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Air purifiers, on the surface, may seem deceptively simple — dirty air is drawn in through a vent and clean air is blown out. But the quality and technology of the mechanisms and filters inside these machines can make all the difference in determining just how effective they are at cleaning indoor air.

In this post, we break down exactly what an air purifier is, why you may want one in your home, and what you should know about the different types of air filters.

What is an air purifier, and how does it work?

Air purifiers are designed to get rid of odors, allergens, dust and other unwanted airborne substances. Most have two main parts: a fan and a filter. The fan’s job is to circulate the air in a room by sucking in air and forcing it back out through the filter. As the air passes through the filter (or, in the case of some models, multiple filters), pollutants become trapped in it. If an air purifier is working well, the air that has passed through it will contain fewer pollutants than the air that has not passed through it.

There is a wide variety of air purifiers on the market today. These units not only vary in size and price, but also in quality and technology. Whether you are looking to purchase an air purifier for home or business use, consider the following:

  • The room size it is approved for;
  • The type of filter it uses (which will affect the type of pollutants it removes from the air);
  • How often you will need to clean or replace the filter;
  • The cost of replacement filters;
  • The design of the purifier (how bulky it is);
  • How loud the purifier is at different speeds.

Much of this information can be found on a product’s box or manufacturer website. Online reviews and videos are also helpful sources of information on how an air purifier performs in real-world situations.

Why you may want an air purifier: Types of indoor air pollution

Not all air purifiers are created equal, and the same can be said of airborne pollutants. There are a wide variety of contaminants that can impact the quality of indoor air. For example, sources of air pollution include particulate matter, volatile organic compounds and bioaerosols. Exposure to each of the different types of airborne pollutants may lead to various adverse health effects.

Particulate matter (PM)

Particulate matter pollution is one of the most commonly discussed sources of bad air quality. It is a mix of solid particles and liquid droplets suspended in the air. PM can range in size, from dust (and dirt particles that you can see with your eyes) to tiny particles that can only be seen with a microscope. Because these particles are so small, they are very easy to breathe in. Often, you may not even realize you are being exposed to PM.

The smallest particles — those less than 10 micrometers in diameter — are the ones that can have the most severe health effects because of the ease with which they can enter the lungs. Particles that are less than 2.5 micrometers in diameter can go a step further, in some cases leaving the lungs and entering the bloodstream and internal organs to cause even more damage. PM exposure can contribute to health problems, such as:

  • Nonfatal heart attacks;
  • Irregular heartbeat;
  • Aggravated asthma symptoms;
  • Decreased lung function;
  • Increased respiratory symptoms.

Volatile organic compounds (VOCs)

Volatile organic compounds are a group of gaseous pollutants that affect indoor air quality. These compounds are often byproducts of industrial manufacturing. They can also be found in common household products, including cleaning products and disinfectants, paints and solvents, aerosol sprays and pesticides. Many hobby supplies, such as craft glue, also contain VOCs.

The term VOC covers a wide range of substances, not all of which are harmful to human health. However, many can cause allergic reactions in sensitive individuals. Symptoms of VOC exposure may include skin reactions, nose and throat irritation, headaches, nausea, dizziness and fatigue.

The Environmental Protection Agency (EPA) specifically recommends reducing exposure to these VOCs:

  • Benzene: Benzene can be found in cigarette smoke, vehicle exhaust and paint supplies. According to the Department of Health and Human Services, long-term exposure to high levels of benzene can cause cancer in humans.
  • Methylene chloride: A suspected carcinogen, methylene chloride can be found in paint strippers, adhesive removers and aerosol spray paints.
  • Perchloroethylene: This is the most common chemical used in dry cleaning, and it is also a suspected carcinogen.


