How Do Air Purifiers Work

While some air purifier shoppers shop this way, we think it is very important to be well-informed on filtration systems used in a home air purifier.

The main reason is because each air cleaner has different filtration technologies which are pertinent to what it is supposed to do. Thus, an air purifier marketed for removing volatile organic compounds has different air purification system from the ones marketed to remove bigger air particles only. Therefore, to make sure you get the right product, you must know exactly what purification technologies are employed by a particular air purifier and what contaminants it is capable of removing.

How Air Purifier Works

HEPA Air Purifiers

Carbon Air Filter – How Does It Work ?

So how does a carbon air filter work ?

Carbon air purifier works by trapping or absorbing gas molecules down to 0.001 micron or smaller, into its tiny pores. So you see, in order for a carbon air filter to do its job, it needs to have tiny pores to trap gases.

But how come a carbon has tiny pores ? Carbon can be made to have tiny pores by heating and steaming it. Carbon with tiny pores is said to be activated.

Once these tiny pores are saturated with gas, the carbon filter won’t be able to absorb anymore contaminant. At that point, you would need to replace it.

To prolong the life of a carbon air filter, it is important to have a good pre-filter so that the pre-filter can filter out the higher molecular-weight particles, leaving only gases for the carbon to absorb. That’s why you never find a gas air purifier with only a carbon air filter in it. A carbon air filter is always be an add on to either a HEPA air purifier or an electrostatic air purifier. Therefore, if you want to buy a carbon air purifier to control gases, then you would have to buy a HEPA air purifier which has either chemical or carbon air filter added to it.

What Does a Carbon Air Purifier Remove ?

Carbon air filter removes any gases which are in the range of 0.001 microns or smaller. These gases are usually volatile or semi-volatile organic compounds. Smoke and pet odor are included here.

However, carbon air purifier is not effective in removing gases if installed in humid conditions where the air has  lots of water molecules in it. If you live in such condition, you would need a chemical air purifier to address the gas problem just because carbon would not be effective here.

Equally, carbon air purifier also does not filter the smaller molecular weight gases including all inorganic gases like ammonia and a minority of organic gases such as formaldehyde. If you need a gas air filter for filtering the gases I mention above, then you need to buy an air purifier designed specially to get rid of gasses which also has chemical absorbent.

So how does a chemical air purifier work ?

Chemical air purifier works by removing gases through chemical reactions. Basically, the chemicals – also known as Chemisorbers – reacts with the water molecules in the air and also with gas molecules to break them chemically into harmless forms such as carbon-dioxide. This way, unwanted gases are removed. A chemical air purifier usually uses chemisorbers which may include alumina oxide, alumina silicate, and potassium permanganate.

Gas Air Purifier Buying Guide

There are several things you should know prior to buying a gas air purifier

First, you need to know what kind of gas you want to remove. If you want to get rid of volatile or semi-volatile organic compounds such as smoke and pet odor, then you can buy an air purifier containing a carbon air filter. However, if you want to remove small molecular weight gases such as inorganic gases and formaldehyde, you should buy an air purifier with chemical absorbent in it

Second, look out where you live or where you would like to use the gas air purifier. A carbon air purifier would not work well in a humid place. So, if you want to get rid of gases in this place, then you should get a chemical air purifier instead.

Third, when shopping for a gas air purifier, look for the one with decent pre-filtering capability. You want all the big particulates to fall into pre-filters first, leaving only the carbon or chemical absorbent to deal with gas. If the pre-filtering stage does not work well, then the carbon or chemical air filter will have to deal with the big particulates as well, hence saturating it prematurely. Therefore, ideally, a gas purifier should have a pre-filter which can trap big particulates and a HEPA filter which filters particulates up to 0.3 micron. This way, the carbon or chemical air filter only deal with gases.

Fourth, look into the design and amount of carbon or chemical absorbent contained inside a gas air purifier. In order for a carbon or chemical air purifier to work effectively, it needs to have at least 15 pounds of absorbent. Most discount gas air purifiers do not have such amount of absorbent. Instead, they only have ounces of it, which is not enough to make a difference. In addition, the design of the absorbent can play a role in determining the effectiveness of a gas air filter. You would want to have a carbon air purifier which has carbon air filter in pleated design. This design enables the filter to have larger surface area. This makes the filter capable of passing and filtering large amounts of air.

What are Electrostatic Air Purifiers (How do They work)

Electrostatic air purifier as such is a kind of ionic air purifier. Like other ionic air purifiers, it charges or ionizes air particles. The machine then draw those charged particles into the collection plates which are charged with different polarity from the particles. So, if for instance, the machine charges particles with negative ions, then the collection plates should be charged positively. Because of the opposite polarity, the ionized particles can stick easily to the collection plates of an electrostatic air cleaner. This kind of machine, when used in industry, is also called an electrostatic precipitator because it collects charged particles inside the machine.

