Choosing an air purifier: the comprehensive guide

Indoor air quality, often overlooked in building regulations that predominantly focus on energy efficiency, has emerged as a key concern for residents in recent years. The Covid-19 pandemic has notably accelerated this shift in focus. The realization that we inhale approximately 12,000 liters of air daily, primarily in enclosed spaces, underscores the importance of air quality.

Consequently, the demand for air purifiers has spiked, leading to a burgeoning market filled with a variety of products. These products, employing diverse technologies, all promise one essential benefit: the provision of clean, healthy air in various settings such as homes, offices, workshops, shops, and waiting areas.

But how does one make an informed choice? What are the pros and cons of the different air purifiers available on the market? Are they universally effective for all environments and pollutants? What factors should be considered when determining your specific needs?

In this guide, we aim to help you navigate these questions by offering a comprehensive overview of the available technologies, their benefits, and their ideal applications.

I - The role of the air purifier
II - The different air purifier technologies
III -TEQOYA air purifier technologies
IV - Comparative summary table
V - Other selection criteria
VI - Sources

I - The role of the air purifier

During the Covid-19 pandemic, a study by the Institut Pasteur revealed that 80% of infections occurred in enclosed, poorly ventilated spaces. This highlighted the importance of air renewal in reducing transmission risks. Air renewal is a crucial step towards better indoor air quality, but it's not a complete solution. While it dilutes indoor pollution, it doesn't eliminate it entirely. Moreover, the incoming air can bring its own pollutants, and heating or cooling this air consumes additional energy.

In commercial buildings with air recirculation systems, there have been concerns about virus transmission through ventilation and climate control systems.

Air purifiers address these issues by cleaning indoor air, either trapping or destroying pollutants. There are various technologies available, such as HEPA filters, activated carbon, photocatalysis, ozonation, plasma, UV-C, ionization, and electrofiltration. Each technology has unique features, and selecting the right air purifier depends on specific needs. Considerations include the intended room for the purifier, the types of pollutants present, the occupants' sensitivities, ease of use and maintenance, and whether the purifier emits any harmful chemicals itself.

II - The various technologies of air purifiers

1. HEPA filter air purifiers: particle filtration
2. Activated carbon air purifiers - molecular filtration
3. Photocatalysis air purifiers
4. Ozonation air purifiers
5. The cold plasma air purifier
6. The ionisation air purifier
7. Electrostatic air purifiers
8. UV-C radiation air purifier

1- HEPA air purifiers: particle filtration

HEPA air purifiers, which make up approximately 80% of the market, employ a filtration system to clean the air. It is typically paired with other filters:

• A pre-filter captures coarse dust particles. This not only prevents rapid clogging of subsequent filters but also extends their lifespan. It's important to note that the greater the filtration capacity, the quicker the filter may clog.
• An activated carbon filter, which works as described below.

Pollutants treated

All particulate pollutants - fine particles, pollen, sand and minerals, ash, dust, smoke - and viruses.

Why choose this air purifier?

Ideal for environments where regular filter changes are feasible and a larger footprint is acceptable, such as:

• Offices
• Classrooms
• Canteens

Maintenance

Pre-filters require replacement every 3 to 6 months, and the HEPA filter annually

Advantages

• Under laboratory conditions, the HEPA filter captures at least 99.97% of particles of all sizes, making it highly effective.
• There's no risk of secondary emissions (like ozone or particles from ozone interacting with VOCs), unlike some active technologies.