Though some (but not all) bioaerosols may technically be PM, they deserve a special category because of their unique characteristics. Bioaerosols are particles that are emitted or released from living beings, though they are not always alive themselves. These can include:

  • Mold: A type of fungus, mold spreads by releasing airborne spores. Mold spores can be found virtually everywhere, though they are too small to be seen with the naked eye. Some people, including those with allergies or asthma, may be more sensitive to mold exposure and experience health effects from exposure, such as coughing, wheezing, stuffy nose, sore throat, skin rashes and eye irritation.
  • Bacteria: Like mold spores, bacteria are abundant in both indoor and outdoor air. Bacteria are a mostly harmless, natural part of life. In fact, some types of bacteria are necessary for our survival. However, certain strains, such as strep and staph, may cause serious illness.
  • Viruses: Another common airborne pollutant, viruses are often found in the air in quantities too small to affect humans. Many viruses, like the flu, spread through liquid respiratory droplets that do not stay in the air for long. However, airborne transmission is possible for some viruses.
  • Allergens: An allergen is a substance that triggers an immune system reaction. Though these substances are not dangerous, the immune system attacks them as if they were a serious threat to your health. Common household allergens include pollen, pet dander and dust mites.

What are the different kinds of air purifiers?

The two main types of air pollution — gaseous pollution and particulate matter — can be removed from the air using specific types of filters. Not all air purifiers are equipped to handle the same kinds of airborne pollutants. If you are shopping for an air purifier, you can tell which pollutants it deals with by the type of filter it contains. The main types of air purifiers you will come across are:

HEPA filters

A HEPA filter is a type of mechanical filter that meets a standard of removing at least 99.97% of airborne particulate matter with a diameter of 0.3 micrometers (Note: Only true HEPA filters meet this standard. Other mechanical filters, sometimes marketed as HEPA-type filters, may trap PM at lower percentages). These filters are made up of a dense fiber mesh that traps particles as air flows through them.

Unfortunately, while HEPA filters can remove a large percentage of particles from the air, they have no effect on gaseous pollutants, such as VOCs. If you are looking at an air purifier with a HEPA filter, check to see if it contains a second filter (most often a carbon filter) that can filter gaseous pollutants from the air.

Carbon filters

Unlike HEPA filters, carbon filters can remove gaseous pollutants, including VOCs, from the air. These filters are made with activated charcoal or another form of carbon. A process called adsorption causes chemical gases to stick to the outside of the carbon when air passes through the filter. Typically, these filters have a lattice structure to increase the surface area available to adsorb gaseous pollutants.

Carbon filters can effectively remove VOCs and other toxic gases from the air, but they are ineffective against particulate matter. Because of their lattice structure, particles can simply pass through the holes in the filter.


Instead of using physical filters, ionizing air purifiers use an electric current to charge particles in the air. These charged particles are called ions, and they are attracted to particles and surfaces with an opposite charge. When ions adhere to other particles in the air, it creates a heavier, larger particle that will eventually settle on the ground or another surface instead of remaining in the air. Charged particles may also attach themselves to surface areas, such as walls, furniture and flooring.

There are two main drawbacks to ionizers. First, they do not trap pollutants (unless they have a charged plate that attracts ions). Particles that have settled on the surfaces in your home can easily be kicked up by air flow or human activity. Second, many ionizers produce ozone as a byproduct, which is a pollutant in itself and can cause adverse health effects.

Ozone generators

Ozone generators may be marketed as air purifiers, but they offer no real air purification benefit. The idea is that the ozone generated by the machine should react with pollution in the air to turn it into harmless carbon dioxide, oxygen, and water. However, ozone generators are not effective at removing any type of pollution from the air. Not only that, but they actually create ozone pollution. The EPA warns against using ozone generators in the home, as they can produce ozone at levels that are considered harmful to human health.

PECO technology

Photoelectrochemical oxidation (PECO) technology — the technology found in Molekule air purifiers — removes pollutants from the air through a light-activated chemical reaction. This process traps larger particles and destroys organic pollutants at the molecular level, including VOCs and bioaerosols such as mold spores, viruses and bacteria.

However, inorganic pollutants cannot be destroyed by this oxidation process. To address this, Molekule air purifiers use an additional Pre-Filter that traps many of the airborne particles that may not be affected by the PECO filter.

PECO technology neutralizes airborne organic pollutants without creating harmful byproducts, such as ozone. In fact, ozone is one of the many forms of pollution that Molekule air purifiers can remove from the air.

As you become more aware of the many types of pollution found in indoor air, it is a good idea to learn more about how to protect yourself and your loved ones. Now that you know more about air purifiers and how they work, you will be better equipped to choose the right one for your home or office.

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