Do air purifiers work? what can we expect from them?

ByFields Corrielus 2019-06-20 317

We are widely aware of the issue of outdoor air pollution. Many people think that they no longer breathe anything harmful once they get home. However, our indoor air is often much more polluted than the outdoor air! Hence the legitimate questions: To whom is it addressed? How does it work? Is it effective? Our first tests allow us to see more clearly...

Fine particles are a hot topic, but once we get home, we continue to breathe polluted air; it is even much more so than the outside air - and of a different nature. According to the Ministry of Environment, some pollutants are present only indoors while others "are present both indoors and outdoors but in different concentrations. For some pollutants, we can observe a concentration up to 15 times higher inside than outside". The WHO's findings are clear: "Air pollution, both indoor and outdoor, is a major environmental health problem affecting both developed and developing countries". And this pollution causes discomfort or respiratory diseases; it is also at the origin of various diseases, strokes or heart disease. However, becoming aware of this is not easy because "the air and indoor air pollution are not visible", explains Christophe Dolain, product manager at Aldes.

If people with allergies or asthma suffer from visible symptoms, for everyone else, this pollution is imperceptible. Some people choose to equip themselves with an air purifier; moreover, more and more manufacturers are marketing them. But are these devices necessary? And above all, what results can we expect from it?

air purifiers

Actions to limit indoor pollution

To fight polluted air, the first advice is to aerate twice a day for a few minutes; this is valid even in the event of a pollution peak, but the outside air remains less polluted. In this case, it is advisable to do it early in the morning or late in the evening.

"Human activity" also causes pollution and although it is difficult to avoid certain "polluting" actions (such as cooking), others can be limited: burning incense or candles, spreading perfume, smoking indoors or using cleaning products (some are not essential).

Since 2001, there has been an Indoor Air Quality Observatory in France, whose mission is to apprehend indoor pollution and provide advice. The dedicated sheet "The right actions for good air" is full of advice.

What is it necessary to filter in our indoor air?

In addition to its invisibility, the complexity of this pollution lies in the large number of pollutants of various kinds, as explained by the Ministry of the Environment on its site: "the sources of indoor air pollution are multiple: outdoor air, certain construction materials, combustion appliances, equipment, furniture, maintenance and DIY products, human activity (cooking, etc.), etc.), the lifestyle of the occupants (smoking, insufficient ventilation, etc.), biocontaminants (house dust, dust mite and cat allergens), etc."

There are three main categories of pollutants:

- of a chemical nature: building materials, furniture, decorative items, maintenance and DIY products. They release polluting particles from adhesives and various materials (including volatile organic compounds (VOCs), including the famous formaldehyde) without anyone being aware of it....

- Physical in nature: asbestos, suspended particles (by transfer from the outside, for example related to road traffic; emitted by combustion such as tobacco, candles or incense; by cooking food or household activities), radon...

- Biological in nature: moulds, bacteria, viruses, pollen (heat, humidity, poor maintenance of premises and installations dedicated to hot water and air conditioning promote the proliferation of biological agents, which increase the risks of diffusion in water or air)...

Biological in nature: moulds

Dangerous particles

Some particles are more dangerous than others: they are the smallest particles that enter the body, lodge in the lungs and in the blood. According to the WHO, all those smaller than 10 microns should be considered dangerous. They are commonly referred to as PM10 (PM for Particulate Matters). To get an idea of their dimensions, it is necessary to know that a hair measures 60 microns, pollen up to 40 microns...

Dangerous particles

Among these dangerous particles are also the famous fine particles, known as PM2.5 (2.5 microns and less): they are produced by industrial emissions and road traffic. Indoors, they come from cigarette smoke, cooking fumes, burning incense, candles, chimney fires, sprays, cleaning products and human activity...

VOCs from glues and chemicals in furniture, building and decorative materials (such as paint solvents), certain cleaning products, etc. are also found. According to WHO, formaldehyde (the most well known) is present in all interiors of the world "at concentrations that are harmful to health" (WHO indicates: benzene, carbon monoxide, formaldehyde, naphthalene, nitrogen dioxide, polycyclic aromatic hydrocarbons, radon, trichloroethylene, tetrachloroethylene). There are more than a hundred VOCs that pollute our interiors.

Other particles (such as pollens and allergens) are not considered "dangerous" but still deserve to be filtered.

Other particles (such as pollens and allergens)

The operation of the air purifier

Purifiers promise to filter most of these indoor pollutants. They all work almost in the same way, by recirculating the air. They suck it in, filter it and then propel it "purified" into the house. Generally, there are several filters one after the other, or even a single filter grouping these different layers (this is the case at Dyson or Philips).

A pre-filter generally collects the thickest particles (animal hair, hair...). The air then passes through an activated carbon filter, which has absorbent power and therefore retains odours, fumes, certain organic compounds and gases (it is the same type of filter as in kitchen extractors). Finally, the HEPA (High Efficiency Particulate Air) filter, as in vacuum cleaners, retains fine particles, with a purification efficiency level that would go up to more than 99.9% (according to the standard, because this measurement is performed under very specific conditions).

It should be noted that some devices also integrate other processes, such as photocatalysis, ionization, UV or ozone (see box).

