How Do Air Purifiers Work?

Many allergy suffers, as well as anyone else interested in the air quality in their homes and offices should consider an air purification system to control the levels of indoor pollution. Exposure to this pollution can result in respiratory issues, lung infections, and other illnesses. Removing pathogens from the environment can ease these symptoms and make for a cleaner, healthier home or workplace.

The ultimate guide to air purifiersAir purifiers are used in a variety of residential and commercial applications to rid the air of contaminants and make breathing easier. There are a variety of purifiers, utilizing differing technologies for different situations.

Some are intended to adhere to very strict air purity standards and are used in settings such as manufacturing, hospitals or other areas where very pure are is required. Others are used in less sensitive settings, such as the home, to make the air cleaner and more enjoyable to breathe.

Development History

The first air purifier would have been simply an open door or window. This would have allowed dust and other particles to be blown out of the house or building, and clean air to flow in. But this primitive technique would have been impractical in cold climates and where the outside air was contaminated.

In the early 1800s, as the industrial revolution took hold, scientists started looking for ways to purify the air. The first recognized air purifier was developed by scientist John Charles Dean as a mask that allowed firefighters to enter building buildings without having to breathe smoke and other pollutants.1

In 1854, John Stenhouse developed a mask based on a charcoal filtering design that was intended for use by divers and coal miners. The mask filtered impurities from the air, including both particles and noxious gasses from the air. Stenhouse’s mask represented the first significant advance in air filter technology since the simple filter mechanism.2

Charcoal treated with oxygen became porous, allowing for gasses to pass through, while contaminants were chemically bound to the carbon in the charcoal. This way, dust, poisonous gasses and other contaminants were trapped, while lighter gasses in the air were allowed to pass through the filter.3

An improvement on Dean’s mask was produced by John Lyndall in 1871. Lyndall’s mask, also created for firefighters, included a respirator to help to breathe. This combined respirator/filter became the precursor to masks used by firefighters to this day.4

Around World War II, HEPA (standing for high-efficiency particulate air) filters were introduced. The first models of these filters were large, bulky, expensive and utilized primarily in industrial applications. These early filters were developed by the military to purify air from atomic particles resulting from nuclear explosions. Although only mildly successful in this area, they did trap microscopic particles such as mold, pollen, bacteria and other airborne contaminants.5

In 1963, the United States passed the Clean Air Act, which set standards for national air quality. This legislation sparked advancements in air purification systems because it formally recognized the dangers of contaminants such as pesticides, building materials components and other commonly found airborne pollutants.

Filtering systems such as HEPA were improved and made practical for home use as well as more commercially viable on a wide commercial scale. Many companies, including Incen AG, IQAir North America, Austin Air Systems, AllerAir, and Blueair and others gradually entered the market, producing filtration systems not only for industrial use but also for the household and even for automobiles. Features, such as pre-filters to extend HEPA filter life and advanced air intake systems to improve efficiency were added to upgraded air purification models.6

Today’s air purification systems utilize a multitude of technologies for different filtering tasks. These systems can filter many contaminants and are widely used for industrial, hospital and home applications. Employing advanced technology, the units have become more efficient while being less expensive and more compact. The best filtering systems may use more than one technology, and we will examine these technologies below.

Air Purification Technologies

To maximize performance, today’s air purification systems use multiple filtering technologies, but most use HEPA filtration for ideal efficiency. With the use of HEPA technology, symptoms of particle pollution, such as allergies and asthma are reduced.

HEPA Air Purifiers

hepa FILTERThe tried and true purification system, HEPA was developed in the 1940s and is still the most popular and reliable filtration systems. HEPA, as defined by the Department of Energy, considered more of a standard than a particular technology, must trap 99.97% of particles larger than .3 microns in size and be capable of filtering 85 liters per minute.7 These filtering systems are typically based on either a paper or wire mesh system and form the underlying technology for many filtration systems.

These filters can be used alone or in combination with other technologies, such as electrostatic or activated charcoal systems for a complete purification. They are, however, incapable of filtering some contaminants such as those that are gas, rather than particulate based. Additionally, many filters that appear to be HEPA based, such as furnace filters, where looking to filter air efficiently, do not meet HEPA standards.8

In general, filters conforming to HEPA standards do a good job removing particulates from the air, but cannot cope with every filtration need. They cannot remove some contaminate types, and filters do require regular replacement.

Electrostatic Air Purifiers

Electrostatic air filters work by passing contaminated air through several layers of electrically charged wire mesh. As polluted air passes through the first layer, pollutant particles become positively charged by the friction between the filter and the air. As the now charged particles pass along through several layers of negatively charged mesh, their electrical charge attaches them to the filter wire. This adheres the particles in the filter matrix, trapping them and removing them from the airflow stream.

In theory, electrostatic filters never need to be replaced, only washed out, dried and replaced in their housing to continue their work. This can result in significant long-term cost savings over paper or wire mesh based filters. Cost savings can be up to $60 per year in a typical furnace filter application.

