How do air purifiers work?

Did you know that indoor air is often more polluted than the air outdoors? The Environmental Protection Agency (EPA) has found that human exposure to air pollutants indoors may commonly be two to five times higher than outdoor levels of pollution

Pollutants such as dust, pet dander, pollen, mould, fungus, bacteria, and viruses can contribute to poor air quality. Poor air quality can lead to short-term health effects such as coughing, eye irritation, and headaches. It’s also possible for poor air quality to create and contribute to long-term harmful health effects such as asthma and other respiratory condition. It can even affect the cardiovascular system. 

So, what’s the best way of ensuring the air in your home is as healthy and clean as it can be? 

An air purifier is a machine with an air filter that works to remove fine particles and gaseous pollutants from your indoor atmosphere to clean the air and create a healthier environment.

There are different types of air purification devices. However, they generally work on similar principles, using scientific and mechanical processes to remove airborne particles from an indoor environment to create better air quality. 

There are many different types of air filters, all with their own strengths and techniques. The right one for you depends on what type of pollutants and particles you want to remove from the environment. 

It’s worth doing your research to make sure that the model you purchase is appropriate for the task. Don't purchase a filter that can only remove larger particles from your environment when you want to remove fine dust particles.

What are the basic functions of an air purifier?

Air purification devices generally comprise a motor, fan, and air filter. The motor and the fan operate to circulate the air, while the filter works to remove pollutants from the air as the air passes through the machine. In addition, some air filters use negative ion generators to attract airborne particles and successfully remove them from the atmosphere. 

What are the techniques used in air filtration?

There are multiple techniques used to filter and deliver purified air. The following are the most popular methods:

Mechanical filtration with a fibrous medium

The most widely used technique for air purification, mechanical filtration systems remove airborne particle pollutants such as dust, dust mites, and pollen from the air by trapping them in a fibrous filter for removal. Mechanical air filters encompass any type of dry media filter, including the disposable air filters often used by HVAC systems and HEPA devices.

Mechanical filters operate using two principles. In primary air filtration, the dust attaches to the filter. The secondary process is removing particles from the filter medium. As dust builds up on the filter material, filters become less efficient, so it’s vital to maintain clean filters for optimum pollutant removal. 

HEPA filters, or high efficiency particulate air filters, are the most efficient type of mechanical air filters and should remove at least 99.95% of airborne particles from the environment.

Electrostatic precipitation

These filters work using the process of electromagnetism, passing polluted air through an ionisation section to draw out airborne pollutants and trap them for removal. They work using a similar principle to magnets. As positive and negative charges attract each other, this process adds an electrical charge to particles, which are then trapped and stored on an oppositely charged flat plate for disposal. In the case of electrostatic air filters, there is no filter medium as charged plates are used instead.

Electrostatic air filters are efficient at trapping both large and fine particles. If you’re looking to remove fine pollutants, this may be the most efficient filter as the fine particles receive enough electrostatic charge to be collected on the plates. These fine particles may be missed by other types of filters. 

Electrostatic air cleaners do not use the MERV (minimum efficiency reporting value) scale as they are not classed as mechanical air filters. Instead, they are measured on an arrestance (ability to remove synthetic dust) scale, with most filters scoring a rating of 99.95% plus. 

It’s important to note that arrestance is not the same as efficiency. It simply measures the percentage of weight, in grams of dust, that a filter can hold before it becomes loaded.


Not all airborne pollutants are particles. There are also gaseous pollutants such as molecules generated from combustion processes, including gas cooking stoves, vehicle exhausts and tobacco smoke. Air may also contain volatile organic compounds (VOCs) such as cleaning fluids, adhesives, paints and varnishes. These molecules require a specialist air filter that’s designed to remove gaseous pollutants.

Adsorption is an exothermic (heat releasing) process that uses a material with a high internal surface area, a suitable pore structure, and surface chemistry to remove gaseous molecules from the air. Activated carbon is the most common substance used in air filtration. 

However, it’s important to note that this process does not remove airborne particles; it simply reduces the levels of gas and odours. As a result, filters using an adsorber system are usually combined with other methods of filtration to provide clear air and prevent the carbon or other media from being overloaded with dust.


Photocatalysis is another method of removing gaseous pollutants. Instead of using adsorption media, photocatalytic air purifiers use UV light and a catalyst – usually titanium dioxide – to purify the air. 