The electrostatic air filtration system is pretty efficient in absorbing particles as long as the machine is good enough in charging the particles, can produce a strong charge on the collection plates and has a large total area of the collection plates. This will ensure that most of the incoming particles are charged and there is enough space for all those charged particles to stick to the collection plates. If either one of that three factors are not good enough, the efficiency of the machine will plummet. Also, entering the equation is the optimal use of fan to ensure that air flows fast enough into and out of the air purifiers.

Since an electrostatic air cleaner theoretically can charge a wide range of particles size-wise, then in a good machine, an electrostatic air purifier can curb particles up to 0.1 micron in size. So in a sense, it can be comparable to a HEPA air purifier because a True HEPA filter can trap particles optimally up to 0.3 microns and at a reduced efficiency – up to around 0.1 micron.

Types of Electrostatic Air Cleaner

By Stages

There are several different types of electrostatic air purifiers based on the number of stages it has for cleaning up air:

• One stage.
  Some electrostatic precipitators use a one-stage system to clean the air. In this kind of machine basically, the air purifier charges the outside particles, draws the charged particles in and stick the particles to the plate. Therefore in this method, the particles only undergo one step once inside the air purifier, which is sticking to the collection plate.

• Two stage
  This type of electrostatic air cleaners first draw the dirty air in, and once the air is inside, the air purifier does two things to them:
  • Charge them using high-voltage wires.
  • Pull the charged particles to the collection plates.

• Many stage
  Some electrostatic precipitators combine the electrostatic air filtration method with mechanical filtration to increase the efficiency, through the use of a prefilter.

By The Types of Collection Plates

Different electrostatic precipitators use different types of collection plates. They can be divided into three groups:

• Electrostatic air cleaners with an original collection plate.
• Ionic air cleaners with electrostatic air filter. In essence, this is a charged filter which acts as a collection plate. It’s much more efficient to have an electrostatic air filter than just metal collection plates because a charged filter trap particles in two ways:
  • Through the use of charge.
  • Through its property as a filter.

  This way, some particles which manage to get into the air purifier and not charged or weakly charged (usually the small ones) can still be arrested, whereas plate collector will only trap charged particles. One of the premium air purifier manufacturer, BlueAir, uses this kind of filter, and therefore their air purifiers manage to achieve high efficiency, have above average air flow and are silent.

• Electrostatic air purifiers with modified collection plates.
  Honeywell electrostatic air purifier uses IFD (intense field dielectric) plates instead of the oldie goldie metal collection plates since IFD plates have been proven to deliver stronger charge and can afford being dirty without resulting in crackling noise or electrical break. With the ordinary electrostatic precipitator plate, when the plates get dirty, they decrease dramatically in efficiency and produce crackling noise. This is not the case with the IFD plates. Therefore, if you own an electrostatic air purifier with IFD plate, you don’t have to wash the plate that often.

The Positive Aspects of Electrostatic Air Purifiers

• Silent or not noisy.
  An electrostatic air purifier is definitely more silent than a HEPA air purifier because its fan does not have to work that hard to push the air through a filter. In a HEPA air purifier, the fan has to work at high speed so that the air can flow fast enough through the filter. It is even more pronounced in a HEPA air purifier with a tight housing because the pressure is greater. In contrast, electrostatic air cleaner ‘breathe’ more easily because there is no filter which acts as a barrier for the air to go through. It allows the fans to work less harder, and therefore produce much less noise.
• No filter replacement.
  If you own an electrostatic air cleaner which does not have any media filter to change, then you don’t need to change anything. This is one factor where owning an electrostatic air purifier instead of a HEPA air purifier can save you money. Just be prepared, though, that in order to keep your machine in a tip top condition you should provide a sweat equity instead (see below).

Potential Drawbacks of Electrostatic Air Purifiers

• A lot of plate washing or wiping.
  Yup, as much as you love the saving money aspect as a result owning an electrostatic air cleaner which does not need any filter replacement, you should know that in order to keep your unit works with high efficiency, you need to wash the collection plate regularly. As the collection plate collects dust and its surface covered with particulates, their ability to attract the particles decreases until the plates are taken out and cleaned. The efficiency can start out high around 80-s and can degrade to as little as 20% if the plates become dirty. Besides, the machine will give out pop and crackling sound when the plates get dirty. Hard scrubbing may even be needed if your collection plate becomes so dirty. If you hate this kind of maintenance, get either a HEPA air purifier or an ionic air purifier which utilizes electrostatic air filter or IFD plates (see above) instead.
• Ozone emission
  Due to the high voltage required to produce an electric field in electrostatic air cleaners, this type of air cleaner produces some amount of ozone. EPA gives a limit of 50 ppb (parts per billion) ozone to any electronic device to ensure safety. However, a small number of air purifiers which do not follow these guidelines still manage to find their way to the residential air purifier market. So you need to be careful of those. Fortunately, there are a small number of electrostatic air purifiers which do not emit ozone or emit a background/negligible amount of ozone. Since ozone is a lung and soft tissue irritant, those who suffer from asthma or other lung diseases are better not to touch these machines with a 10-foot pole unless you know for sure that they are ozone-free. Online vendors or the manual can give you information whether a particular product is ozone-free.

