How Portable Air Purifiers Work

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How Portable Air Purifiers Remove Particle Pollutants

There are three ways that particulate pollutants are removed from indoor air by portable air purifiers. These include mechanical filtration, electronic precipitation and ion generation.

Most air purifiers also fall into similar classes based on the way they clean the air, i.e. mechanical filtration air purifiers, electronic precipitators and ion generators although new, hybrid air purifiers often combine two or more of these air purification technologies. There are also some variations of existing technologies such as those that offer air purification through "air washing" in water.

Particle Removal by Mechanical Filtration

Air purifiers utilizing mechanical filtration to remove particles from indoor air have two important elements, a fan and a filter or series of filters. The fan draws room air into the unit, passes it through the filter(s), and then expels filtered air back into the room. As the air goes through the filter(s), the process of mechanical filtration removes particulate from indoor air by capturing it on the filter media (the material the filter is made of).

Filters used to capture very small particles are generally designed to create as much surface area as possible. This is why such filters are typically pleated in order to maximize surface area.

Because they have a much greater surface area than a flat filter (such as a typical furnace filter) the filter can use much smaller fibers and pack them much more densely. This allows the filter to offer excellent levels of filtration of even very small particles without significantly increased resistance.

Mechanical filtration specifications are based on the percentage of particles  (filtration efficiency) of a specific size that a filter retains. Because the most harmful particles are quite small in size, it is important to select an air purifier that is capable of removing these particles in meaningful amounts in the environment where it will be used.

HEPA filtration is an excellent specification for an air purifier utilizing mechanical filtration and indicates that the unit captures 99.97% of particles as small as 0.3 micrometers.

Unfortunately, there is much misleading information disseminated by companies selling their products that confuses this issue. Thankfully, there is now an excellent standard known as Clean Air Delivery Rate (CADR) that can help consumers choose a high performance air purifier. Click here to learn more about CADR here.

You can also click here to find additional information necessary to understand filtration specifications, and here for information about choosing the right air purifier.

Particle Removal by "Air Washing"

There are also several companies on the market that offer appliances that both humidify and purify the air. These units all use water as the primary medium in which particulates are captured.

Some units of this type offer filtration of only relatively large particles as small as 10 micrometers in size while others utilize a variety of technologies such as ionization and the addition of mechanical filters to achieve extremely high levels of filtration, including HEPA filtration.

Particle Removal by Electrostatic Precipitation

Another way to remove particles from room air is by use of an electrical field to charge particles in incoming air, which, through a process known as electrostatic precipitation, are then deposited on collector plates.

This technology is highly effective and is used to control particulate pollution in many industrial processes. Air purifiers that use this technology are often referred to as electronic air cleaners or electrostatic precipitators.

Portable electrostatic precipitators utilize a fan to draw room air through an electrical field created by a high-voltage electrode or wire, which charges incoming airborne particles.

These charged particles are then passed through a series of oppositely charged collector plates where the particles are deposited on the collector plates in a process known as electrostatic precipitation.

Electrostatic precipitators do an excellent job removing particle pollution. Their efficiency will depend upon how much air flows through the unit, the size of the collection plates, how often the collector plates are cleaned (they become less efficient once contaminants build up beyond a certain level) and the strength of the electrical field.

Because there is so little resistance in an electronic air cleaner, energy costs are low to move air through the unit. Other advantages are that airflow remains constant and pollutants are removed simply by washing the collector plates by hand or in a dishwasher, thereby eliminating replacement filter costs. However, these plates must be cleaned frequently in order to remain efficient.

The major drawback to electrostatic precipitators is that most such units produce ozone. There is much confusion about ozone. We know that it's good in the upper atmosphere to protect us from the sun's UV radiation. We know it's bad at ground level as smog.

The U.S. EPA and OSHA have clearly indicated that even small amounts of ozone over extended periods of time may be harmful to human health. Because the ozone molecule has a third oxygen atom, (ozone is O3 while the oxygen we breathe is O2), this third atom is highly reactive and wants to bond with other substances such as dust, pollen and other indoor air pollution. But, the problem is that it will also bond with lung tissue and can prevent the follicles that help your lungs filter pollutants from functioning. This can result in serious respiratory illnesses and can really be a problem for asthma sufferers.

Many manufacturers of electrostatic precipitators claim that their units produce only very small amounts of ozone, below harmful levels as indicated by U.S. EPA. However, studies have repeatedly shown that many such units can build up dangerous levels of ozone in closed spaces over time. In the interests of health and safety it is impossible to recommend any air purifier that emits ozone.

Particle Removal by Negative Ion Generation

Negative ion generators sold as air purifiers charge the particles in room air. This causes them to be attracted to walls, floors, furnishings, window treatments, other contents and even people. Essentially, they remove the particles from the air and deposit them on everything else, creating significant soiling issues.

There are some negative ion generators that charge the air in a room and then draw the charged air back into the unit where the particles are then collected on an electrostatically charged filter in order to reduce room soiling.

Negative ion generators were originally developed in order to return a healthful balance of ions to indoor environments. There is an abundance of research that makes interesting claims concerning the health benefits of indoor air with a balanced amount of negative and positive ions. There is much controversy surrounding such research but many people do report improved health and/or well being when using such equipment.

However, most negative ion generators emit ozone as a by-product of the ion generation process. This is because, in order to function as an air purifier, large amounts of negative ions are needed. In order to accomplish this, an intense electrical field is required, and ozone is also generated along with large amounts of negative ions.

There are also air purifiers on the market that utilize what they call "Plasmacluster" technology to generate both positive and negative ions. These unstable ions are dispersed into room air and are said to be immediately surrounded by water molecules to form clusters that spread throughout the room. These then surround impurities such as odor molecules and are said to pierce the odor molecule to extract either hydrogen or nitrogen, thus inactivating the contaminant.

In addition, these Plasmaclusters attach to airborne particles, which makes them heavier than air, causing them to fall out onto floors and other surfaces.

There are also claims that this technology reduces airborne mold fungus by 90% but test results have not been provided. Whether or not this new technology produces ozone as a by-product is not known, though air purifiers that use negative ion generation for air purification typically do.

Particle Removal by Ozone Generation

Despite the fact that the U.S. EPA, OSHA and the American Lung Association have very clearly described the hazards of ozone generators being used for air purification, there are still an astounding number of companies marketing ozone generators for this purpose.

In spite of much marketing to the contrary, U.S. EPA states that, "Ozone does not remove particles (e.g., dust and pollen) from the air, including the particles that cause most allergies."

Based on the scientific evidence presented by highly credible organizations it is clear that ozone generators are ineffective and can be dangerous when used as indoor air purifiers. And, air purifiers that emit ozone as a by-product are also unsuitable and potentially harmful.

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