Points to consider

• The overall efficiency of an air purifier with a HEPA filter differs from the filter's individual efficiency. A complete unit's filtration rate, considering potential leaks in the filter assembly, ranges from 90% to 99.5%, depending on the appliance's quality. This is crucial as HEPA filters significantly obstruct airflow.
• According to the "Effectiveness of Home Air Cleaners in Reducing Indoor Levels of Particles" study ⁽⁴⁾, a HEPA filter air purifier reduces ultrafine particle pollution by 68%. Hence, it's important to be skeptical of claims of "absolute" filtration, as they don't reflect the actual reduction in indoor pollutants.
• As per the same study, a HEPA filter loses 25% of its efficiency in 6 months in a lightly polluted environment, and even more rapidly in highly polluted settings.
• Maintenance is demanding and costly: Frequent replacement of clogged filters is essential, and handling them can be tricky as pollutants may disperse into the air. This also generates waste and impacts the air purifier's cost and carbon footprint over its lifespan.
• Sources of noise and drafts: To achieve maximum performance, high air speed inside the purifier is necessary, which increases noise levels.
• Choosing and installing the correct model can be complex. The number of filters is a key factor: more filters mean less frequent clogging of HEPA and activated carbon filters, but they can also reduce airflow or increase noise, drafts, and energy consumption. Professional installation advice is often necessary.
• The materials used in HEPA filters, typically type 475 glass microfibers, are classified as carcinogenic. In industrial settings, human exposure to these materials is closely monitored and regulated. They require careful handling and special disposal methods, as these microfibers can be hazardous if released into the air.
• The filters' resistance to airflow increases energy consumption.

More details in our article about HEPA filter air purifiers

2- Activated carbon air purifiers - molecular filtration

Activated carbon filters target chemical pollutants, specifically odors and gases, in indoor air. They operate on the principle of adsorption: the gas molecules are absorbed throughout the highly porous activated carbon when they come into contact with it. Activated carbon filters are often paired with HEPA filters in air purifiers. For more information, see our article on activated carbon filters.

Pollutants treated

Odours and gaseous pollutants, including volatile organic compounds (VOCs), particularly aromatic compounds, NOx, SOx, hydrocarbons, etc.

Why choose this air purifier?

• Industrial sectors
• Homes, especially for asthma sufferers
• Offices
• EPHAD, retirement homes, hospitals

Maintenance

Replace the filter every 6 months.

Advantages

Particularly effective against aromatic VOCs emitted by furniture and interior furnishings, such as glues, varnishes, parquet flooring, wood products, and cleaning agents.

Points to consider

• Its actual efficiency can be challenging to gauge, as it greatly depends on ambient conditions like temperature, humidity, and pollutant concentration.
• Less effective for lighter VOCs, notably formaldehyde.
• Adsorption relies on the balance between the adsorbent material and the ambient air, meaning the material can release trapped gases if the ambient conditions change.
• Consumes energy.
• May contribute slightly to the overall noise of the air purifier.

3- Photocatalytic air purifiers

Photocatalytic air purifiers work by breaking down pollutants through the action of light on a catalyst, typically titanium dioxide (TiO2). Ideally, this process results in the production of mainly water and carbon dioxide. However, current concerns about potential health risks associated with this technology are worth noting. For an in-depth understanding, please refer to our article on photocatalysis.

Pollutants treated

Volatile organic compounds (VOCs), inorganic pollutants, pathogenic microorganisms, viruses and bacteria, odours

Why choose this air purifier?

Suitable for medical and industrial settings, including hospitals, laboratories, and clean rooms.

Maintenance

Requires minimal maintenance

Advantages

Generally has a long service life

Points to consider

• In practice, the photocatalytic reaction can be incomplete, leading to the emission of chemical degradation by-products, such as titanium oxide microparticles, ketones, aldehydes, and organic acids. These secondary pollutants, which can be toxic or irritating, might pose greater health hazards than the original pollutants. Assessing their composition independently from the air treated by the purifier is challenging. It's advisable to first identify the specific pollutants in the environment and ensure they are limited in number. This technique is less suitable for environments with ethanol or methanol-based pollutants.
• Titanium dioxide (TiO₂) is classified by the International Agency for Research on Cancer (IARC) as a Group 2B agent, meaning it is "possibly carcinogenic to humans."
• UV-C radiation, typically used at a wavelength of 254 nm, is invisible but can harm eyes and skin. It emits hydroxyl radicals (OH), which are detrimental to health.
• May produce a slight noise.

