-filters are washable.  This way they can be used for extended periods without the need for replacement.

Summary of Uses :

  • Prorective
  • Filter large particles
  • Washable
  • Extends the life of other filters

HEPA Filter

High Efficiency Particulate Air (HEPA) filters are designed to capture fine particles effectively.  A filter must remove 99.97% of all particles larger than 0.3 microns in size in order to be HEPA-certified.  HEPA filters are commonly used in vacuum cleaners and air purifiers.

Most modern HEPA filters are made of interlaced fibers of different thickness that are woven in a variety of directions. As particles pass through this web, they are removed from circulation in the below four ways:

Diffusion: Ultra-small particles move more erratically as opposed to larger particles.  They are likely to hit and stick to the woven fibers.

Impaction: Large contaminants like hair, dust, and pollen travel in a straight path.  They bump into the fiber and stick to it.

Interception: Particles following the flow in the air stream continue on their path and stick to the sides of fibers.

Sieving: Particles that are headed between two fibers get stuck between the gap, as long as the particle is larger than the gap.

Summary of Uses :

  • Filter dust particles
  • Filter allergens
  • Filter pollen and mold spores
  • Filter bacteria
  • Filter cigarette smoke and tobacco smoke

Activated Carbon Filter

Activated carbon filters help trap odors and chemicals in their absorbent pores. Charcoal is treated with oxygen, causing numerous tiny pores to open up between the carbon atoms and activated carbon to be created.  These filters look like scrub brushes and have sponge-like structures.

Various air components such as chlorine compounds and dirt particles stick to the inner surface of this filter.  Harmful ozone can also react with the carbon and become harmless.  Activated carbon filters are generally used for getting rid of odors.  This includes the smell of ozone, cigarette smell, and pet odors.

Summary of Uses :

  • Decomposition of harmful gases
  • Removal of unpleasant smells
  • Capture of organic molecules

Ultraviolet Germicidal Irradiation (UVGI)

Ultraviolet Germicidal Irradiation (UVGI) cleaners intend to improve the air quality by shutting off biological pollutants that are airborne or those that grow in humid HVAC surfaces.  This airstream disinfection application is used to kill microorganisms, germs and bacteria as they pass through the air purifier.  Some mold spores and bacteria however, are resistant to UV radiation.

The effectiveness of UVGI cleaners depends on the UV exposure.  However they are better used as an additional method to conventional particle filtration systems, as opposed to being used alone.

Summary of Uses :

  • Captures bacteria and gases broken down by UV light
  • Regenerates by itself
  • Low maintenance

Photocatalytic Oxidation (PCO)

Photocatalytic Oxidation (PCO) cleaners destroy gaseous pollutants, as well as their odors, by converting them into harmless structures.  PCO cleaners use a UV lamp and a photocatalyst in order to produce hydroxyl radicals.  These hydroxyl radicals then attack certain organic substances.

Summary of Uses :

  • Traps gaseous pollutants and the smells
  • Low maintenance

Air Washer

The air is perceived to be fresh and cleaner after a heavy rain shower.  Air washers mimic the same effect by passing air through mist.  The fog of liquid captures large particles, dust, and water-soluble particles, leading to clean and humidified air flowing out.  The humid air is useful to avoid respiratory diseases and pleasant to inhale.

Summary of Uses :

  • 2-in-1 appliance : air purifier and humidifier
  • Removes water-soluble particles from air
  • Captures large particles and pollens

Thermodynamic sterilization (TSS)

Thermodynamic sterilization (TSS) is another technology used in air cleaners.  TSS uses a ceramic core, which is heated up to 392°F (200°C).  The air passes through the heated ceramic core by the process of air convection.  Bacteria, viruses, and mold spores cannot survive at this temperature, so clean air flows out.

TSS technology does not require any fans or blowers as the heated air inside the device rises, drawing fresh air out of the device.  This allows thermal air purifiers to be almost completely silent.

Summary of Uses :

  • Reduces concentration of ozone
  • Kills germs, viruses and mold spores through heat

Ionizer

Ionizers electrically charge air particles and increase the ion concentration in the air.  Charged particles are more reactive and they are able to get rid of particulates, microbes, and odors.  Charged particles also attract each other, causing the larger united particles.  This makes them large enough to get easily filtered or heavy enough to fall on to the ground or surfaces.  They can easily be dusted or wiped off.

Ionizers are able to remove certain bacteria, dust, mold, pollen, as well as cigarette smoke, and other unwanted odors.  They help alleviate the impact on people suffering from seasonal allergies or hay fever.

It is important to point out that some small ionizers are too weak to have any noticeable effect.  However larger ionizers put a greater number of ions in the air, which causes ozone to be generated.  Although ozone is excellent in splitting larger pollutants and combatting odors, it can be harmful to humans.  It is best to avoid the use of ionizers when you are present in the room.

Summary of Uses :

  • Electrically charged air particles neutralize odors
  • Ions in large numbers may generate ozone, which may be harmful