Types of Ionic Air Purifiers and How They Work

Some ionic air purifiers send charged ions out of the machine, so they can attach themselves to air particles while others draw the air particles in and subsequently charge them. Either way, the results are the same. Air particles are charged or ionized.

Hence, we actually have two types of ionic air purifiers: a simple ionizer air purifier, and electrostatic precipitator air purifier.

A simple ionizer air purifier sends charged ions out of the machine and then lets the charged particles to settle to a surface, ready to be wiped out by the home owner.

In contrast, an electrostatic precipitator air purifier collects the charged particles in a series of metal plate collectors inside the machine. Hence, while a simple ionizer simply makes the airborne particles to settle because of the charges and does not do anything to actually remove the particles, an electrostatic precipitator draws the charged particles into the machine.

Since a simple ionizer air purifier just moves the airborne air particulates to various surfaces, it is not effective enough to clean up air when used on its own. Therefore, most air purifiers have ionizers only as an add-on or optional filtration technology to a HEPA air purifier.

if you are looking for an ionic air purifier with no HEPA filter, a more appropriate approach is by purchasing the ones which draw the charged particles in and collect them in a series of plate collectors, which are also known as electrostatic air purifiers. That way, those dust are removed from the room.

NOTE: Follow the link for more discussion on whether ionic air purifiers work and which ones work.

Yet, another way to do it, is by using another kind of ionization which indirectly produce hydroxyl radicals, known as plasma technology.

In this scenario, the ionizer releases partially charged particles which, in the presence of water vapor from the air, can turn into hydroxyl radicals. Hydroxyl radicals, like ozone, are unstable and highly reactive. They readily attack volatile organic gases, viruses, bacteria and other gases; either killing them or changing the chemicals into harmless air molecules. After the reaction takes place, the hydroxyl itself changes into water molecules. Therefore, unlike conventional ionizer air purifier which merely turn the suspended air particles into settled air particles, plasma technology really removes the air pollutant from the room by converting them into harmless chemicals.

The hydroxyl radical production technology or plasma technology is wonderful when used concomitantly with other filtration technologies, such as HEPA filtration since they complement each other well; HEPA being a superb filter for particles bigger than 0.3 micron, and plasma technology being an excellent fine-particle remover. In addition, as an oxidizer, they are very short-lived and unlike ozone, they won’t hang out in your house for days. Therefore they are safe to use. By the way, this technology has been used in conjuction with other air filtration technology with good results by Plasmacluster air purifier by Sharp and Winix Plasmawave Air Cleaner.

Ionic Air Purifier – Is It Safe ?

Due to the high voltage required to produce electric field in electrostatic air cleaners, ionizing air purifiers produce some amount of ozone. EPA gives a limit of 50 ppb ozone to any electronic device to ensure safety, but it is important to understand that 50 ppb of ozone is not background ozone and is not negligible. This means, that you will be able to smell the ozone and sensitive people may not be able to stand it. Ozone is a powerful oxidant and can irritate soft tissues such as our eyes as well as respiratory pathways. Lung sufferers, in particular, are better off not to go near to any of ozone-producing ionic air purifiers because of high possibility of respiratory pathway irritation.

Potential buyers need also to know that although EPA has set up a limit of ozone production, a small number of air purifiers do not follow this guidelines and yet, they still manage to find their ways to the residential air purifier market.

With all this information, does it mean you have to avoid ionic air purifiers altogether ?

We think that you should avoid ozone-producing ionizing air purifiers. Fortunately, there are a small number of ionizer which do not emit ozone or only emit a background/negligible amount of ozone. Online vendors or the manual can give you information whether a particular product is ozone-free.

Positive Aspect of Ionizer Air Purifiers

• No filter replacement required.
• Quieter than HEPA air purifier. This is because the unit breathes better, as opposed to a HEPA air purifier unit which has a filter barrier. Therefore, the fans of an ionizing air purifier does not have to work hard to push the air through the air purifier.