4- Ozonation air purifiers

Primarily used in professional settings, ozonation involves generating substantial amounts of ozone (O₃). Ozone is a potent disinfectant, effectively combating both chemical and biological contaminants. However, due to the risks it poses to human health, ozonation is a specialized air and surface treatment process, typically reserved for controlled use in medical and industrial environments.

Pollutants treated

• Odours
• A wide range of gaseous indoor pollutants, including volatile organic compounds (VOCs), alcohols, etc.
• Biological pollutants, such as bacteria

Why choose this air purifier?

Suitable exclusively for use when no people (or animals) are present, particularly for disinfection purposes.

• Chimneys or extraction systems in industrial and food processing plants
• Professional kitchens
• As a mobile solution for hotels, restaurants, sports centres, etc.

Maintenance

Requires minimal maintenance

Advantages

• Easy to install
• No consumables required

Points to consider

The ozonator must operate in unoccupied spaces, as effective ozone concentrations are harmful to health. Ozone can irritate the skin and mucous membranes, leading to respiratory issues, coughing, and asthma. It also reacts with indoor air pollutants to create potentially hazardous secondary pollutants.

• European regulations suggest an average daily exposure target of less than 60 ppb, significantly lower than the concentrations emitted by ozone generators, which need several parts per billion to be effective as disinfectants.
• The World Health Organization (WHO) advises keeping average exposure levels below 20 ppb to prevent adverse health effects.

5- The cold plasma air purifier

Cold plasma technology eradicates organic molecules via oxidation reactions. These reactions are initiated by free radicals generated through ionisation.

Pollutants treated

• Chemical and gaseous pollutants such as volatile organic compounds (VOCs), inorganic pollutants and micro-organisms
• Pollens, odours
• To some extent: biological pollutants and living organisms like some bacteria or viruses.

Why choose this air purifier?

• Industrial plants
• Hospitals
• Offices when integrated into an air handling unit

Maintenance

Maintenance can be delicate and sometimes unreliable due to the high oxidising power of the chemical compounds in plasma.

Advantages

Relatively low power consumption

Points to consider

• High initial cost
• Similar to ozonation and photocatalysis, plasma technology also carries a significant risk of emitting secondary pollutants. In cases of incomplete oxidation of primary pollutants, it may release potentially carcinogenic substances like carbon monoxide, nitrogen oxides, ozone, etc.

6-The ionising air purifier

Ionising air purifiers are major sources of electrons, thereby generating negative ions. Once released, these ions bond with airborne particles, which are usually neutral or positively charged, endowing them with a negative charge. The charged particles then either settle to the ground or are drawn to walls, a process facilitated by the repulsion of similarly charged particles and attraction to surfaces. This effectively removes them from the airstream. TEQOYA air purifiers operate on this principle but unlike many other products on the market, they do not produce ozone.

Another ionisation method involves producing hydroxyl radicals (OH radicals). These radicals remove hydrogen from organic pollutants, such as viruses or bacteria, neutralising their harmful effects.

Pollutants treated

• Biological and chemical pollutants, including viruses
• Dust and fumes
• Odours particularly those from certain gases or tobacco smoke
• Fine particles

Why choose this air purifier?

• Various applications
• More effective in unoccupied rooms

Maintenance

Simple and cost-effective

Advantages

• Negative ions, which are plentiful in nature, purify and refresh the air, contributing to an enhanced sense of well-being.
• Promotes overall well-being and improved cognitive function.
• Low energy consumption.
• Long lifespan.
• No noise disturbance.
• Compact and space-efficient.

Points to consider

Most air ionisers emit ozone. As we saw earlier, this gas is harmful. The more powerful the ionisation, especially to combat VOCs and fine particles, the greater the risk of exposure to ozone and incomplete oxidation products.

7-Electrostatic air purifier

Electrostatic air purification operates in two phases:

• Air particles are charged either negatively or positively in the ionisation zone.
• These charged particles are drawn to and adhere to plates that generate a strong electrostatic field. In industrial systems, particularly, the accumulated dust eventually falls into a collector.