This process operates using UV light to energise the catalyst, which then targets the harmful pollutants and effectively destroys them. While this may seem like a cleaner and safer method than one which traps pollutants for later disposal, photocatalytic air purifiers can create trace amounts of ozone, which is a toxic air pollutant that can inflame and damage lung tissue. 


The plasma method uses a high voltage current to ionise the air and charge airborne molecules. This creates reactive radicals, which then attack and destroy airborne pollutants. 

However, as with photocatalysis, this process creates the potentially harmful by-products of ozone and nitrogen oxides. In addition, ion generators typically only work well when used alongside a different type of air filter, such as a mechanical one, to remove airborne particles.

Should you leave an air purifier on all day?

The air within your home environment is constantly changing. Every time you do something like turn on the stove, use scented products, or even stroke your pet, indoor pollutants are released. These pollutants become a part of your home air, unless you use an air purifier to remove them from your environment.

In addition, if you open a window or a door, you’re also bringing outdoor pollutants into your home. In fact, the chances are that outdoor pollutants are already seeping into your home, as not every entrance point is fully sealed. 
Apart from an efficient ventilation system, the only way to purify your air and remove these pollutants is by using a dedicated air purifier. 

To understand whether you should leave your purifier running at all times, or whether it should be switched off periodically, it’s important to understand what happens when you switch your air purifier off. 

The work of an air purifier doesn’t really stop. Even the most effective range air filters can take hours to fully clean the air inside a room. So, when you switch off your purifier, pollutants will begin to gather again, which in turn, makes it more difficult for the purifier to do its job when it is again switched on. 

It is recommended to leave your air purifier on continuously. This means that not only is the filter working to maintain clean air, it is also removing any new contaminants that may enter your home. 

It can be tempting to turn your air purifier off during the night. It’s easy to assume that because you are sleeping, no new pollutants are being introduced to your home atmosphere. However, that isn’t correct. 

Indoor air pollutants such as pet dander, dust mites, and mould can quickly accumulate while you are sleeping and your air filter is switched off. Without your air filter to purify the air, you may suffer from fitful sleep due to aggravated allergies and asthma symptoms. 

In fact, if you only have the budget to buy one air purifier, we recommend that you place it in the bedroom. We spend around one third of our life sleeping, and the quality of our sleep contributes significantly towards our overall health. By running an air filter in your bedroom, you’re removing harmful pollutants which may hinder your ability to sleep and decrease your sleep quality. 

It’s also worth noting that you should change your air purifier’s filter regularly. A build-up of particles will mean your filter can't work as efficiently which negates most of the positive effects of using an air purifier. Most filter replacements are inexpensive and will ensure your air cleaner can work at high efficiency.

Are air purifiers good for your health?

The answer to this is a resounding yes. Using an air filter indoors can have a huge impact on improving the quality of air in your home environment. This in turn will have a significant impact on your health, with particular benefits for your respiratory system. 

It is vital, however, that you take the time to choose the correct air purifier. Some may have an adverse effect on your health as they produce by-products such as ozone or nitrous oxides.

What are some common home air quality problems?

  • Dust and dust mites
  • Pet dander, hair, and odours
  • Plant or pollen allergies
  • Bad smells from a number of sources, including cleaning fluids and by-products from cooking
  • Sneezing and coughing
  • Itchy skin, sore eyes, and irritated membranes
  • Volatile organic compounds (VOC) from chemicals
  • Asthma attacks

Ultimately the only true solution to eliminating these problems is to remove the source of the air quality problem. Sometimes this isn’t viable, for instance getting rid of a pet is a rather extreme way to remove pet dander from your environment. 
In this case, an air filter is your best option. It doesn’t just alleviate symptoms but works on trapping or removing the airborne pollutants to create a cleaner, healthier environment. 

Air cleaners with HEPA technology filters can remove up to 99.95% of the airborne pollutants from your home environment. 

What are the health benefits of using an air purifier?

One of the main reasons for purchasing an air purifier is to alleviate the symptoms of asthma. With one in 12 adults suffering from asthma, it’s a common condition with a wide range of symptoms, from coughing and wheezing to full-blown asthma attacks. The root cause of asthma is inflamed bronchial tubes. This means that airborne pollutants can further irritate the respiratory system of asthma sufferers and increase the frequency and severity of symptoms. 

Using an air purifier with the ability to remove both small and large pollutants from the atmosphere can significantly make a difference for asthma sufferers and ease their symptoms.