Negative Aspects of Ionic Air Purifiers

• Many ionizers are ozone producing and therefore are not safe.
• Owners of electrostatic precipitator has to wash the metal collection plate often to ensure the continued effectiveness of the unit.
• Owners of simple ionizers which does not collect air particles, may not find the unit to be effective at all since ionizers just move the dust from the air to a surface and do not actually remove the dust from the room.
• In general, ionic air purifiers are less effective than HEPA air purifiers, unless the ionic air filtration technology is combined with the HEPA air filtration system. Otherwise, a pure ionic air purifier can only, at maximum, provide all around cleaning and is very unsuitable to address people with problem, such as allergy, asthma, smoke, and so forth.

What is an ozone air cleaner ?

Ozone air purifier is a type of electronic air purifier which is frequently used to remove odors and sanitize (kill mold or mildew), and works by emitting ozone. Ozone is a powerful oxidant and is very reactive. Upon ozone emission from an ozone air purifier, the reaction between the ozone and gas particles takes place. As a result, new chemicals are formed, hence odors are removed. Since an ozone air cleaner works by emitting huge quantities of ozone, this type of air purifier is sometimes also called ozone generator.

Ozone Air Purifiers in-review – Is it safe and effective ?

Ozone generator is probably the cheapest kind of air purifiers to buy and maintain, hence it is quite popular. However, before you rush out to buy one, it is important to know that Environmental Protection Agency (EPA) has issued a warning regarding this electronic air cleaner.

In their reviews, this agency expresses concern on the safety of the use of an ozone generator at home. Now, you may think that ozone is good. While ozone is good when it’s in the stratosphere, it is not something you would like to have in our atmosphere.

It is because ozone is known as a respiratory irritant. So even at low concentration, as determined by EPA (50 ppb or part per billion), it is still something to be avoided, especially for people with respiratory diseases including asthma.

Many ozone air cleaner’s manufacturers claim that their air purifiers are safe and are well within the limit of EPA (50 ppb) if used in a room no smaller than the manufacturer’s recommendation. However, according to EPA there are still several problems with that:

• First, there are many customers who are not fully aware with ozone’s danger and put an ozone air cleaner in a much smaller room, hence increasing the ozone concentration to an unacceptable level.
• Second, the ozone level selectors in the ozone purifiers are not precise. For instance, although it says that such and such level should produce this much of ozone, in reality, the quantities of ozone emitted from the purifier are generally more than the intended levels.
• Third, EPA found that at the concentration acceptable to EPA, it actually does not work effectively.
• Fourth, the ozone is supposed to react with the chemicals in the room and in the process converts the existing chemicals into the new ones. EPA is concerned about this new form of chemicals because no one can even be sure that the new form of pollutant is not more dangerous than the previous one.

Based on those arguments, EPA suggested in their reviews NOT to purchase any ozone generator to clean air since there’s too much risk associated with it, and EPA does not see much effectiveness in removing gas particulates.

Indeed, initially, ozone generators were only used in the hospitality and/or restoration industry because it was cheap to buy and maintain. Its usage was only limited on rooms or houses where nobody was present. Remember, to be effective, the ozone quantities should be high and ozone is not safe in that quantities for both human being and animals. Hence, ozone air purifiers are only used, for instance, to clean up the smoke and odors of empty hotel rooms. It is also often used in restoration industries to remove musty smell from a flooded house, the smoke odors from a house that had been on fire, and so forth. In all application, after the cleaning finishes, the windows and doors are opened and rooms are left empty until all ozone has gone out of the rooms.

So you see, ozone air purifier is mainly used to get rid of smoke and odors in places not normally occupied for a while. It is important also to note that even at high concentration, it can only remove some gases/odors. It does not trap bigger particulates such as dust, pollen and many air-borne particles.

To address this problem, some home ozone air cleaner’s manufacturers add air ionizer into the machine. Hence you will have an ozone ionizer air purifier combo. Basically, what an air ionizer does is to ionize big particulates in the air. Once ionized, the particulates will literally fall down to the floor, and can be vacuumed. However, air ionization is not an effective way to remove particulates since the ionized particulates can also stick to the walls. In addition, even if the particulates fall down to the floor, they often lose the ionization, so they come back into the air again. Hence, the effectiveness of a combo ozone ionizer air purifier is questionable.

Suffice to say that the use an this electronic air purifier in a home setting where living beings are continuously present is controversial. Aside from the fact that it emits dangerous gas (ozone), its effectiveness in cleaning up the air is also questionable, especially if used at a concentration deemed to be “safe” by EPA.

So, if you ask us what the best ozone purifier is, we don’t have the answer because we can’t even recommend any ozone generator for home use.

So How To Remove Odors and Smoke Then ?

There are other methods by which an air purifier can remove odor and smoke without the danger of ozone emission. Since odor and smoke are basically gases, an air purifier with enough carbon or chemical absorbant will do the job. For a more thorough discussion on chemical and carbon air purifier,click here.

Otherwise, click here for more specific discussions on air purifier for smoke removal.