This highly efficient and robust technology, capable of capturing large volumes of particles, is frequently used in filtering industrial combustion emissions. TEQOYA has innovated upon this, developing a patented technology called e-filtration. It harnesses the benefits of electrostatic filtration, also known as electrofiltration, while mitigating its risks and limitations.

Pollutants treated

All types of pollutant particles: urban pollution, viruses, bacteria, allergens, mould, ultrafine particles, dust, smoke, pollen, viruses, odours, and volatile organic compounds (VOCs).

Why choose this air purifier?

• Specific industrial installations: power stations, incinerators, boiler rooms, etc.
• Large kitchens

Maintenance

Filter replacement or plate cleaning required every 3 to 6 months.

Advantages

Points to consider

• Significant maintenance
• Risk of generating ozone
• Noisy

8- UV-C radiation air purifier

These air purifiers use a type C ultraviolet (UV-C) lamp to expose and destroy pollutants. They come in different forms: suspended lamps, which expose the entire volume of a room to the radiation, and models integrated into ventilation systems, which treat only the air and surfaces within the air ducts.

Pollutants treated

All biological pollutants :

• Pollen
• Germs, bacteria and to some extent viruses and Covid-19
• Moulds and fungi

Why choose this air purifier?

• Laboratories, medical practices, nursing homes, retirement homes
• Meeting rooms, waiting rooms, reception areas, restaurants...

Maintenance

• Low maintenance costs
• Lamp replacement, which can be costly, is required every 3 to 5 years.

Advantages

Well-suited for areas with high viral loads or places with frequent population turnover.

Points to consider

• Substantial initial investment for systems integrated into ventilation.
• The most common UV-C wavelength (254 nm) emits harmful radiation to the skin and eyes: direct exposure should be avoided. It's also known to emit hydroxyl radicals (OH), which are air pollutants.
• The less common UV-C wavelength (222 nm) may be safer for human exposure but carries the risk of significant ozone emission.
• High energy consumption and expensive lamp replacement costs.

III - TEQOYA air purifier technologies

TEQOYA air purifiers generate large quantities of negative ions, which are abundantly found in nature, especially in rejuvenating environments like mountains and rivers. These ions naturally purify the air by charging polluting particles, causing them to settle to the ground.

We offer two types of air purifiers. Both are effective against inert particles - such as urban pollution and dust - as well as allergens like dust mites, pollen, and mould, and bio-contaminants including viruses and bacteria.

1-Our ozone-free ionising air purifier

This technology neutralises particles by causing them to leave the air stream once they fall to the ground. The absence of a filtration system means these particles are not trapped, but it also allows the purifier to operate without any sound perceptible to the human ear, making it extremely easy to use and maintain. Special attention has been given to its design. This air purifier is particularly recommended for:

• Home living areas: living rooms, bedrooms, etc.
• Beauty and aesthetics-related professional settings, where it can capture odours from various products and contribute to the overall well-being of the space.
• Small, enclosed areas such as taxis.

Discover TEQOYA's range: the TEQOYA T200 for small rooms, the TEQOYA T450for larger spaces, and the Nomad, specifically designed for use in cars.

2- Our electrofiltration air purifier

This purifier operates on a combination of ionisation technology and an electrofiltration system. The ionised particles are captured in a cleanable filter, making this purifier ideal for environments with higher pollutant concentrations. It features four adjustable speeds, allowing it to be tailored to specific needs and maintain good indoor air quality, regardless of the level of particle emission from human activities.

It is particularly suitable for :

• Home areas with notable odour or smoke issues, like the kitchen.
• Craft activities generating dust (woodworking, plastering, baking, etc.) or odours (restaurants, painting, leatherworking, etc.).
• Spaces with large crowds in confined settings (training and conference rooms, etc.).
• Areas where vulnerable individuals are present (doctor's surgeries, retirement homes, nurseries, schools, etc.).