Electrostatic filters do have some drawbacks. Because they rely on static electricity to filter particles, they are good at filtering out small particles but have trouble with larger particles, such as dust or mold spores whose mass can overcome the attraction of the electrical charge. These larger contaminate particles are free to pass through the filter.

These filters do not require replacement but need frequent cleaning. If left uncleaned, they can build up contaminates that allow for other pollutants to pass through. Additionally, dirty filters can provide an organic matrix that can act as a breeding ground for mold, bacteria and other harmful agents. These pollutants can then break free from the filter and enter the environment. A dirty electrostatic filter can pollute more than no filter at all.

Cleaning a dirty filter can be a tedious task. Electrostatic filters can contain up to ten mesh layers, and the filter unit needs to be dismantled and each layer cleaned individually. This can be a time-consuming and dirty job.

Electrostatic filters also restrict airflow more than other filter types, in fact up to 50% of overall flow. This can place a strain on mechanical components, such as air conditioners or furnaces, resulting in loss of efficiency, increased energy costs and more frequent maintenance requirements.

Because only about 30% of particles are trapped, these contaminants are free to re-enter the environment and can be difficult to clean because they have become electronically charged and will want to stick to any surface on which they lodge.9

Ozone Generators

Ozone generators are intended to purify the air by producing ozone (O3). Sometimes called “activated oxygen,” ozone is one of the world’s most powerful sterilizers and can destroy bacteria, viruses, and other airborne pollutants.

Ozone can be generated by one of two methods. First, “corona discharge,” high voltage electricity is applied to a metallic grid which is held between to dielectric. As electricity jumps across the system, it breaks regular oxygen molecules (O2), and oxygen atoms bind with the remaining O2 molecules to form ozone.

Second, ultra-violet light can be passed can be passed through the air at a specific wavelength (254 nanometers), which causes O2 molecules to break down into single atoms. These atoms then bond with remaining O2 molecules to form ozone.

Produced ozone molecules are very short-lived and usually convert back to O2 molecules in about thirty minutes. But while ozone molecules are active, they can destroy contaminates by oxidizing these pollutants, killing bacteria or mold spores.10

On the surface, ozone generation appears an attractive alternative for air filtration. Ozone molecules are generated, do their job, then quickly dissipate. But it is not that simple. Several studies have indicated that to be effective, ozone, a very unstable and potentially dangerous gas would need to be generated at such high levels to be an effective air cleaner that these levels may be hazardous to humans. The high levels of ozone needed to do the job can result in breathing difficulties, respiratory infections and other health hazards.

Free ozone in the atmosphere can also combine with other chemical agents in the environment, such as gasses emitted from paint, carpets, etc. to form a dangerous chemical cocktail within the home. It is also difficult to determine the level of ozone produced by the generator or the level of other harmful chemicals emitted in the household environment and how the relative levels of these two agents will react with each other.

With the difficulties encountered with ozone generators, they are considered not suitable for home environments and should be used in industrial settings only.11

Ultraviolet Light Purifiers

Ultraviolet air purifiers work by exposing pathogens, such mold, bacteria and viruses to ultraviolet light. When exposed, the RNA and DNA in these pollutants breaks down, not specifically killing the pathogens, but rendering them relatively harmless to health. The effectiveness of the ultraviolet system depends on two factors: the strength of the ultraviolet light and how long pathogens are exposed to this light. The light, to be effective, must be presented very close to the offending agents.

Ultraviolet filters are not effective at and are not intended for, the removal of particulate matter from the air. These filters act only on organic agents, partially neutralizing their RND and DNS for a safer environment. For this reason, ultraviolet filters are typically used in combination with a HEPA system. The HEPA filter captures most contaminates, allowing the ultraviolet light to act more efficiently on the remaining viruses and bacteria. 12

Caution should be used when using an ultraviolet system, as continued exposure to the light contained in the filter unit can be dangerous. Additionally, the bulbs in ultraviolet systems may become less effective over time and require replacement for maximum efficiency. Some reports indicate that these bulbs loose about fifteen percent of their efficiency each year, making expensive replacements necessary. On the plus side, there is no filter to replace in an ultraviolet system (except in a system combined with a HEPA filter).13

Ultraviolet systems are not the answer for all air quality situations, but when used in combination with HEPA or other filtration systems, can provide the added benefit of rendering organic compounds harmless.

Activated Carbon Purifiers

When treated with oxygen, many holes open on the surface of the carbon. These pores can produce as much as 150 acres of surface area on a single pound of carbon, allowing the surface to trap and hold pollutants. Activated carbon filters can remove a long list of chemical agents from the air, including dangerous chemicals such as alcohols, organic acids, aldehydes, chlorinated hydrocarbons, ethers, esters, ketones, halogens, sulfur dioxide, sulfuric acid, and phosgene, resulting in an odor-free and cleaner environment.

Carbon filters work by the process of absorption, where airborne contaminants pass through the carbon pores and are chemically bonded to the carbon’s surface. Cleaned air then passes through the rest of the carbon, resulting in air that is free from pollutants.