What do purifiers filter?

The ability of purifiers to retain pollutants depends on several things, including particle size. Most manufacturers report being able to filter particles up to 0.3 micron and over 99% (HEPA filter). Mélanie Bouquerel, product manager at Rowenta, explains that anything considered to be pollution of physical origin (particles large enough to be visible) or biological (moulds, dust mites, pollens...) can a priori be eliminated by doing a lot of cleaning but returns very quickly. If an air purifier is used, these particles are normally treated by the HEPA filter with a very promising retention level.

According to the tests we carried out in the Digital Laboratory, the promise is being kept. As our particle counter is able to take into account particles up to 0.3 micron, all the purifiers tested have decreased (more or less quickly) the number of particles significantly: installed in a room where our counter identifies more than 100,000 of these fine particles, they bring the level below 5,000 particles, or even 3,000.

Substances that can resist them

For some substances, it is more delicate. This is the case for VOCs because, as their name suggests, they are particularly volatile and difficult to trap. The activated carbon filter should be able to capture these substances, but there is still a risk of release, as most manufacturers tell us, sometimes about the "quality" of the filter, sometimes about the quantity of carbon contained or even about the limited life of the activated carbon (which would be much shorter than that of the filters, at most 1 month). Rowenta admits that activated carbon filters are able to absorb some of these substances, but not the most volatile (such as formaldehyde) in a satisfactory way, hence the choice to trap them in a specific filter (NanoCaptur) that modifies the molecules to prevent them from escaping.

Christophe Dolain, product manager at Aldes, who offers a centralised purification solution, explains that the best solution to eliminate indoor pollution is not to recycle the air but to renew it. Indeed, with its centralized solution (connected in addition) InspirAIR Home, Aldes proposes to expel the polluted air outside and filter air that is brought in from outside. VOCs would thus be expelled... out.

This solution would also eliminate CO2, a substance that "cannot be trapped". If the solution is attractive, its cost is much higher than that of a conventional purifier and requires work to pass ducts through the false ceilings or attics of the house to be treated.

We have made some measurements of the formaldehyde level, taking as a benchmark the WHO recommendations: "a guide value of 0.1 mg/m³ over a period of 30 minutes is recommended to prevent sensory irritation in the general population. This guide value (...) also prevents the effects of long-term exposure on lung function or cancer risk.

First of all, in a perfectly sealed room, the formaldehyde level is 0.08 mg/m³ at its maximum level. And surprisingly, in a less waterproof room (despite our large furnished premises which have undergone a number of works), the average is extremely low and our measuring tool detects almost no formaldehyde. However, a spray of deodorant is sufficient to explode these values: 0.3 mg/m³, three times the "permissible" concentration. After an hour (it's a long time), a model like the Rowenta Intense Pure Air managed to get the rate back to its initial level (almost zero). In the same room, 5 minutes of window opening offer the same result. The combination of the two seems to us to be the ideal solution when using cleaning products.

On the other hand, we did not carry out any tests on the duration (in relation to the lifetime of the activated carbon).

An efficiency that depends on certain criteria

Obviously, the efficiency level of the purifier and its speed of treatment depend on the state of pollution of the room and its dimensions; it is of course necessary that the device is adapted. The effectiveness of air purification will also depend on a few points.

The air flow rate and especially the CADR (Clean Air Delivery Rate, i. e. the volume of purified air it is capable of delivering) must be adapted to the size of the room to be treated and even ideally to the entire fireplace. Indeed, we have noted that the number of particles in a "purified" part tends to rise sharply when the door is opened (by about 20%). This must be taken into account when choosing the device and using it.

The quality and condition of the filters. It is important to ensure that they are changed regularly. Because if they are dirty, the device in automatic mode increases its operating speed, which can lead to overconsumption and an increase in noise level. And if it is an activated carbon filter, its efficiency in "capturing" certain substances may be reduced. Some purifiers on the market notify the user when the filter needs to be changed, even blocking the use of the device.

The auto mode is particularly practical: the purifier detects the level of pollution and adapts its operating speed. However, for it to be effective, its sensors must be accurate and have a sufficient range of action (our tests were performed with the particle counter on the opposite side of the room from the purifier).

Can we trust them?

It is impossible to say that purifiers transform our interiors into healthy "bubbles", without any pollutants (no manufacturer is committed to this anymore: all evoke an efficiency of more than 99% on pollens and allergens) or to conclude that we feel a perceptible well-being when we are neither allergic nor asthmatic. But is that the goal? As Angélique Delpech, head of the air treatment category at Philips, states, "The purifier is not to be considered a medicine, but it helps to combat the effects of various sources of indoor pollution (...). (Philips) believes that its mission is to support and relieve, because air pollution affects everyone.

If there is any doubt about the effectiveness of purifiers on VOCs and in particular in the long term, our measurements confirm a significant efficiency on the rate of suspended particles, even fine particles (provided that the filters are kept clean).

The choice to equip yourself with a purifier is very subjective because the idea of living in polluted air is anxious for some people; on the contrary, others find the idea of having to purify everything everywhere scary. As for allergic or asthmatic people, by choosing a suitable model, they will undoubtedly perceive a difference and can avoid unpleasant symptoms.

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