The noise level of the electrofiltration system increases with the selected setting. The lowest setting, suitable for continuous operation, produces a barely noticeable sound. The higher settings are audible but are typically used:

• When there is significant human activity, and thus more background noise, necessitating enhanced air purification.
• When the room is unoccupied, like breaks in conference rooms or closing times in doctor's surgeries.

The effectiveness of this technology has been recognised by SOLIDEO, selecting our electrofiltration solution for the Athletes' Village accommodation for the 2024 Olympic Games.

Explore our ALANA/ E500 model, designed for saturated environments and professional use.

3- Comparison of TEQOYA air purifiers

Pollutants treated

Both purifiers eliminate up to 99.9% of pollutants, including urban pollution, viruses, bacteria, allergens, mould, ultrafine particles, dust, smoke, pollen, odours, and VOCs.

Why choose this air purifier?

Ozone-free ionisation air purifier:

• Homes: bedrooms, living rooms, offices and other quiet rooms
• Health and beauty professions: beauty salons, hairdressing salons, manicure salons
• Cars

Electrofiltration air purifier:

• Home areas with odours and fumes, like kitchens
• Children's playrooms, bedrooms for people with low noise sensitivity
• Dust-producing industries (woodworking, plastering, baking, etc.) and odour-producing areas (restaurants, etc.)
• Spaces with large audiences (conference rooms)
• Vulnerable people's areas (doctor's surgeries, retirement homes, schools, etc.)

Maintenance

Advantages

• Nature-inspired technology promoting well-being and cognitive activity
• Patented controlled electrostatic discharge technology, minimising ozone and harmful compound emissions
• Energy efficient
• No disposable consumables
• Compact, easy to install, move or fix
• Aesthetic design
• Long service life
• Made in France

Ozone-free ionisation air purifier:

• Inaudible
• No settings, user-friendly

Electrofiltration air purifier:

• Noise level depends on setting.Hardly noticeable at level 1.
• Flexibility of adjustment and possibility of automatic adjustment
• Can be connected to a sensor for automatic control

Areas of improvement

We are committed to continuous improvement, investing over 20% of our turnover in R&D annually. Future projects include:

• A connected sensor for monitoring and controlling air quality
• Enhancing our purifiers' effectiveness against formaldehyde

IV - Comparative summary table

V - Other criteria for choosing an air purifier

Once you have determined that the chosen technology meets your needs, you can consider additional, more subjective criteria. These may vary based on personal preferences for individual buyers or align with a company's policy.

In your pre-purchase analysis, also take into account:

• Design and aesthetics: particularly important for furnishing homes or public spaces.
• Space requirements: consider the floor space needed for the purifier.
• Ease of installation and mobility: look for ease of installation, moving, and fixing.
• User autonomy and automatic functionality: the ability to adjust the device easily and the presence of automatic functions for convenience.
• Connectivity to sensors: option to connect the device to a sensor for fine-tuning settings based on regular measurements.
• Manufacturer support: availability of customer support and a hotline.
• Warranty and return policy: consider the terms of warranty and return policies.
• Preference for locally made products: products made in France and those without planned obsolescence.
• Labels and Certifications: look for guarantees of equipment quality.
• Corporate Social Responsibility and eco-friendliness: consider the company's commitment to CSR and eco-responsibility policies.

Sources and references

1. For more details on the different types of pollutant, see our article Air pollution: are we too careful? https://www.teqoya.com/air-pollution-are-we-too-careful/
2. See, for example, our article on wood dust, the first in a forthcoming series on occupational illnesses linked to poor air quality https://www.teqoya.com/dust-wood-pollution/
3. In the working environment in particular, better IAQ reduces absenteeism and sick leave and improves performance. See our article Air quality in offices and other workplaces: does it impact business performance? https://www.teqoya.com/en/quality-of-life-at-work-productivity-quality-air/
4. Effectiveness Of Home Air Cleaners In Reducing Indoor Levels Of Particles: https://www.researchgate.net/publication/236004768_Effectiveness_of_Home_Air_Cleaners_in_Reducing_Indoor_Levels_of_Particles