Other elements such as zeolite, or potassium permanganate can be added to carbon to increase the filter’s efficiency. These elements help trap and neutralize smoke, organic vapors, and other contaminants such as off-gassing from plastics or paints, not caught by carbon alone.

Carbon filter elements do become saturated over time, depending on the pollutant load in the environment. The most effective filters contain many pounds of carbon for long life and maximum filtering efficiency. Carbon filters can quickly become clogged with dust and other environmental particulates. More carbon can, however, reduce air flow. For this reason, they are typically used in combination with a paper or wire-based HEPA filter element for a complete purification system.14


Ionizers work by passing polluted air over an electrically charged wire, or wire mesh a stream of producing charged molecules that enter the air. These molecules then interact with pollutants, binding with them and making them stick to surfaces, such as walls or floors, removing contaminates from the air. Some ionizers contain an oppositely charged plate that attracts the ionized pollutants, trapping them to be later cleaned from the system.

Differing types of these units either include or omit a fan to circulate the ionized air. Models with a fan circulate room air more rapidly but can be noisy and consume more energy. Fanless models circulate air more slowly, resulting in slower air purification, but are noiseless and energy efficient.15

Ionizers are attractive because they are silent (the fanless models) and have no moving parts. They require little maintenance and are compact for the home environment.

Some testing institutions, including Consumer Reports, have cautioned against the use of ionizers because they can produce ozone above a safe level of 50 parts per billion, in a sealed room test.16

Others, including Sharper Image, which filed and lost a lawsuit over the issue, dispute the Consumer Reports findings and contends that ionizers are safe for indoor use. Some testing laboratories have found that ionizers do very little to remove airborne contaminants and, considering the issues with ozone generation, do not recommend them ionizers for home use.17

Probiotic Air Purifiers

It may seem counterintuitive to introduce bacteria into the air to improve air quality, but that’s just what probiotic air purifiers do. This type of air purifier periodically releases beneficial bacteria into the environment which are intended to seek out and destroy harmful pathogens, including bacteria, mold, dander and other dangerous pollutants.

Typically installed in a furnace or air conditioning duct work, these units are silent, require little space and are low maintenance. The biotic canister on most models needs to be replaced approximately every six months. Other models include countertop units or even atomizing spray bottles that contain the beneficial bacteria.18

Where probiotic systems have been proven to be useful in tracking down and eliminating some organic pollutants, they are not effective against some types of pollution, including smoke, dust, VOCs and other household nuisances. For this reason, probiotic filtering systems should be used in conjunction with a HEPA system.


Many air purifiers, including those based on HEPA, electrostatic or activated carbon technologies, can quickly become clogged with large particles, typically dust or dander. For this reason, many air filtration units also contain a pre-filter. This filter traps large contaminate particles before they reach the costlier main filter, extending its life and effectiveness.


Any environment can be made safer and more pleasurable with the use of an air filtration system. The many types and sizes of these filters allow the home or office user to choose the right unit for their needs.

Units employing differing technologies, including HEPA, electrostatic, ozone generation, ultraviolet, activated carbon, ionization or probiotic technologies, each have their advantages and limitations. Some, such as HEPA and activated carbon, do a better job removing scores of particles from the atmosphere, while others such as probiotic or ozone generators are less efficient with significant pollutant particles but more efficient with organic agents.

Air filtration systems are not limited to employing only one technology. Many combine HEPA filters with pre-filters or other technologies, such as activated carbon to both enhance performance and improve longevity. A system based on multiple technologies may be right for many applications

Most filtration systems do require some form of maintenance. This can range from periodic cleaning to filter replacement. This adds to the cost and inconvenience of operating an air filtration system, but these drawbacks are outweighed by the benefits of having clean, breathable air in the office or work environment.

Using an air filtration system in the home or office can help those suffering from allergies, those with respiratory issues and those that just desire high quality of life by contributing to keep the air clean for a healthy environment.

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9 “Do Electrostatic Air Filters Work? The Pros and Cons of Washable Furnace Filters.”, All Systems Mechanical HVAC, Inc., accessed February 19, 2017,

10 “Questions and Answers About Ozone,” Ozone Solutions, accessed February 19, 2017,

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12 Allergy Consumer Review

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14 “Benefits of Activated Carbon Filters in Air Purifiers,” Clean Air Plus, accessed February 19, 2017,

15 Beach, Emily, “How Do Ionizers Work?”, the Livestrong Foundation, accessed February 19, 2017,

16 Consumer Reports, Consumer Reports Investigates Ionizing Air Cleaners: Five Models Are Not Recommended; Some Can Create Significant Levels Of Potentially Harmful Indoor Ozone”, accessed February 19, 2017,

17 “Ionizing Air Cleaners May Pose Health Hazard,” WebMD, accessed February 19, 2017,

18 “Better Air Cleans Sick Buildings With Probiotics,” Green Prophet, accessed February 19, 2017,

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