But it’s not just asthma sufferers who can benefit from an air purifier; let’s take a look at some of the further benefits: 

Removal of harmful chemicals from the home environment

The home environment can harbour a range of harmful chemicals. Every time you use cleaning products, they release a variety of toxins such as ammonia, chlorine, and phthalates into your home. In small quantities, these toxic chemicals are relatively harmless, however routine exposure can lead to serious health conditions such as cancer, tumours, or neurological disorders.

In addition, whenever the doors or windows of your home are open, gasses from the outdoors, such as nitrogen dioxide and carbon monoxide, can enter your indoor space. This can be a particular problem if you live in a populated area with high levels of motor vehicle traffic or industrial buildings. Exposure to carbon monoxide and nitrogen dioxide can increase your risk of developing conditions such as dementia or Alzheimer’s.

If you choose an air purifier specifically designed to cleanse the environment of gaseous pollutants, such as an adsorption filter that uses an activated carbon filter, it will remove most of these chemicals from the air and your home's air will be cleaner and fresher. 

Neutralisation of odours in the home

It’s not just harmful chemicals that an air filter can remove from the home, they can also deal with unpleasant odours. The chemical process during which compounds such as gasoline, benzene, and formaldehyde break down can release unpleasant odours into the environment. Known as volatile organic compounds (VOCs), these chemicals can be found in common household items such as paints, varnishes, aerosol sprays, and even air freshener. 
VOCs don't just create an unpleasant odour, these compounds can also cause nausea, headaches and breathlessness. Most of us know that it's a good idea to open a window when a room has been freshly painted. The smell of fresh paint can cause a headache. This is due to the VOCs that paint releases into the atmosphere. 

However, if you open a window, this can also allow the introduction of more outdoor pollutants into the home. 
Using a combination air purifier with a HEPA filter and an activated carbon filter will not only trap harmful gasses and odours, but will also tackle any particles in the air to create better air quality and a healthier environment. 

Improving your sleep quality

Clean air has a huge effect on the quality of your sleep. It is simple to assume that when you are sleeping, air quality has no impact on your health. However, that isn’t the case. Airborne pollutants such as mould, dust, pollen, and pet dander can trigger allergies, hay fever, and asthma that can lead to a disturbed night of coughing, sneezing, itchy skin, and nose congestion. 

The best way to combat this is by using a HEPA air filter in the bedroom. As previously mentioned, we spend up to a third of our lives sleeping, or attempting to sleep, so an air purifier placed in the bedroom can have a huge impact on our lives by reducing drowsy days and restless nights. 

Elimination of harmful pollutants from building materials

Whether you live in a period or modern home, the building materials used to create your house can emit harmful compounds that may damage your long-term health.

The biggest culprit for this is asbestos particles.

Commonly used from the 1940s to the 1960s, asbestos roofing materials and insulation pipes are present in many older buildings. As asbestos ages, it begins to shed dust into the ambient air. These particles, when inhaled, can lead to lung scarring known as asbestosis. Other symptoms, such as swelling in the neck or face, loss of appetite, and difficulty swallowing may also be present. It can also increase the risk of lung cancer. 

Using a HEPA air filter to trap and remove these particles is a safe and efficient method to decrease your chances of harmful effects and improve the air quality. 

Can an air purifier keep me safe from COVID? 

Airborne diseases such as COVID, along with the common cold and flu, are spread via tiny pathogens present in the air. As a result, these conditions are incredibly contagious, particularly when one family member or house inhabitant is unlucky enough to fall ill. 

COVID spreads from an infected person’s mouth or nose. Tiny airborne droplets of liquid are formed when sufferers cough, sneeze, speak or breathe. Because everyone in the environment is sharing the same infected air, it is common for the condition to spread throughout the household. 

A recent study from the University of Cambridge and Cambridge University Hospitals NHS Foundation Trust explored whether portable air filtration devices could be used to reduce airborne SARS-CoV-2 in COVID wards and a COVID Intensive Care Unit. 

As these wards have been repurposed as COVID wards, they are not designed for managing respiratory infections and do not have specialist equipment to do this. Instead, the team used a portable HEPA filter and UV steriliser, and then measured the results. 

Dr Andrew Conway Morris, from the Department of Medicine at the University of Cambridge, said: “We were really surprised by quite how effective air filters were at removing airborne SARS-CoV-2 on the wards. Although it was only a small study, it highlights their potential to improve the safety of wards, particularly in areas not designed for managing highly infectious diseases such as COVID-19.

There is strong evidence to support the efficiency of HEPA filter air purifiers in reducing and in some cases fully removing traces of COVID from the air. When this infection is removed from the air, you are safeguarding yourself and your family members and decreasing the risk of becoming ill. 

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